xunit3

ARCHITECTURE.md

@@ -355,11 +355,11 @@ Same caveat about duplicate entries applies.
 ### 5.9 GIF Export
 
 1. For each document in container, composite into RGBA buffer.
-2. Use external library (e.g. `SixLabors.ImageSharp`) to encode frames
-   with per-frame delay from `FrameDelayMs`.
-3. Output as animated GIF.
+2. Quantize each frame to 256 colors (popularity-based, with transparent slot).
+3. LZW-compress and write as GIF89a with per-frame delay from `FrameDelayMs`.
+4. NETSCAPE2.0 application extension for infinite looping.
 
-Only the GIF encoder is external; the `.minint` format is fully self-implemented.
+Fully self-implemented — no external library for GIF encoding.
 
 ### 5.10 Pattern Generation (Б4)
 
@@ -438,11 +438,11 @@ Canvas (`PixelCanvas` custom control):
 **Chosen**: eraser writes index 0 (transparent).
 **Rationale**: consistent with palette convention; compositing naturally handles it.
 
-### D7. GIF export library
+### D7. GIF export
 
-**Chosen**: external library for GIF encoding only (`SixLabors.ImageSharp` or equivalent).
-**Rationale**: GIF LZW compression is complex and not the focus of this project.
-**Constraint**: `.minint` serialization remains fully self-implemented.
+**Chosen**: fully self-implemented GIF89a encoder with LZW compression.
+**Rationale**: avoids external dependencies; the entire project uses only Avalonia and CommunityToolkit.Mvvm.
+**Details**: popularity-based color quantization to 256 colors, NETSCAPE2.0 looping extension.
 
 ### D8. No undo/redo in initial implementation
 
@@ -456,16 +456,16 @@ Canvas (`PixelCanvas` custom control):
 | Stage | Scope                                              |
 |-------|----------------------------------------------------|
 | 1     | ✅ Architecture & design (this document)            |
-| 2     | Solution scaffold + domain models                  |
-| 3     | Binary `.minint` serialization + round-trip test    |
-| 4     | Compositing + palette management + RGBA buffer      |
-| 5     | Basic Avalonia UI (main window, menus, panels)      |
-| 6     | Canvas: pan, zoom, grid, nearest-neighbor           |
-| 7     | Drawing tools: brush, eraser, flood fill, preview   |
-| 8     | Layer & document management UI                      |
-| 9     | Effects: contrast, grayscale, fragment copy, patterns |
-| 10    | Animation playback + BMP/GIF export                 |
-| 11    | Polish, tests, documentation                        |
+| 2     | ✅ Solution scaffold + domain models                |
+| 3     | ✅ Binary `.minint` serialization + round-trip test  |
+| 4     | ✅ Compositing + palette management + RGBA buffer    |
+| 5     | ✅ Basic Avalonia UI (main window, menus, panels)    |
+| 6     | ✅ Canvas: pan, zoom, grid, nearest-neighbor         |
+| 7     | ✅ Drawing tools: brush, eraser, flood fill, preview |
+| 8     | ✅ Layer & document management UI                    |
+| 9     | ✅ Effects: contrast, grayscale, fragment copy, patterns |
+| 10    | ✅ Animation playback + BMP/GIF export               |
+| 11    | ✅ Polish, tests, documentation                      |
 
 ---
 
@@ -477,6 +477,6 @@ Canvas (`PixelCanvas` custom control):
 | Avalonia.Desktop 11.3.8         | Minint (UI)    | Desktop host          |
 | Avalonia.Themes.Fluent 11.3.8   | Minint (UI)    | Theme                 |
 | CommunityToolkit.Mvvm 8.2.1    | Minint (UI)    | MVVM helpers          |
-| SixLabors.ImageSharp (TBD)     | Infrastructure | GIF export only       |
+| _(no external deps)_           | Infrastructure | GIF/BMP fully self-implemented |
 
 Core project: **zero** external dependencies.

FORMAT.md

@@ -0,0 +1,122 @@
+# Спецификация формата `.minint` (версия 1)
+
+## Общие сведения
+
+- Все многобайтовые целые числа — **little-endian**.
+- Строки — **UTF-8**, с префиксом длины 1 байт (макс. 255 байт).
+- Формат не использует сжатие — данные хранятся как есть.
+
+## Структура файла
+
+```
+┌──────────────────────────┐
+│   Container Header       │  28 байт (фиксированный)
+├──────────────────────────┤
+│   Document 1             │  (блок переменной длины)
+├──────────────────────────┤
+│   Document 2             │
+├──────────────────────────┤
+│   ...                    │
+├──────────────────────────┤
+│   Document N             │
+└──────────────────────────┘
+```
+
+## Container Header (28 байт)
+
+| Смещение | Размер | Тип    | Описание                        |
+|----------|--------|--------|---------------------------------|
+| 0        | 6      | ASCII  | Сигнатура: `MININT`             |
+| 6        | 2      | uint16 | Версия формата (текущая: `1`)   |
+| 8        | 4      | uint32 | Ширина (Width)                  |
+| 12       | 4      | uint32 | Высота (Height)                 |
+| 16       | 4      | uint32 | Количество документов           |
+| 20       | 8      | —      | Зарезервировано (нули)          |
+
+## Блок документа
+
+Повторяется `DocumentCount` раз, последовательно.
+
+### Заголовок документа
+
+| Размер              | Тип    | Описание                    |
+|---------------------|--------|-----------------------------|
+| 1                   | uint8  | Длина имени (NameLen)       |
+| NameLen             | UTF-8  | Имя документа               |
+| 4                   | uint32 | FrameDelayMs                |
+| 4                   | uint32 | Количество цветов (PalCnt)  |
+
+### Палитра
+
+`PalCnt × 4` байт. Каждый цвет: `[R, G, B, A]` (по 1 байту).
+
+Индекс 0 всегда соответствует прозрачному цвету `(0, 0, 0, 0)`.
+
+### Ширина индекса
+
+Вычисляется из `PalCnt` (не хранится в файле явно):
+
+| PalCnt              | Байт на индекс |
+|---------------------|-----------------|
+| 1 – 255             | 1               |
+| 256 – 65 535        | 2               |
+| 65 536 – 16 777 215 | 3              |
+| 16 777 216+         | 4               |
+
+### Количество слоёв
+
+| Размер | Тип    | Описание          |
+|--------|--------|-------------------|
+| 4      | uint32 | Количество слоёв  |
+
+### Блок слоя
+
+Повторяется `LayerCount` раз.
+
+| Размер                    | Тип   | Описание                           |
+|---------------------------|-------|------------------------------------|
+| 1                         | uint8 | Длина имени слоя (LayerNameLen)    |
+| LayerNameLen              | UTF-8 | Имя слоя                          |
+| 1                         | uint8 | Видимость (0 = скрыт, 1 = виден)  |
+| 1                         | uint8 | Opacity (0–255)                    |
+| Width × Height × ByteWidth | bytes | Индексы палитры, row-major, LE    |
+
+## Правила валидации
+
+1. Сигнатура — строго `MININT` (6 байт ASCII).
+2. Версия — строго `1` (неизвестные версии отклоняются).
+3. Width, Height >= 1; максимум 65 536.
+4. DocumentCount >= 1.
+5. PaletteCount >= 1.
+6. Каждый индекс пикселя < PaletteCount.
+7. IsVisible — только 0 или 1.
+8. Зарезервированные байты — допускаются ненулевые (forward compatibility).
+9. Неожиданный конец файла — ошибка с описанием контекста.
+
+## Пример
+
+Контейнер 4×4, 1 документ, 2 цвета (прозрачный + красный), 1 слой:
+
+```
+4D 49 4E 49 4E 54          — "MININT"
+01 00                       — version 1
+04 00 00 00                 — width = 4
+04 00 00 00                 — height = 4
+01 00 00 00                 — 1 document
+00 00 00 00 00 00 00 00     — reserved
+
+05                          — name length = 5
+44 6F 63 20 31              — "Doc 1"
+64 00 00 00                 — FrameDelayMs = 100
+02 00 00 00                 — palette count = 2
+00 00 00 00                 — color 0: transparent
+FF 00 00 FF                 — color 1: red (R=255, G=0, B=0, A=255)
+
+01 00 00 00                 — 1 layer
+07                          — layer name length = 7
+4C 61 79 65 72 20 31        — "Layer 1"
+01                          — visible
+FF                          — opacity = 255
+00 00 00 00 00 00 00 00     — 16 pixels, all index 0 (transparent)
+00 00 00 00 00 00 00 00
+```

Minint.Infrastructure/Export/BmpExporter.cs

@@ -0,0 +1,80 @@
+using Minint.Core.Services;
+
+namespace Minint.Infrastructure.Export;
+
+/// <summary>
+/// Writes a 32-bit BGRA BMP (BITMAPV4HEADER) from an ARGB pixel buffer.
+/// BMP rows are bottom-up, so we flip vertically during write.
+/// </summary>
+public sealed class BmpExporter : IBmpExporter
+{
+    private const int BmpFileHeaderSize = 14;
+    private const int BitmapV4HeaderSize = 108;
+    private const int HeadersTotal = BmpFileHeaderSize + BitmapV4HeaderSize;
+
+    public void Export(Stream stream, uint[] pixels, int width, int height)
+    {
+        ArgumentNullException.ThrowIfNull(stream);
+        ArgumentNullException.ThrowIfNull(pixels);
+        if (pixels.Length != width * height)
+            throw new ArgumentException("Pixel buffer size does not match dimensions.");
+
+        int rowBytes = width * 4;
+        int imageSize = rowBytes * height;
+        int fileSize = HeadersTotal + imageSize;
+
+        using var w = new BinaryWriter(stream, System.Text.Encoding.UTF8, leaveOpen: true);
+
+        // BITMAPFILEHEADER (14 bytes)
+        w.Write((byte)'B');
+        w.Write((byte)'M');
+        w.Write(fileSize);
+        w.Write((ushort)0); // reserved1
+        w.Write((ushort)0); // reserved2
+        w.Write(HeadersTotal); // pixel data offset
+
+        // BITMAPV4HEADER (108 bytes)
+        w.Write(BitmapV4HeaderSize);
+        w.Write(width);
+        w.Write(height); // positive = bottom-up
+        w.Write((ushort)1); // planes
+        w.Write((ushort)32); // bpp
+        w.Write(3); // biCompression = BI_BITFIELDS
+        w.Write(imageSize);
+        w.Write(2835); // X pixels per meter (~72 DPI)
+        w.Write(2835); // Y pixels per meter
+        w.Write(0); // colors used
+        w.Write(0); // important colors
+
+        // Channel masks (BGRA order in file)
+        w.Write(0x00FF0000u); // red mask
+        w.Write(0x0000FF00u); // green mask
+        w.Write(0x000000FFu); // blue mask
+        w.Write(0xFF000000u); // alpha mask
+
+        // Color space type: LCS_sRGB
+        w.Write(0x73524742); // 'sRGB'
+        // CIEXYZTRIPLE endpoints (36 bytes zeroed)
+        w.Write(new byte[36]);
+        // Gamma RGB (12 bytes zeroed)
+        w.Write(new byte[12]);
+
+        // Pixel data: BMP is bottom-up, our buffer is top-down
+        for (int y = height - 1; y >= 0; y--)
+        {
+            int rowStart = y * width;
+            for (int x = 0; x < width; x++)
+            {
+                uint argb = pixels[rowStart + x];
+                byte a = (byte)(argb >> 24);
+                byte r = (byte)((argb >> 16) & 0xFF);
+                byte g = (byte)((argb >> 8) & 0xFF);
+                byte b = (byte)(argb & 0xFF);
+                w.Write(b);
+                w.Write(g);
+                w.Write(r);
+                w.Write(a);
+            }
+        }
+    }
+}

Minint.Infrastructure/Export/GifExporter.cs

@@ -0,0 +1,329 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using Minint.Core.Services;
+
+namespace Minint.Infrastructure.Export;
+
+/// <summary>
+/// Self-implemented GIF89a animated exporter.
+/// Quantizes each ARGB frame to 256 colors (including transparent) using popularity.
+/// Uses LZW compression as required by the GIF spec.
+/// </summary>
+public sealed class GifExporter : IGifExporter
+{
+    public void Export(Stream stream, IReadOnlyList<(uint[] Pixels, uint DelayMs)> frames, int width, int height)
+    {
+        ArgumentNullException.ThrowIfNull(stream);
+        if (frames.Count == 0)
+            throw new ArgumentException("At least one frame is required.");
+
+        using var w = new BinaryWriter(stream, System.Text.Encoding.UTF8, leaveOpen: true);
+
+        WriteGifHeader(w, width, height);
+        WriteNetscapeExtension(w); // infinite loop
+
+        foreach (var (pixels, delayMs) in frames)
+        {
+            var (palette, indices, transparentIndex) = Quantize(pixels, width * height);
+            int colorBits = GetColorBits(palette.Length);
+            int tableSize = 1 << colorBits;
+
+            WriteGraphicControlExtension(w, delayMs, transparentIndex);
+            WriteImageDescriptor(w, width, height, colorBits);
+            WriteColorTable(w, palette, tableSize);
+            WriteLzwImageData(w, indices, colorBits);
+        }
+
+        w.Write((byte)0x3B); // GIF trailer
+    }
+
+    private static void WriteGifHeader(BinaryWriter w, int width, int height)
+    {
+        w.Write("GIF89a"u8.ToArray());
+        w.Write((ushort)width);
+        w.Write((ushort)height);
+        // Global color table flag=0, color resolution=7, sort=0, gct size=0
+        w.Write((byte)0x70);
+        w.Write((byte)0); // background color index
+        w.Write((byte)0); // pixel aspect ratio
+    }
+
+    private static void WriteNetscapeExtension(BinaryWriter w)
+    {
+        w.Write((byte)0x21); // extension introducer
+        w.Write((byte)0xFF); // application extension
+        w.Write((byte)11); // block size
+        w.Write("NETSCAPE2.0"u8.ToArray());
+        w.Write((byte)3); // sub-block size
+        w.Write((byte)1); // sub-block ID
+        w.Write((ushort)0); // loop count: 0 = infinite
+        w.Write((byte)0); // block terminator
+    }
+
+    private static void WriteGraphicControlExtension(BinaryWriter w, uint delayMs, int transparentIndex)
+    {
+        w.Write((byte)0x21); // extension introducer
+        w.Write((byte)0xF9); // graphic control label
+        w.Write((byte)4); // block size
+        byte packed = (byte)(transparentIndex >= 0 ? 0x09 : 0x08);
+        // disposal method=2 (restore to background), no user input, transparent flag
+        w.Write(packed);
+        ushort delayCs = (ushort)(delayMs / 10); // GIF delay is in centiseconds
+        if (delayCs == 0 && delayMs > 0) delayCs = 1;
+        w.Write(delayCs);
+        w.Write((byte)(transparentIndex >= 0 ? transparentIndex : 0));
+        w.Write((byte)0); // block terminator
+    }
+
+    private static void WriteImageDescriptor(BinaryWriter w, int width, int height, int colorBits)
+    {
+        w.Write((byte)0x2C); // image separator
+        w.Write((ushort)0); // left
+        w.Write((ushort)0); // top
+        w.Write((ushort)width);
+        w.Write((ushort)height);
+        byte packed = (byte)(0x80 | (colorBits - 1)); // local color table, not interlaced
+        w.Write(packed);
+    }
+
+    private static void WriteColorTable(BinaryWriter w, byte[][] palette, int tableSize)
+    {
+        for (int i = 0; i < tableSize; i++)
+        {
+            if (i < palette.Length)
+            {
+                w.Write(palette[i][0]); // R
+                w.Write(palette[i][1]); // G
+                w.Write(palette[i][2]); // B
+            }
+            else
+            {
+                w.Write((byte)0);
+                w.Write((byte)0);
+                w.Write((byte)0);
+            }
+        }
+    }
+
+    #region LZW compression
+
+    private static void WriteLzwImageData(BinaryWriter w, byte[] indices, int colorBits)
+    {
+        int minCodeSize = Math.Max(colorBits, 2);
+        w.Write((byte)minCodeSize);
+
+        var output = new List<byte>();
+        LzwCompress(indices, minCodeSize, output);
+
+        int offset = 0;
+        while (offset < output.Count)
+        {
+            int blockLen = Math.Min(255, output.Count - offset);
+            w.Write((byte)blockLen);
+            for (int i = 0; i < blockLen; i++)
+                w.Write(output[offset + i]);
+            offset += blockLen;
+        }
+        w.Write((byte)0); // block terminator
+    }
+
+    private static void LzwCompress(byte[] indices, int minCodeSize, List<byte> output)
+    {
+        int clearCode = 1 << minCodeSize;
+        int eoiCode = clearCode + 1;
+
+        int codeSize = minCodeSize + 1;
+        int nextCode = eoiCode + 1;
+        int maxCode = (1 << codeSize) - 1;
+
+        var table = new Dictionary<(int Prefix, byte Suffix), int>();
+
+        int bitBuffer = 0;
+        int bitCount = 0;
+
+        void EmitCode(int code)
+        {
+            bitBuffer |= code << bitCount;
+            bitCount += codeSize;
+            while (bitCount >= 8)
+            {
+                output.Add((byte)(bitBuffer & 0xFF));
+                bitBuffer >>= 8;
+                bitCount -= 8;
+            }
+        }
+
+        void ResetTable()
+        {
+            table.Clear();
+            codeSize = minCodeSize + 1;
+            nextCode = eoiCode + 1;
+            maxCode = (1 << codeSize) - 1;
+        }
+
+        EmitCode(clearCode);
+        ResetTable();
+
+        if (indices.Length == 0)
+        {
+            EmitCode(eoiCode);
+            if (bitCount > 0) output.Add((byte)(bitBuffer & 0xFF));
+            return;
+        }
+
+        int prefix = indices[0];
+
+        for (int i = 1; i < indices.Length; i++)
+        {
+            byte suffix = indices[i];
+            var key = (prefix, suffix);
+
+            if (table.TryGetValue(key, out int existing))
+            {
+                prefix = existing;
+            }
+            else
+            {
+                EmitCode(prefix);
+
+                if (nextCode <= 4095)
+                {
+                    table[key] = nextCode++;
+                    if (nextCode > maxCode + 1 && codeSize < 12)
+                    {
+                        codeSize++;
+                        maxCode = (1 << codeSize) - 1;
+                    }
+                }
+                else
+                {
+                    EmitCode(clearCode);
+                    ResetTable();
+                }
+
+                prefix = suffix;
+            }
+        }
+
+        EmitCode(prefix);
+        EmitCode(eoiCode);
+        if (bitCount > 0) output.Add((byte)(bitBuffer & 0xFF));
+    }
+
+    #endregion
+
+    #region Quantization
+
+    /// <summary>
+    /// Quantizes ARGB pixels to max 256 palette entries.
+    /// Reserves index 0 for transparent if any pixel has alpha &lt; 128.
+    /// Uses popularity-based selection for opaque colors.
+    /// </summary>
+    private static (byte[][] Palette, byte[] Indices, int TransparentIndex) Quantize(uint[] argb, int count)
+    {
+        bool hasTransparency = false;
+        var colorCounts = new Dictionary<uint, int>();
+
+        for (int i = 0; i < count; i++)
+        {
+            uint px = argb[i];
+            byte a = (byte)(px >> 24);
+            if (a < 128)
+            {
+                hasTransparency = true;
+                continue;
+            }
+            uint opaque = px | 0xFF000000u;
+            colorCounts.TryGetValue(opaque, out int c);
+            colorCounts[opaque] = c + 1;
+        }
+
+        int transparentIndex = hasTransparency ? 0 : -1;
+        int maxColors = hasTransparency ? 255 : 256;
+
+        var sorted = new List<KeyValuePair<uint, int>>(colorCounts);
+        sorted.Sort((a, b) => b.Value.CompareTo(a.Value));
+        if (sorted.Count > maxColors)
+            sorted.RemoveRange(maxColors, sorted.Count - maxColors);
+
+        var palette = new List<byte[]>();
+        var colorToIndex = new Dictionary<uint, byte>();
+
+        if (hasTransparency)
+        {
+            palette.Add([0, 0, 0]); // transparent slot
+        }
+
+        foreach (var kv in sorted)
+        {
+            uint px = kv.Key;
+            byte idx = (byte)palette.Count;
+            palette.Add([
+                (byte)((px >> 16) & 0xFF),
+                (byte)((px >> 8) & 0xFF),
+                (byte)(px & 0xFF)
+            ]);
+            colorToIndex[px] = idx;
+        }
+
+        if (palette.Count == 0)
+            palette.Add([0, 0, 0]);
+
+        var indices = new byte[count];
+        for (int i = 0; i < count; i++)
+        {
+            uint px = argb[i];
+            byte a = (byte)(px >> 24);
+            if (a < 128)
+            {
+                indices[i] = (byte)(transparentIndex >= 0 ? transparentIndex : 0);
+                continue;
+            }
+
+            uint opaque = px | 0xFF000000u;
+            if (colorToIndex.TryGetValue(opaque, out byte idx))
+            {
+                indices[i] = idx;
+            }
+            else
+            {
+                indices[i] = FindClosest(opaque, palette, hasTransparency ? 1 : 0);
+            }
+        }
+
+        return (palette.ToArray(), indices, transparentIndex);
+    }
+
+    private static byte FindClosest(uint argb, List<byte[]> palette, int startIdx)
+    {
+        byte r = (byte)((argb >> 16) & 0xFF);
+        byte g = (byte)((argb >> 8) & 0xFF);
+        byte b = (byte)(argb & 0xFF);
+
+        int bestIdx = startIdx;
+        int bestDist = int.MaxValue;
+        for (int i = startIdx; i < palette.Count; i++)
+        {
+            int dr = r - palette[i][0];
+            int dg = g - palette[i][1];
+            int db = b - palette[i][2];
+            int dist = dr * dr + dg * dg + db * db;
+            if (dist < bestDist)
+            {
+                bestDist = dist;
+                bestIdx = i;
+            }
+        }
+        return (byte)bestIdx;
+    }
+
+    private static int GetColorBits(int paletteCount)
+    {
+        int bits = 2;
+        while ((1 << bits) < paletteCount) bits++;
+        return Math.Min(bits, 8);
+    }
+
+    #endregion
+}

Minint.Tests/CompositorTests.cs

@@ -0,0 +1,76 @@
+using Minint.Core.Models;
+using Minint.Core.Services.Impl;
+
+namespace Minint.Tests;
+
+public class CompositorTests
+{
+    private readonly Compositor _compositor = new();
+
+    [Fact]
+    public void Composite_EmptyLayer_AllTransparent()
+    {
+        var doc = new MinintDocument("test");
+        doc.Layers.Add(new MinintLayer("L1", 4));
+
+        uint[] result = _compositor.Composite(doc, 2, 2);
+
+        Assert.All(result, px => Assert.Equal(0u, px));
+    }
+
+    [Fact]
+    public void Composite_SingleOpaquePixel()
+    {
+        var doc = new MinintDocument("test");
+        var red = new RgbaColor(255, 0, 0, 255);
+        doc.EnsureColorCached(red);
+        var layer = new MinintLayer("L1", 4);
+        layer.Pixels[0] = 1;
+        doc.Layers.Add(layer);
+
+        uint[] result = _compositor.Composite(doc, 2, 2);
+
+        // ARGB packed as 0xAARRGGBB
+        uint expected = 0xFF_FF_00_00u;
+        Assert.Equal(expected, result[0]);
+        Assert.Equal(0u, result[1]); // rest is transparent
+    }
+
+    [Fact]
+    public void Composite_HiddenLayer_Ignored()
+    {
+        var doc = new MinintDocument("test");
+        doc.EnsureColorCached(new RgbaColor(0, 255, 0, 255));
+        var layer = new MinintLayer("L1", 4);
+        layer.Pixels[0] = 1;
+        layer.IsVisible = false;
+        doc.Layers.Add(layer);
+
+        uint[] result = _compositor.Composite(doc, 2, 2);
+
+        Assert.Equal(0u, result[0]);
+    }
+
+    [Fact]
+    public void Composite_TwoLayers_TopOverBottom()
+    {
+        var doc = new MinintDocument("test");
+        var red = new RgbaColor(255, 0, 0, 255);
+        var blue = new RgbaColor(0, 0, 255, 255);
+        int redIdx = doc.EnsureColorCached(red);
+        int blueIdx = doc.EnsureColorCached(blue);
+
+        var bottom = new MinintLayer("bottom", 1);
+        bottom.Pixels[0] = redIdx;
+        var top = new MinintLayer("top", 1);
+        top.Pixels[0] = blueIdx;
+
+        doc.Layers.Add(bottom);
+        doc.Layers.Add(top);
+
+        uint[] result = _compositor.Composite(doc, 1, 1);
+
+        // Blue on top, fully opaque, should overwrite red
+        Assert.Equal(0xFF_00_00_FFu, result[0]);
+    }
+}

Minint.Tests/DrawingTests.cs

@@ -0,0 +1,63 @@
+using Minint.Core.Models;
+using Minint.Core.Services.Impl;
+
+namespace Minint.Tests;
+
+public class DrawingTests
+{
+    private readonly DrawingService _drawing = new();
+
+    [Fact]
+    public void ApplyBrush_Radius0_SetsSinglePixel()
+    {
+        var layer = new MinintLayer("L1", 9);
+        _drawing.ApplyBrush(layer, 1, 1, 0, 1, 3, 3);
+
+        Assert.Equal(1, layer.Pixels[1 * 3 + 1]);
+        Assert.Equal(0, layer.Pixels[0]); // (0,0) untouched
+    }
+
+    [Fact]
+    public void ApplyBrush_Radius1_SetsCircle()
+    {
+        var layer = new MinintLayer("L1", 25);
+        _drawing.ApplyBrush(layer, 2, 2, 1, 1, 5, 5);
+
+        // Center + 4 neighbors should be set
+        Assert.Equal(1, layer.Pixels[2 * 5 + 2]); // center
+        Assert.Equal(1, layer.Pixels[1 * 5 + 2]); // top
+        Assert.Equal(1, layer.Pixels[3 * 5 + 2]); // bottom
+        Assert.Equal(1, layer.Pixels[2 * 5 + 1]); // left
+        Assert.Equal(1, layer.Pixels[2 * 5 + 3]); // right
+    }
+
+    [Fact]
+    public void ApplyEraser_SetsToZero()
+    {
+        var layer = new MinintLayer("L1", 9);
+        Array.Fill(layer.Pixels, 5);
+        _drawing.ApplyEraser(layer, 1, 1, 0, 3, 3);
+
+        Assert.Equal(0, layer.Pixels[1 * 3 + 1]);
+        Assert.Equal(5, layer.Pixels[0]); // untouched
+    }
+
+    [Fact]
+    public void GetBrushMask_Radius0_SinglePixel()
+    {
+        var mask = _drawing.GetBrushMask(2, 2, 0, 5, 5);
+        Assert.Single(mask);
+        Assert.Equal((2, 2), mask[0]);
+    }
+
+    [Fact]
+    public void GetBrushMask_OutOfBounds_Clamped()
+    {
+        var mask = _drawing.GetBrushMask(0, 0, 2, 3, 3);
+        Assert.All(mask, p =>
+        {
+            Assert.InRange(p.X, 0, 2);
+            Assert.InRange(p.Y, 0, 2);
+        });
+    }
+}

Minint.Tests/ExportTests.cs

@@ -0,0 +1,68 @@
+using System.Text;
+using Minint.Core.Models;
+using Minint.Core.Services.Impl;
+using Minint.Infrastructure.Export;
+
+namespace Minint.Tests;
+
+public class ExportTests
+{
+    [Fact]
+    public void BmpExport_WritesValidBmp()
+    {
+        var exporter = new BmpExporter();
+        var pixels = new uint[] { 0xFF_FF_00_00, 0xFF_00_FF_00, 0xFF_00_00_FF, 0xFF_FF_FF_FF };
+
+        var ms = new MemoryStream();
+        exporter.Export(ms, pixels, 2, 2);
+
+        ms.Position = 0;
+        byte[] data = ms.ToArray();
+
+        Assert.True(data.Length > 0);
+        Assert.Equal((byte)'B', data[0]);
+        Assert.Equal((byte)'M', data[1]);
+
+        int fileSize = BitConverter.ToInt32(data, 2);
+        Assert.Equal(data.Length, fileSize);
+    }
+
+    [Fact]
+    public void GifExport_WritesValidGif()
+    {
+        var exporter = new GifExporter();
+        var frame1 = new uint[16]; // 4x4 transparent
+        var frame2 = new uint[16];
+        Array.Fill(frame2, 0xFF_FF_00_00u);
+
+        var frames = new List<(uint[] Pixels, uint DelayMs)>
+        {
+            (frame1, 100),
+            (frame2, 200),
+        };
+
+        var ms = new MemoryStream();
+        exporter.Export(ms, frames, 4, 4);
+
+        ms.Position = 0;
+        byte[] data = ms.ToArray();
+
+        Assert.True(data.Length > 0);
+        string sig = Encoding.ASCII.GetString(data, 0, 6);
+        Assert.Equal("GIF89a", sig);
+        Assert.Equal(0x3B, data[^1]); // GIF trailer
+    }
+
+    [Fact]
+    public void BmpExport_DimensionMismatch_Throws()
+    {
+        var exporter = new BmpExporter();
+        var pixels = new uint[3]; // does not match 2x2
+
+        Assert.Throws<ArgumentException>(() =>
+        {
+            var ms = new MemoryStream();
+            exporter.Export(ms, pixels, 2, 2);
+        });
+    }
+}

Minint.Tests/FloodFillTests.cs

@@ -0,0 +1,52 @@
+using Minint.Core.Models;
+using Minint.Core.Services.Impl;
+
+namespace Minint.Tests;
+
+public class FloodFillTests
+{
+    private readonly FloodFillService _fill = new();
+
+    [Fact]
+    public void Fill_EmptyLayer_FillsAll()
+    {
+        var layer = new MinintLayer("L1", 9); // 3x3, all zeros
+        _fill.Fill(layer, 0, 0, 1, 3, 3);
+
+        Assert.All(layer.Pixels, px => Assert.Equal(1, px));
+    }
+
+    [Fact]
+    public void Fill_SameColor_NoOp()
+    {
+        var layer = new MinintLayer("L1", 4);
+        Array.Fill(layer.Pixels, 2);
+        _fill.Fill(layer, 0, 0, 2, 2, 2);
+
+        Assert.All(layer.Pixels, px => Assert.Equal(2, px));
+    }
+
+    [Fact]
+    public void Fill_Bounded_DoesNotCrossBorder()
+    {
+        // 3x3 grid with a wall:
+        // 0 0 0
+        // 1 1 1
+        // 0 0 0
+        var layer = new MinintLayer("L1", 9);
+        layer.Pixels[3] = 1; // (0,1)
+        layer.Pixels[4] = 1; // (1,1)
+        layer.Pixels[5] = 1; // (2,1)
+
+        _fill.Fill(layer, 0, 0, 2, 3, 3);
+
+        // Top row should be filled
+        Assert.Equal(2, layer.Pixels[0]);
+        Assert.Equal(2, layer.Pixels[1]);
+        Assert.Equal(2, layer.Pixels[2]);
+        // Wall untouched
+        Assert.Equal(1, layer.Pixels[3]);
+        // Bottom row untouched (blocked by wall)
+        Assert.Equal(0, layer.Pixels[6]);
+    }
+}

Minint.Tests/FragmentServiceTests.cs

@@ -0,0 +1,68 @@
+using Minint.Core.Models;
+using Minint.Core.Services.Impl;
+
+namespace Minint.Tests;
+
+public class FragmentServiceTests
+{
+    private readonly FragmentService _fragment = new();
+
+    [Fact]
+    public void CopyFragment_SameDocument_CopiesPixels()
+    {
+        var doc = new MinintDocument("test");
+        var red = new RgbaColor(255, 0, 0, 255);
+        doc.EnsureColorCached(red);
+
+        var src = new MinintLayer("src", 16);
+        src.Pixels[0] = 1; // (0,0) = red
+        src.Pixels[1] = 1; // (1,0) = red
+        doc.Layers.Add(src);
+
+        var dst = new MinintLayer("dst", 16);
+        doc.Layers.Add(dst);
+
+        _fragment.CopyFragment(doc, 0, 0, 0, 2, 1, doc, 1, 2, 2, 4, 4);
+
+        Assert.Equal(1, dst.Pixels[2 * 4 + 2]); // (2,2)
+        Assert.Equal(1, dst.Pixels[2 * 4 + 3]); // (3,2)
+    }
+
+    [Fact]
+    public void CopyFragment_DifferentDocuments_MergesPalette()
+    {
+        var srcDoc = new MinintDocument("src");
+        var blue = new RgbaColor(0, 0, 255, 255);
+        int blueIdx = srcDoc.EnsureColorCached(blue);
+        var srcLayer = new MinintLayer("L1", 4);
+        srcLayer.Pixels[0] = blueIdx;
+        srcDoc.Layers.Add(srcLayer);
+
+        var dstDoc = new MinintDocument("dst");
+        var dstLayer = new MinintLayer("L1", 4);
+        dstDoc.Layers.Add(dstLayer);
+
+        _fragment.CopyFragment(srcDoc, 0, 0, 0, 1, 1, dstDoc, 0, 0, 0, 2, 2);
+
+        int dstBlueIdx = dstDoc.FindColorCached(blue);
+        Assert.True(dstBlueIdx > 0);
+        Assert.Equal(dstBlueIdx, dstLayer.Pixels[0]);
+    }
+
+    [Fact]
+    public void CopyFragment_TransparentPixels_Skipped()
+    {
+        var doc = new MinintDocument("test");
+        var src = new MinintLayer("src", 4); // all zeros (transparent)
+        doc.Layers.Add(src);
+
+        var dst = new MinintLayer("dst", 4);
+        Array.Fill(dst.Pixels, 0);
+        dst.Pixels[0] = 0; // explicitly 0
+        doc.Layers.Add(dst);
+
+        _fragment.CopyFragment(doc, 0, 0, 0, 2, 2, doc, 1, 0, 0, 2, 2);
+
+        Assert.Equal(0, dst.Pixels[0]); // stays transparent
+    }
+}

Minint.Tests/ImageEffectsTests.cs

@@ -0,0 +1,65 @@
+using Minint.Core.Models;
+using Minint.Core.Services.Impl;
+
+namespace Minint.Tests;
+
+public class ImageEffectsTests
+{
+    private readonly ImageEffectsService _effects = new();
+
+    [Fact]
+    public void ApplyGrayscale_ConvertsColors()
+    {
+        var doc = new MinintDocument("test");
+        var red = new RgbaColor(255, 0, 0, 255);
+        doc.EnsureColorCached(red);
+
+        _effects.ApplyGrayscale(doc);
+
+        var gray = doc.Palette[1];
+        Assert.Equal(gray.R, gray.G);
+        Assert.Equal(gray.G, gray.B);
+        Assert.Equal(255, gray.A);
+        // BT.601: 0.299*255 ≈ 76
+        Assert.InRange(gray.R, 74, 78);
+    }
+
+    [Fact]
+    public void ApplyGrayscale_PreservesTransparentIndex()
+    {
+        var doc = new MinintDocument("test");
+        doc.EnsureColorCached(new RgbaColor(100, 200, 50, 255));
+
+        _effects.ApplyGrayscale(doc);
+
+        Assert.Equal(RgbaColor.Transparent, doc.Palette[0]);
+    }
+
+    [Fact]
+    public void ApplyContrast_IncreasesContrast()
+    {
+        var doc = new MinintDocument("test");
+        var midGray = new RgbaColor(128, 128, 128, 255);
+        var lightGray = new RgbaColor(192, 192, 192, 255);
+        doc.EnsureColorCached(midGray);
+        doc.EnsureColorCached(lightGray);
+
+        _effects.ApplyContrast(doc, 2.0);
+
+        // midGray (128) stays ~128: factor*(128-128)+128 = 128
+        Assert.InRange(doc.Palette[1].R, 126, 130);
+        // lightGray (192): factor*(192-128)+128 = 2*64+128 = 256 → clamped to 255
+        Assert.Equal(255, doc.Palette[2].R);
+    }
+
+    [Fact]
+    public void ApplyContrast_PreservesAlpha()
+    {
+        var doc = new MinintDocument("test");
+        doc.EnsureColorCached(new RgbaColor(100, 100, 100, 200));
+
+        _effects.ApplyContrast(doc, 1.5);
+
+        Assert.Equal(200, doc.Palette[1].A);
+    }
+}

Minint.Tests/Minint.Tests.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>
+    <UseMicrosoftTestingPlatformRunner>true</UseMicrosoftTestingPlatformRunner>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Minint.Core\Minint.Core.csproj" />
+    <ProjectReference Include="..\Minint.Infrastructure\Minint.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>

Minint.Tests/PatternGeneratorTests.cs

@@ -0,0 +1,41 @@
+using Minint.Core.Models;
+using Minint.Core.Services;
+using Minint.Core.Services.Impl;
+
+namespace Minint.Tests;
+
+public class PatternGeneratorTests
+{
+    private readonly PatternGenerator _gen = new();
+
+    [Theory]
+    [InlineData(PatternType.Checkerboard)]
+    [InlineData(PatternType.HorizontalGradient)]
+    [InlineData(PatternType.VerticalGradient)]
+    [InlineData(PatternType.HorizontalStripes)]
+    [InlineData(PatternType.VerticalStripes)]
+    [InlineData(PatternType.ConcentricCircles)]
+    [InlineData(PatternType.Tile)]
+    public void Generate_AllTypes_ProducesValidDocument(PatternType type)
+    {
+        var colors = new[] { new RgbaColor(255, 0, 0, 255), new RgbaColor(0, 0, 255, 255) };
+        var doc = _gen.Generate(type, 16, 16, colors, 4, 4);
+
+        Assert.Equal($"Pattern ({type})", doc.Name);
+        Assert.Single(doc.Layers);
+        Assert.Equal(256, doc.Layers[0].Pixels.Length);
+        Assert.True(doc.Palette.Count >= 2);
+    }
+
+    [Fact]
+    public void Generate_Checkerboard_AlternatesColors()
+    {
+        var colors = new[] { new RgbaColor(255, 0, 0, 255), new RgbaColor(0, 255, 0, 255) };
+        var doc = _gen.Generate(PatternType.Checkerboard, 4, 4, colors, 2);
+
+        var layer = doc.Layers[0];
+        int topLeft = layer.Pixels[0];
+        int topRight = layer.Pixels[2]; // cellSize=2, so (2,0) is next cell
+        Assert.NotEqual(topLeft, topRight);
+    }
+}

Minint.Tests/SerializerTests.cs

@@ -0,0 +1,121 @@
+using Minint.Core.Models;
+using Minint.Infrastructure.Serialization;
+
+namespace Minint.Tests;
+
+public class SerializerTests
+{
+    private readonly MinintSerializer _serializer = new();
+
+    [Fact]
+    public void RoundTrip_EmptyDocument_PreservesStructure()
+    {
+        var container = new MinintContainer(32, 16);
+        container.AddNewDocument("Doc1");
+
+        var result = RoundTrip(container);
+
+        Assert.Equal(32, result.Width);
+        Assert.Equal(16, result.Height);
+        Assert.Single(result.Documents);
+        Assert.Equal("Doc1", result.Documents[0].Name);
+        Assert.Single(result.Documents[0].Layers);
+        Assert.Equal(32 * 16, result.Documents[0].Layers[0].Pixels.Length);
+    }
+
+    [Fact]
+    public void RoundTrip_MultipleDocuments_PreservesAll()
+    {
+        var container = new MinintContainer(8, 8);
+        var doc1 = container.AddNewDocument("Frame1");
+        doc1.FrameDelayMs = 200;
+        var doc2 = container.AddNewDocument("Frame2");
+        doc2.FrameDelayMs = 500;
+
+        var result = RoundTrip(container);
+
+        Assert.Equal(2, result.Documents.Count);
+        Assert.Equal("Frame1", result.Documents[0].Name);
+        Assert.Equal(200u, result.Documents[0].FrameDelayMs);
+        Assert.Equal("Frame2", result.Documents[1].Name);
+        Assert.Equal(500u, result.Documents[1].FrameDelayMs);
+    }
+
+    [Fact]
+    public void RoundTrip_PaletteAndPixels_Preserved()
+    {
+        var container = new MinintContainer(4, 4);
+        var doc = container.AddNewDocument("Test");
+        var red = new RgbaColor(255, 0, 0, 255);
+        doc.EnsureColorCached(red);
+
+        var layer = doc.Layers[0];
+        layer.Pixels[0] = 1; // red
+
+        var result = RoundTrip(container);
+        var rdoc = result.Documents[0];
+
+        Assert.Equal(2, rdoc.Palette.Count); // transparent + red
+        Assert.Equal(RgbaColor.Transparent, rdoc.Palette[0]);
+        Assert.Equal(red, rdoc.Palette[1]);
+        Assert.Equal(1, rdoc.Layers[0].Pixels[0]);
+        Assert.Equal(0, rdoc.Layers[0].Pixels[1]);
+    }
+
+    [Fact]
+    public void RoundTrip_LayerProperties_Preserved()
+    {
+        var container = new MinintContainer(2, 2);
+        var doc = container.AddNewDocument("Test");
+        doc.Layers[0].Name = "Background";
+        doc.Layers[0].IsVisible = false;
+        doc.Layers[0].Opacity = 128;
+
+        var result = RoundTrip(container);
+        var layer = result.Documents[0].Layers[0];
+
+        Assert.Equal("Background", layer.Name);
+        Assert.False(layer.IsVisible);
+        Assert.Equal(128, layer.Opacity);
+    }
+
+    [Fact]
+    public void RoundTrip_LargePalette_Uses2ByteIndices()
+    {
+        var container = new MinintContainer(2, 2);
+        var doc = container.AddNewDocument("BigPalette");
+
+        for (int i = 0; i < 300; i++)
+            doc.EnsureColorCached(new RgbaColor((byte)(i % 256), (byte)(i / 256), 0, 255));
+
+        Assert.Equal(2, doc.IndexByteWidth);
+
+        int lastIdx = doc.Palette.Count - 1;
+        doc.Layers[0].Pixels[0] = lastIdx;
+
+        var result = RoundTrip(container);
+        Assert.Equal(lastIdx, result.Documents[0].Layers[0].Pixels[0]);
+    }
+
+    [Fact]
+    public void Read_InvalidSignature_Throws()
+    {
+        var ms = new MemoryStream("BADDATA"u8.ToArray());
+        Assert.Throws<InvalidDataException>(() => _serializer.Read(ms));
+    }
+
+    [Fact]
+    public void Read_TruncatedStream_Throws()
+    {
+        var ms = new MemoryStream("MINI"u8.ToArray());
+        Assert.Throws<InvalidDataException>(() => _serializer.Read(ms));
+    }
+
+    private MinintContainer RoundTrip(MinintContainer container)
+    {
+        var ms = new MemoryStream();
+        _serializer.Write(ms, container);
+        ms.Position = 0;
+        return _serializer.Read(ms);
+    }
+}

Minint.slnx

@@ -1,5 +1,6 @@
 <Solution>
   <Project Path="Minint.Core/Minint.Core.csproj" />
   <Project Path="Minint.Infrastructure/Minint.Infrastructure.csproj" />
+  <Project Path="Minint.Tests/Minint.Tests.csproj" />
   <Project Path="Minint/Minint.csproj" />
 </Solution>

Minint/Controls/PixelCanvas.cs

@@ -7,6 +7,8 @@ using Avalonia.Input;
 using Avalonia.Media;
 using Avalonia.Media.Imaging;
 using Avalonia.Threading;
+using Minint.Core.Models;
+using Minint.ViewModels;
 
 namespace Minint.Controls;
 
@@ -36,23 +38,30 @@ public class PixelCanvas : Control
 
     #region Events for tool interaction
 
-    /// <summary>Fires when the user presses the left mouse button at an image pixel.</summary>
     public event Action<int, int>? ToolDown;
-
-    /// <summary>Fires when the user drags with left button held at an image pixel.</summary>
     public event Action<int, int>? ToolDrag;
-
-    /// <summary>Fires when the cursor moves over the image (pixel coords, or null if outside).</summary>
     public event Action<(int X, int Y)?>? CursorPixelChanged;
-
-    /// <summary>Set by the host to provide preview mask pixels for overlay.</summary>
     public Func<List<(int X, int Y)>?>? GetPreviewMask { get; set; }
 
+    // Selection events
+    public event Action<int, int>? SelectionStart;
+    public event Action<int, int>? SelectionUpdate;
+    public event Action<int, int>? SelectionEnd;
+
+    // Paste events
+    public event Action<int, int>? PasteMoved;
+    public event Action? PasteCommitted;
+    public event Action? PasteCancelled;
+
+    /// <summary>Provides the current EditorViewModel for reading selection/paste state during render.</summary>
+    public EditorViewModel? Editor { get; set; }
+
     #endregion
 
     private readonly Viewport _viewport = new();
     private bool _isPanning;
     private bool _isDrawing;
+    private bool _isSelecting;
     private Point _panStart;
     private double _panStartOffsetX, _panStartOffsetY;
     private bool _viewportInitialized;
@@ -116,10 +125,12 @@ public class PixelCanvas : Control
         RenderOptions.SetBitmapInterpolationMode(this, BitmapInterpolationMode.None);
         context.DrawImage(bmp, srcRect, destRect);
 
-        if (ShowGrid && _viewport.Zoom >= 4)
+        if (ShowGrid)
             DrawPixelGrid(context, imgW, imgH);
 
         DrawToolPreview(context, imgW, imgH);
+        DrawSelectionOverlay(context);
+        DrawPastePreview(context);
 
         int w = imgW, h = imgH;
         Dispatcher.UIThread.Post(() => SyncScrollBars(w, h), DispatcherPriority.Render);
@@ -156,7 +167,11 @@ public class PixelCanvas : Control
 
     private void DrawPixelGrid(DrawingContext context, int imgW, int imgH)
     {
-        var pen = new Pen(new SolidColorBrush(Color.FromArgb(60, 255, 255, 255)), 1);
+        double zoom = _viewport.Zoom;
+        if (zoom < 4) return;
+
+        var pen = new Pen(Brushes.Black, 1);
+
         var clip = new Rect(0, 0, Bounds.Width, Bounds.Height);
         var imgRect = _viewport.ImageScreenRect(imgW, imgH);
         var visible = imgRect.Intersect(clip);
@@ -174,12 +189,14 @@ public class PixelCanvas : Control
             for (int px = startPx; px <= endPx; px++)
             {
                 var (sx, _) = _viewport.PixelToScreen(px, 0);
-                context.DrawLine(pen, new Point(sx, visible.Top), new Point(sx, visible.Bottom));
+                double x = Math.Floor(sx) + 0.5;
+                context.DrawLine(pen, new Point(x, visible.Top), new Point(x, visible.Bottom));
             }
             for (int py = startPy; py <= endPy; py++)
             {
                 var (_, sy) = _viewport.PixelToScreen(0, py);
-                context.DrawLine(pen, new Point(visible.Left, sy), new Point(visible.Right, sy));
+                double y = Math.Floor(sy) + 0.5;
+                context.DrawLine(pen, new Point(visible.Left, y), new Point(visible.Right, y));
             }
         }
     }
@@ -199,11 +216,9 @@ public class PixelCanvas : Control
             foreach (var (px, py) in mask)
             {
                 var (sx, sy) = _viewport.PixelToScreen(px, py);
-                var r = new Rect(sx, sy, zoom, zoom);
-                context.FillRectangle(previewBrush, r);
+                context.FillRectangle(previewBrush, new Rect(sx, sy, zoom, zoom));
             }
 
-            // Outline around the mask bounding box
             if (mask.Count > 0)
             {
                 int minX = mask[0].X, maxX = mask[0].X;
@@ -216,12 +231,63 @@ public class PixelCanvas : Control
                     if (py > maxY) maxY = py;
                 }
                 var (ox, oy) = _viewport.PixelToScreen(minX, minY);
-                var outlineRect = new Rect(ox, oy, (maxX - minX + 1) * zoom, (maxY - minY + 1) * zoom);
-                context.DrawRectangle(outlinePen, outlineRect);
+                context.DrawRectangle(outlinePen, new Rect(ox, oy, (maxX - minX + 1) * zoom, (maxY - minY + 1) * zoom));
             }
         }
     }
 
+    private void DrawSelectionOverlay(DrawingContext context)
+    {
+        var sel = Editor?.SelectionRectNormalized;
+        if (sel is null) return;
+
+        var (sx, sy, sw, sh) = sel.Value;
+        double zoom = _viewport.Zoom;
+        var (screenX, screenY) = _viewport.PixelToScreen(sx, sy);
+        var rect = new Rect(screenX, screenY, sw * zoom, sh * zoom);
+
+        var fillBrush = new SolidColorBrush(Color.FromArgb(40, 100, 150, 255));
+        context.FillRectangle(fillBrush, rect);
+
+        var borderPen = new Pen(new SolidColorBrush(Color.FromArgb(200, 100, 150, 255)), 1,
+            new DashStyle([4, 4], 0));
+        context.DrawRectangle(borderPen, rect);
+    }
+
+    private void DrawPastePreview(DrawingContext context)
+    {
+        if (Editor is null || !Editor.IsPasting || Editor.Clipboard is null)
+            return;
+
+        var pos = Editor.PastePosition!.Value;
+        var frag = Editor.Clipboard;
+        double zoom = _viewport.Zoom;
+
+        var clip = new Rect(0, 0, Bounds.Width, Bounds.Height);
+        using (context.PushClip(clip))
+        {
+            for (int fy = 0; fy < frag.Height; fy++)
+            {
+                for (int fx = 0; fx < frag.Width; fx++)
+                {
+                    var color = frag.Pixels[fy * frag.Width + fx];
+                    if (color.A == 0) continue;
+
+                    var (sx, sy) = _viewport.PixelToScreen(pos.X + fx, pos.Y + fy);
+                    byte dispA = (byte)(color.A * 180 / 255); // semi-transparent preview
+                    var brush = new SolidColorBrush(Color.FromArgb(dispA, color.R, color.G, color.B));
+                    context.FillRectangle(brush, new Rect(sx, sy, zoom, zoom));
+                }
+            }
+
+            // Border around the floating fragment
+            var (ox, oy) = _viewport.PixelToScreen(pos.X, pos.Y);
+            var borderPen = new Pen(new SolidColorBrush(Color.FromArgb(200, 255, 200, 50)), 1,
+                new DashStyle([3, 3], 0));
+            context.DrawRectangle(borderPen, new Rect(ox, oy, frag.Width * zoom, frag.Height * zoom));
+        }
+    }
+
     #endregion
 
     #region Scrollbar Sync
@@ -284,9 +350,6 @@ public class PixelCanvas : Control
         return (px, py);
     }
 
-    /// <summary>
-    /// Recalculates the pixel coordinate under the cursor after a viewport change.
-    /// </summary>
     private void RecalcCursorPixel()
     {
         if (_lastScreenPos is null) return;
@@ -341,17 +404,35 @@ public class PixelCanvas : Control
             _panStartOffsetX = _viewport.OffsetX;
             _panStartOffsetY = _viewport.OffsetY;
             e.Handled = true;
+            return;
         }
-        else if (props.IsLeftButtonPressed && !_isPanning)
+
+        if (!props.IsLeftButtonPressed || _isPanning) return;
+
+        var pixel = ScreenToPixelClamped(e.GetPosition(this));
+        if (pixel is null) return;
+
+        // Paste mode: left-click commits
+        if (Editor is not null && Editor.IsPasting)
         {
-            var pixel = ScreenToPixelClamped(e.GetPosition(this));
-            if (pixel is not null)
-            {
-                _isDrawing = true;
-                ToolDown?.Invoke(pixel.Value.X, pixel.Value.Y);
-                e.Handled = true;
-            }
+            PasteCommitted?.Invoke();
+            e.Handled = true;
+            return;
         }
+
+        // Select tool: begin rubber-band
+        if (Editor is not null && Editor.ActiveTool == ToolType.Select)
+        {
+            _isSelecting = true;
+            SelectionStart?.Invoke(pixel.Value.X, pixel.Value.Y);
+            e.Handled = true;
+            return;
+        }
+
+        // Regular drawing tools
+        _isDrawing = true;
+        ToolDown?.Invoke(pixel.Value.X, pixel.Value.Y);
+        e.Handled = true;
     }
 
     protected override void OnPointerMoved(PointerEventArgs e)
@@ -378,7 +459,24 @@ public class PixelCanvas : Control
         {
             _lastCursorPixel = pixel;
             CursorPixelChanged?.Invoke(pixel);
+        }
+
+        // Paste mode: floating fragment follows cursor
+        if (Editor is not null && Editor.IsPasting && pixel is not null)
+        {
+            PasteMoved?.Invoke(pixel.Value.X, pixel.Value.Y);
             InvalidateVisual();
+            e.Handled = true;
+            return;
+        }
+
+        // Selection rubber-band drag
+        if (_isSelecting && pixel is not null)
+        {
+            SelectionUpdate?.Invoke(pixel.Value.X, pixel.Value.Y);
+            InvalidateVisual();
+            e.Handled = true;
+            return;
         }
 
         if (_isDrawing && pixel is not null)
@@ -386,6 +484,10 @@ public class PixelCanvas : Control
             ToolDrag?.Invoke(pixel.Value.X, pixel.Value.Y);
             e.Handled = true;
         }
+        else
+        {
+            InvalidateVisual();
+        }
     }
 
     protected override void OnPointerReleased(PointerReleasedEventArgs e)
@@ -397,6 +499,15 @@ public class PixelCanvas : Control
             _isPanning = false;
             e.Handled = true;
         }
+        else if (_isSelecting && e.InitialPressMouseButton == MouseButton.Left)
+        {
+            _isSelecting = false;
+            var pixel = ScreenToPixelClamped(e.GetPosition(this));
+            if (pixel is not null)
+                SelectionEnd?.Invoke(pixel.Value.X, pixel.Value.Y);
+            InvalidateVisual();
+            e.Handled = true;
+        }
         else if (_isDrawing && e.InitialPressMouseButton == MouseButton.Left)
         {
             _isDrawing = false;
@@ -416,6 +527,33 @@ public class PixelCanvas : Control
         }
     }
 
+    protected override void OnKeyDown(KeyEventArgs e)
+    {
+        base.OnKeyDown(e);
+
+        if (e.Key == Key.Escape)
+        {
+            if (Editor is not null && Editor.IsPasting)
+            {
+                PasteCancelled?.Invoke();
+                InvalidateVisual();
+                e.Handled = true;
+            }
+            else if (Editor is not null && Editor.HasSelection)
+            {
+                Editor.ClearSelection();
+                InvalidateVisual();
+                e.Handled = true;
+            }
+        }
+        else if (e.Key == Key.Enter && Editor is not null && Editor.IsPasting)
+        {
+            PasteCommitted?.Invoke();
+            InvalidateVisual();
+            e.Handled = true;
+        }
+    }
+
     #endregion
 
     protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)

Minint/ViewModels/EditorViewModel.cs

@@ -5,6 +5,7 @@ using System.ComponentModel;
 using System.Linq;
 using Avalonia;
 using Avalonia.Media.Imaging;
+using Avalonia.Threading;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using Minint.Core.Models;
@@ -13,6 +14,11 @@ using Minint.Core.Services.Impl;
 
 namespace Minint.ViewModels;
 
+/// <summary>
+/// Palette-independent clipboard fragment: stores resolved RGBA pixels.
+/// </summary>
+public sealed record ClipboardFragment(int Width, int Height, RgbaColor[] Pixels);
+
 public partial class EditorViewModel : ViewModelBase
 {
     private readonly ICompositor _compositor = new Compositor();
@@ -66,6 +72,27 @@ public partial class EditorViewModel : ViewModelBase
 
     public RgbaColor SelectedColor => new(_previewColor.R, _previewColor.G, _previewColor.B, _previewColor.A);
 
+    // Selection state (Select tool rubber-band)
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(HasSelection))]
+    private (int X, int Y, int W, int H)? _selectionRect;
+
+    public bool HasSelection => SelectionRect is not null;
+
+    // Clipboard
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(HasClipboard))]
+    private ClipboardFragment? _clipboard;
+
+    public bool HasClipboard => Clipboard is not null;
+
+    // Paste mode
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(IsPasting))]
+    private (int X, int Y)? _pastePosition;
+
+    public bool IsPasting => PastePosition is not null;
+
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(Title))]
     private string? _filePath;
@@ -113,10 +140,6 @@ public partial class EditorViewModel : ViewModelBase
         SyncLayersAndCanvas(doc);
     }
 
-    /// <summary>
-    /// Re-syncs the Documents observable collection after an external modification
-    /// to Container.Documents (e.g. pattern generation adding a document).
-    /// </summary>
     public void SyncAfterExternalChange() => SyncDocumentsList();
 
     private void SyncDocumentsList()
@@ -191,7 +214,7 @@ public partial class EditorViewModel : ViewModelBase
     private void RemoveDocument()
     {
         if (Container is null || ActiveDocument is null) return;
-        if (Container.Documents.Count <= 1) return; // keep at least one
+        if (Container.Documents.Count <= 1) return;
 
         var doc = ActiveDocument;
         int idx = Container.Documents.IndexOf(doc);
@@ -203,10 +226,7 @@ public partial class EditorViewModel : ViewModelBase
     }
 
     [RelayCommand]
-    private void RenameDocument()
-    {
-        // Triggered via UI text edit — the Name property is directly editable via TextBox
-    }
+    private void RenameDocument() { }
 
     [RelayCommand]
     private void MoveDocumentUp()
@@ -254,7 +274,7 @@ public partial class EditorViewModel : ViewModelBase
     private void RemoveLayer()
     {
         if (ActiveDocument is null || ActiveLayer is null) return;
-        if (ActiveDocument.Layers.Count <= 1) return; // keep at least one
+        if (ActiveDocument.Layers.Count <= 1) return;
 
         UnsubscribeLayerVisibility();
         var layer = ActiveLayer;
@@ -322,6 +342,7 @@ public partial class EditorViewModel : ViewModelBase
 
     public void OnToolDown(int px, int py)
     {
+        if (IsPlaying) return;
         if (Container is null || ActiveDocument is null || ActiveLayer is null)
             return;
 
@@ -329,6 +350,8 @@ public partial class EditorViewModel : ViewModelBase
         if (px < 0 || px >= w || py < 0 || py >= h)
             return;
 
+        if (ActiveTool == ToolType.Select) return; // handled separately
+
         switch (ActiveTool)
         {
             case ToolType.Brush:
@@ -353,7 +376,8 @@ public partial class EditorViewModel : ViewModelBase
 
     public void OnToolDrag(int px, int py)
     {
-        if (ActiveTool == ToolType.Fill) return;
+        if (IsPlaying) return;
+        if (ActiveTool is ToolType.Fill or ToolType.Select) return;
         OnToolDown(px, py);
     }
 
@@ -361,7 +385,7 @@ public partial class EditorViewModel : ViewModelBase
     {
         if (PreviewCenter is null || Container is null)
             return null;
-        if (ActiveTool == ToolType.Fill)
+        if (ActiveTool is ToolType.Fill or ToolType.Select)
             return null;
 
         var (cx, cy) = PreviewCenter.Value;
@@ -369,36 +393,163 @@ public partial class EditorViewModel : ViewModelBase
     }
 
     [RelayCommand]
-    private void SelectBrush() => ActiveTool = ToolType.Brush;
+    private void SelectBrush() { CancelPasteMode(); ActiveTool = ToolType.Brush; }
 
     [RelayCommand]
-    private void SelectEraser() => ActiveTool = ToolType.Eraser;
+    private void SelectEraser() { CancelPasteMode(); ActiveTool = ToolType.Eraser; }
 
     [RelayCommand]
-    private void SelectFill() => ActiveTool = ToolType.Fill;
+    private void SelectFill() { CancelPasteMode(); ActiveTool = ToolType.Fill; }
+
+    [RelayCommand]
+    private void SelectSelectTool() { CancelPasteMode(); ActiveTool = ToolType.Select; }
 
     #endregion
 
-    #region Fragment copy (A4)
+    #region Selection + Copy/Paste (A4)
 
-    /// <summary>
-    /// Copies a rectangular fragment from <paramref name="srcDoc"/> active layer
-    /// to <paramref name="dstDoc"/> active layer.
-    /// </summary>
-    public void CopyFragment(
-        MinintDocument srcDoc, int srcLayerIndex,
-        int srcX, int srcY, int regionW, int regionH,
-        MinintDocument dstDoc, int dstLayerIndex,
-        int dstX, int dstY)
+    /// <summary>Called by PixelCanvas when selection drag starts.</summary>
+    public void BeginSelection(int px, int py)
     {
-        if (Container is null) return;
-        _fragmentService.CopyFragment(
-            srcDoc, srcLayerIndex, srcX, srcY, regionW, regionH,
-            dstDoc, dstLayerIndex, dstX, dstY,
-            Container.Width, Container.Height);
+        if (IsPlaying) return;
+        SelectionRect = (px, py, 0, 0);
+    }
+
+    /// <summary>Called by PixelCanvas as the user drags.</summary>
+    public void UpdateSelection(int px, int py)
+    {
+        if (SelectionRect is null) return;
+        var s = SelectionRect.Value;
+        int x = Math.Min(s.X, px);
+        int y = Math.Min(s.Y, py);
+        int w = Math.Abs(px - s.X) + 1;
+        int h = Math.Abs(py - s.Y) + 1;
+        // Store normalized rect but keep original anchor in _selAnchor
+        _selectionRectNormalized = (x, y, w, h);
+    }
+
+    /// <summary>Called by PixelCanvas when mouse is released.</summary>
+    public void FinishSelection(int px, int py)
+    {
+        if (SelectionRect is null) return;
+        var s = SelectionRect.Value;
+        int x0 = Math.Min(s.X, px);
+        int y0 = Math.Min(s.Y, py);
+        int rw = Math.Abs(px - s.X) + 1;
+        int rh = Math.Abs(py - s.Y) + 1;
+        if (Container is not null)
+        {
+            x0 = Math.Max(0, x0);
+            y0 = Math.Max(0, y0);
+            rw = Math.Min(rw, Container.Width - x0);
+            rh = Math.Min(rh, Container.Height - y0);
+        }
+        if (rw <= 0 || rh <= 0)
+        {
+            SelectionRect = null;
+            _selectionRectNormalized = null;
+            return;
+        }
+        SelectionRect = (x0, y0, rw, rh);
+        _selectionRectNormalized = SelectionRect;
+    }
+
+    private (int X, int Y, int W, int H)? _selectionRectNormalized;
+
+    /// <summary>The normalized (positive W/H, clamped) selection rectangle for rendering.</summary>
+    public (int X, int Y, int W, int H)? SelectionRectNormalized => _selectionRectNormalized;
+
+    [RelayCommand]
+    private void CopySelection()
+    {
+        if (SelectionRect is null || ActiveDocument is null || ActiveLayer is null || Container is null)
+            return;
+
+        var (sx, sy, sw, sh) = SelectionRect.Value;
+        int cw = Container.Width;
+        var palette = ActiveDocument.Palette;
+        var srcPixels = ActiveLayer.Pixels;
+        var buf = new RgbaColor[sw * sh];
+
+        for (int dy = 0; dy < sh; dy++)
+        {
+            int srcRow = sy + dy;
+            for (int dx = 0; dx < sw; dx++)
+            {
+                int srcCol = sx + dx;
+                int idx = srcPixels[srcRow * cw + srcCol];
+                buf[dy * sw + dx] = idx < palette.Count ? palette[idx] : RgbaColor.Transparent;
+            }
+        }
+
+        Clipboard = new ClipboardFragment(sw, sh, buf);
+    }
+
+    [RelayCommand]
+    private void PasteClipboard()
+    {
+        if (Clipboard is null) return;
+        PastePosition = (0, 0);
+    }
+
+    public void MovePaste(int px, int py)
+    {
+        if (IsPlaying || !IsPasting) return;
+        PastePosition = (px, py);
+    }
+
+    [RelayCommand]
+    public void CommitPaste()
+    {
+        if (IsPlaying) return;
+        if (!IsPasting || Clipboard is null || ActiveDocument is null || ActiveLayer is null || Container is null)
+            return;
+
+        var (px, py) = PastePosition!.Value;
+        int cw = Container.Width, ch = Container.Height;
+        var frag = Clipboard;
+        var dstPixels = ActiveLayer.Pixels;
+
+        for (int fy = 0; fy < frag.Height; fy++)
+        {
+            int dy = py + fy;
+            if (dy < 0 || dy >= ch) continue;
+            for (int fx = 0; fx < frag.Width; fx++)
+            {
+                int dx = px + fx;
+                if (dx < 0 || dx >= cw) continue;
+                var color = frag.Pixels[fy * frag.Width + fx];
+                if (color.A == 0) continue; // skip transparent
+                int colorIdx = ActiveDocument.EnsureColorCached(color);
+                dstPixels[dy * cw + dx] = colorIdx;
+            }
+        }
+
+        PastePosition = null;
+        SelectionRect = null;
+        _selectionRectNormalized = null;
         RefreshCanvas();
     }
 
+    [RelayCommand]
+    public void CancelPaste()
+    {
+        PastePosition = null;
+    }
+
+    public void ClearSelection()
+    {
+        SelectionRect = null;
+        _selectionRectNormalized = null;
+    }
+
+    private void CancelPasteMode()
+    {
+        PastePosition = null;
+        SelectionRect = null;
+        _selectionRectNormalized = null;
+    }
+
     #endregion
 
     #region Canvas rendering
@@ -457,6 +608,127 @@ public partial class EditorViewModel : ViewModelBase
 
     #endregion
 
+    #region Animation playback
+
+    private DispatcherTimer? _animationTimer;
+    private int _animationFrameIndex;
+
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(IsNotPlaying))]
+    private bool _isPlaying;
+
+    public bool IsNotPlaying => !IsPlaying;
+
+    [RelayCommand]
+    private void PlayAnimation()
+    {
+        if (Container is null || Container.Documents.Count < 2) return;
+        if (IsPlaying) return;
+
+        IsPlaying = true;
+        _animationFrameIndex = ActiveDocument is not null
+            ? Container.Documents.IndexOf(ActiveDocument)
+            : 0;
+        if (_animationFrameIndex < 0) _animationFrameIndex = 0;
+
+        AdvanceAnimationFrame();
+    }
+
+    [RelayCommand]
+    private void StopAnimation()
+    {
+        _animationTimer?.Stop();
+        _animationTimer = null;
+        IsPlaying = false;
+        if (ActiveDocument is not null)
+            SyncLayersAndCanvas(ActiveDocument);
+    }
+
+    private void AdvanceAnimationFrame()
+    {
+        if (Container is null || !IsPlaying)
+        {
+            StopAnimation();
+            return;
+        }
+
+        var docs = Container.Documents;
+        if (docs.Count == 0)
+        {
+            StopAnimation();
+            return;
+        }
+
+        _animationFrameIndex %= docs.Count;
+        var doc = docs[_animationFrameIndex];
+
+        _suppressDocumentSync = true;
+        ActiveDocument = doc;
+        _suppressDocumentSync = false;
+        RefreshCanvasFor(doc);
+
+        uint delay = doc.FrameDelayMs;
+        if (delay < 10) delay = 10;
+
+        _animationTimer?.Stop();
+        _animationTimer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(delay) };
+        _animationTimer.Tick += (_, _) =>
+        {
+            _animationTimer?.Stop();
+            _animationFrameIndex++;
+            AdvanceAnimationFrame();
+        };
+        _animationTimer.Start();
+    }
+
+    private void RefreshCanvasFor(MinintDocument doc)
+    {
+        if (Container is null)
+        {
+            CanvasBitmap = null;
+            return;
+        }
+
+        int w = Container.Width;
+        int h = Container.Height;
+        uint[] argb = _compositor.Composite(doc, w, h);
+
+        var bmp = new WriteableBitmap(
+            new PixelSize(w, h),
+            new Vector(96, 96),
+            Avalonia.Platform.PixelFormat.Bgra8888);
+
+        using (var fb = bmp.Lock())
+        {
+            unsafe
+            {
+                var dst = new Span<uint>((void*)fb.Address, w * h);
+                for (int i = 0; i < argb.Length; i++)
+                {
+                    uint px = argb[i];
+                    byte a2 = (byte)(px >> 24);
+                    byte r2 = (byte)((px >> 16) & 0xFF);
+                    byte g2 = (byte)((px >> 8) & 0xFF);
+                    byte b2 = (byte)(px & 0xFF);
+
+                    if (a2 == 255) { dst[i] = px; }
+                    else if (a2 == 0) { dst[i] = 0; }
+                    else
+                    {
+                        r2 = (byte)(r2 * a2 / 255);
+                        g2 = (byte)(g2 * a2 / 255);
+                        b2 = (byte)(b2 * a2 / 255);
+                        dst[i] = (uint)(b2 | (g2 << 8) | (r2 << 16) | (a2 << 24));
+                    }
+                }
+            }
+        }
+
+        CanvasBitmap = bmp;
+    }
+
+    #endregion
+
     public ICompositor Compositor => _compositor;
     public IPaletteService PaletteService => _paletteService;
     public IDrawingService DrawingService => _drawingService;

Minint/ViewModels/MainWindowViewModel.cs

@@ -1,6 +1,6 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
-using System.Linq;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Platform.Storage;
@@ -9,6 +9,7 @@ using CommunityToolkit.Mvvm.Input;
 using Minint.Core.Models;
 using Minint.Core.Services;
 using Minint.Core.Services.Impl;
+using Minint.Infrastructure.Export;
 using Minint.Infrastructure.Serialization;
 using Minint.Views;
 
@@ -19,12 +20,25 @@ public partial class MainWindowViewModel : ViewModelBase
     private readonly MinintSerializer _serializer = new();
     private readonly IImageEffectsService _effects = new ImageEffectsService();
     private readonly IPatternGenerator _patternGen = new PatternGenerator();
+    private readonly IBmpExporter _bmpExporter = new BmpExporter();
+    private readonly IGifExporter _gifExporter = new GifExporter();
+    private readonly ICompositor _compositor = new Compositor();
 
     private static readonly FilePickerFileType MinintFileType = new("Minint Files")
     {
         Patterns = ["*.minint"],
     };
 
+    private static readonly FilePickerFileType BmpFileType = new("BMP Image")
+    {
+        Patterns = ["*.bmp"],
+    };
+
+    private static readonly FilePickerFileType GifFileType = new("GIF Animation")
+    {
+        Patterns = ["*.gif"],
+    };
+
     [ObservableProperty]
     private EditorViewModel _editor = new();
 
@@ -36,10 +50,18 @@ public partial class MainWindowViewModel : ViewModelBase
     #region File commands
 
     [RelayCommand]
-    private void NewFile()
+    private async Task NewFileAsync()
     {
-        Editor.NewContainer(64, 64);
-        StatusText = "New 64×64 container created.";
+        if (Owner is not Window window) return;
+
+        var dialog = new NewContainerDialog();
+        var result = await dialog.ShowDialog<bool?>(window);
+        if (result != true) return;
+
+        int w = dialog.CanvasWidth;
+        int h = dialog.CanvasHeight;
+        Editor.NewContainer(w, h);
+        StatusText = $"New {w}×{h} container created.";
     }
 
     [RelayCommand]
@@ -153,49 +175,6 @@ public partial class MainWindowViewModel : ViewModelBase
 
     #endregion
 
-    #region Copy fragment (A4)
-
-    [RelayCommand]
-    private async Task CopyFragmentAsync()
-    {
-        if (Editor.Container is null || Owner is not Window window) return;
-
-        var docs = Editor.Container.Documents;
-        if (docs.Count == 0) return;
-
-        var dialog = new CopyFragmentDialog(docs, Editor.Container.Width, Editor.Container.Height);
-        var result = await dialog.ShowDialog<bool?>(window);
-        if (result != true) return;
-
-        if (dialog.SourceDocument is null || dialog.DestDocument is null)
-        {
-            StatusText = "Copy failed: no document selected.";
-            return;
-        }
-        if (dialog.SourceLayerIndex < 0 || dialog.DestLayerIndex < 0)
-        {
-            StatusText = "Copy failed: no layer selected.";
-            return;
-        }
-
-        try
-        {
-            Editor.CopyFragment(
-                dialog.SourceDocument, dialog.SourceLayerIndex,
-                dialog.SourceX, dialog.SourceY,
-                dialog.FragmentWidth, dialog.FragmentHeight,
-                dialog.DestDocument, dialog.DestLayerIndex,
-                dialog.DestX, dialog.DestY);
-            StatusText = $"Copied {dialog.FragmentWidth}×{dialog.FragmentHeight} fragment.";
-        }
-        catch (Exception ex)
-        {
-            StatusText = $"Copy failed: {ex.Message}";
-        }
-    }
-
-    #endregion
-
     #region Pattern generation (Б4)
 
     [RelayCommand]
@@ -229,4 +208,80 @@ public partial class MainWindowViewModel : ViewModelBase
     }
 
     #endregion
+
+    #region Export (BMP / GIF)
+
+    [RelayCommand]
+    private async Task ExportBmpAsync()
+    {
+        if (Editor.Container is null || Editor.ActiveDocument is null) return;
+        if (Owner?.StorageProvider is not { } sp) return;
+
+        var file = await sp.SaveFilePickerAsync(new FilePickerSaveOptions
+        {
+            Title = "Export document as BMP",
+            DefaultExtension = "bmp",
+            FileTypeChoices = [BmpFileType],
+            SuggestedFileName = $"{Editor.ActiveDocument.Name}.bmp",
+        });
+        if (file is null) return;
+
+        var path = file.TryGetLocalPath();
+        if (path is null) { StatusText = "Error: could not resolve file path."; return; }
+
+        try
+        {
+            int w = Editor.Container.Width, h = Editor.Container.Height;
+            uint[] argb = _compositor.Composite(Editor.ActiveDocument, w, h);
+            await using var fs = File.Create(path);
+            _bmpExporter.Export(fs, argb, w, h);
+            StatusText = $"Exported BMP: {Path.GetFileName(path)}";
+        }
+        catch (Exception ex)
+        {
+            StatusText = $"BMP export failed: {ex.Message}";
+        }
+    }
+
+    [RelayCommand]
+    private async Task ExportGifAsync()
+    {
+        if (Editor.Container is null || Editor.Container.Documents.Count == 0) return;
+        if (Owner?.StorageProvider is not { } sp) return;
+
+        var file = await sp.SaveFilePickerAsync(new FilePickerSaveOptions
+        {
+            Title = "Export animation as GIF",
+            DefaultExtension = "gif",
+            FileTypeChoices = [GifFileType],
+            SuggestedFileName = Editor.FilePath is not null
+                ? Path.GetFileNameWithoutExtension(Editor.FilePath) + ".gif"
+                : "animation.gif",
+        });
+        if (file is null) return;
+
+        var path = file.TryGetLocalPath();
+        if (path is null) { StatusText = "Error: could not resolve file path."; return; }
+
+        try
+        {
+            int w = Editor.Container.Width, h = Editor.Container.Height;
+            var frames = new List<(uint[] Pixels, uint DelayMs)>();
+            foreach (var doc in Editor.Container.Documents)
+            {
+                uint[] argb = _compositor.Composite(doc, w, h);
+                frames.Add((argb, doc.FrameDelayMs));
+            }
+
+            await using var fs = File.Create(path);
+            _gifExporter.Export(fs, frames, w, h);
+            StatusText = $"Exported GIF ({frames.Count} frames): {Path.GetFileName(path)}";
+        }
+        catch (Exception ex)
+        {
+            StatusText = $"GIF export failed: {ex.Message}";
+        }
+    }
+
+    #endregion
 }

Minint/ViewModels/ToolType.cs

@@ -4,5 +4,6 @@ public enum ToolType
 {
     Brush,
     Eraser,
-    Fill
+    Fill,
+    Select
 }

Minint/ViewModels/ToolTypeConverters.cs

@@ -13,6 +13,7 @@ public static class ToolTypeConverters
     public static readonly IValueConverter IsBrush = new ToolTypeConverter(ToolType.Brush);
     public static readonly IValueConverter IsEraser = new ToolTypeConverter(ToolType.Eraser);
     public static readonly IValueConverter IsFill = new ToolTypeConverter(ToolType.Fill);
+    public static readonly IValueConverter IsSelect = new ToolTypeConverter(ToolType.Select);
 
     private sealed class ToolTypeConverter(ToolType target) : IValueConverter
     {

Minint/Views/CopyFragmentDialog.axaml

@@ -1,51 +0,0 @@
-<Window xmlns="https://github.com/avaloniaui"
-        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        x:Class="Minint.Views.CopyFragmentDialog"
-        Title="Copy Fragment"
-        Width="380" Height="420"
-        WindowStartupLocation="CenterOwner"
-        CanResize="False"
-        SizeToContent="Height">
-    <StackPanel Margin="16" Spacing="8">
-        <TextBlock Text="Source" FontWeight="SemiBold"/>
-        <Grid ColumnDefinitions="100,*" RowDefinitions="Auto,Auto,Auto,Auto,Auto" RowSpacing="4" ColumnSpacing="8">
-            <TextBlock Grid.Row="0" Grid.Column="0" Text="Document:" VerticalAlignment="Center"/>
-            <ComboBox Grid.Row="0" Grid.Column="1" x:Name="SrcDocCombo"
-                      HorizontalAlignment="Stretch"/>
-            <TextBlock Grid.Row="1" Grid.Column="0" Text="Layer:" VerticalAlignment="Center"/>
-            <ComboBox Grid.Row="1" Grid.Column="1" x:Name="SrcLayerCombo"
-                      HorizontalAlignment="Stretch"/>
-            <TextBlock Grid.Row="2" Grid.Column="0" Text="X:" VerticalAlignment="Center"/>
-            <NumericUpDown Grid.Row="2" Grid.Column="1" x:Name="SrcX" Value="0" Minimum="0" FormatString="0"/>
-            <TextBlock Grid.Row="3" Grid.Column="0" Text="Y:" VerticalAlignment="Center"/>
-            <NumericUpDown Grid.Row="3" Grid.Column="1" x:Name="SrcY" Value="0" Minimum="0" FormatString="0"/>
-        </Grid>
-
-        <Grid ColumnDefinitions="100,*" RowDefinitions="Auto,Auto" RowSpacing="4" ColumnSpacing="8" Margin="0,4,0,0">
-            <TextBlock Grid.Row="0" Grid.Column="0" Text="Width:" VerticalAlignment="Center"/>
-            <NumericUpDown Grid.Row="0" Grid.Column="1" x:Name="RegionW" Value="16" Minimum="1" FormatString="0"/>
-            <TextBlock Grid.Row="1" Grid.Column="0" Text="Height:" VerticalAlignment="Center"/>
-            <NumericUpDown Grid.Row="1" Grid.Column="1" x:Name="RegionH" Value="16" Minimum="1" FormatString="0"/>
-        </Grid>
-
-        <Separator Margin="0,8"/>
-        <TextBlock Text="Destination" FontWeight="SemiBold"/>
-        <Grid ColumnDefinitions="100,*" RowDefinitions="Auto,Auto,Auto,Auto" RowSpacing="4" ColumnSpacing="8">
-            <TextBlock Grid.Row="0" Grid.Column="0" Text="Document:" VerticalAlignment="Center"/>
-            <ComboBox Grid.Row="0" Grid.Column="1" x:Name="DstDocCombo"
-                      HorizontalAlignment="Stretch"/>
-            <TextBlock Grid.Row="1" Grid.Column="0" Text="Layer:" VerticalAlignment="Center"/>
-            <ComboBox Grid.Row="1" Grid.Column="1" x:Name="DstLayerCombo"
-                      HorizontalAlignment="Stretch"/>
-            <TextBlock Grid.Row="2" Grid.Column="0" Text="X:" VerticalAlignment="Center"/>
-            <NumericUpDown Grid.Row="2" Grid.Column="1" x:Name="DstX" Value="0" Minimum="0" FormatString="0"/>
-            <TextBlock Grid.Row="3" Grid.Column="0" Text="Y:" VerticalAlignment="Center"/>
-            <NumericUpDown Grid.Row="3" Grid.Column="1" x:Name="DstY" Value="0" Minimum="0" FormatString="0"/>
-        </Grid>
-
-        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Spacing="8" Margin="0,12,0,0">
-            <Button Content="Copy" x:Name="OkButton" IsDefault="True" Padding="16,6"/>
-            <Button Content="Cancel" x:Name="CancelButton" IsCancel="True" Padding="16,6"/>
-        </StackPanel>
-    </StackPanel>
-</Window>

Minint/Views/CopyFragmentDialog.axaml.cs

@@ -1,91 +0,0 @@
-using System;
-using System.Collections.Generic;
-using Avalonia.Controls;
-using Avalonia.Interactivity;
-using Minint.Core.Models;
-
-namespace Minint.Views;
-
-public partial class CopyFragmentDialog : Window
-{
-    private readonly List<MinintDocument> _documents;
-
-    public MinintDocument? SourceDocument => SrcDocCombo.SelectedItem as MinintDocument;
-    public int SourceLayerIndex => SrcLayerCombo.SelectedIndex;
-    public int SourceX => (int)(SrcX.Value ?? 0);
-    public int SourceY => (int)(SrcY.Value ?? 0);
-    public int FragmentWidth => (int)(RegionW.Value ?? 1);
-    public int FragmentHeight => (int)(RegionH.Value ?? 1);
-    public MinintDocument? DestDocument => DstDocCombo.SelectedItem as MinintDocument;
-    public int DestLayerIndex => DstLayerCombo.SelectedIndex;
-    public int DestX => (int)(DstX.Value ?? 0);
-    public int DestY => (int)(DstY.Value ?? 0);
-
-    public CopyFragmentDialog()
-    {
-        _documents = [];
-        InitializeComponent();
-    }
-
-    public CopyFragmentDialog(List<MinintDocument> documents, int maxW, int maxH) : this()
-    {
-        _documents = documents;
-
-        SrcDocCombo.ItemsSource = documents;
-        SrcDocCombo.DisplayMemberBinding = new Avalonia.Data.Binding("Name");
-        DstDocCombo.ItemsSource = documents;
-        DstDocCombo.DisplayMemberBinding = new Avalonia.Data.Binding("Name");
-
-        SrcX.Maximum = maxW - 1;
-        SrcY.Maximum = maxH - 1;
-        DstX.Maximum = maxW - 1;
-        DstY.Maximum = maxH - 1;
-        RegionW.Maximum = maxW;
-        RegionH.Maximum = maxH;
-
-        if (documents.Count > 0)
-        {
-            SrcDocCombo.SelectedIndex = 0;
-            DstDocCombo.SelectedIndex = documents.Count > 1 ? 1 : 0;
-        }
-
-        SrcDocCombo.SelectionChanged += (_, _) => UpdateSrcLayers();
-        DstDocCombo.SelectionChanged += (_, _) => UpdateDstLayers();
-
-        UpdateSrcLayers();
-        UpdateDstLayers();
-
-        OkButton.Click += OnOkClick;
-        CancelButton.Click += OnCancelClick;
-    }
-
-    private void UpdateSrcLayers()
-    {
-        if (SrcDocCombo.SelectedItem is MinintDocument doc)
-        {
-            SrcLayerCombo.ItemsSource = doc.Layers;
-            SrcLayerCombo.DisplayMemberBinding = new Avalonia.Data.Binding("Name");
-            if (doc.Layers.Count > 0) SrcLayerCombo.SelectedIndex = 0;
-        }
-    }
-
-    private void UpdateDstLayers()
-    {
-        if (DstDocCombo.SelectedItem is MinintDocument doc)
-        {
-            DstLayerCombo.ItemsSource = doc.Layers;
-            DstLayerCombo.DisplayMemberBinding = new Avalonia.Data.Binding("Name");
-            if (doc.Layers.Count > 0) DstLayerCombo.SelectedIndex = 0;
-        }
-    }
-
-    private void OnOkClick(object? sender, RoutedEventArgs e)
-    {
-        Close(true);
-    }
-
-    private void OnCancelClick(object? sender, RoutedEventArgs e)
-    {
-        Close(false);
-    }
-}

Minint/Views/MainWindow.axaml

@@ -25,10 +25,19 @@
                 <Separator/>
                 <MenuItem Header="_Save" Command="{Binding SaveFileCommand}" HotKey="Ctrl+S"/>
                 <MenuItem Header="Save _As…" Command="{Binding SaveFileAsCommand}" HotKey="Ctrl+Shift+S"/>
+                <Separator/>
+                <MenuItem Header="Export Document as _BMP…" Command="{Binding ExportBmpCommand}"
+                          ToolTip.Tip="Export the active document as a 32-bit BMP file"/>
+                <MenuItem Header="Export All as _GIF…" Command="{Binding ExportGifCommand}"
+                          ToolTip.Tip="Export all documents as an animated GIF"/>
             </MenuItem>
             <MenuItem Header="_Edit">
-                <MenuItem Header="Copy _Fragment…" Command="{Binding CopyFragmentCommand}"
-                          ToolTip.Tip="Copy a rectangular region between documents"/>
+                <MenuItem Header="_Copy" Command="{Binding Editor.CopySelectionCommand}"
+                          HotKey="Ctrl+C"
+                          ToolTip.Tip="Copy the selected region to clipboard"/>
+                <MenuItem Header="_Paste" Command="{Binding Editor.PasteClipboardCommand}"
+                          HotKey="Ctrl+V"
+                          ToolTip.Tip="Paste clipboard fragment onto the canvas"/>
             </MenuItem>
             <MenuItem Header="_Image">
                 <MenuItem Header="Adjust _Contrast…" Command="{Binding ApplyContrastCommand}"
@@ -41,7 +50,7 @@
             </MenuItem>
             <MenuItem Header="_View">
                 <MenuItem Header="Pixel _Grid" ToggleType="CheckBox"
-                          IsChecked="{Binding Editor.ShowGrid}" HotKey="Ctrl+G"/>
+                          IsChecked="{Binding Editor.ShowGrid, Mode=TwoWay}" HotKey="Ctrl+G"/>
             </MenuItem>
         </Menu>
 
@@ -62,6 +71,10 @@
                              ToolTip.Tip="Fill tool — flood fill with selected color"
                              IsChecked="{Binding Editor.ActiveTool, Converter={x:Static vm:ToolTypeConverters.IsFill}}"
                              Command="{Binding Editor.SelectFillCommand}"/>
+                <RadioButton GroupName="Tool" Content="Select"
+                             ToolTip.Tip="Select tool — drag to select a region, then Copy/Paste"
+                             IsChecked="{Binding Editor.ActiveTool, Converter={x:Static vm:ToolTypeConverters.IsSelect}}"
+                             Command="{Binding Editor.SelectSelectToolCommand}"/>
 
                 <Separator/>
 
@@ -77,7 +90,7 @@
                 <TextBlock Text="Color:" VerticalAlignment="Center"/>
                 <ColorPicker x:Name="ToolColorPicker"
                              Color="{Binding Editor.PreviewColor, Mode=TwoWay}"
-                             IsAlphaVisible="False"
+                             IsAlphaVisible="True"
                              VerticalAlignment="Center"/>
             </StackPanel>
         </Border>
@@ -96,6 +109,31 @@
                     BorderThickness="0,0,1,0" Padding="4">
                 <DockPanel>
                     <TextBlock DockPanel.Dock="Top" Text="Documents" FontWeight="SemiBold" Margin="0,0,0,4"/>
+
+                    <!-- Animation controls -->
+                    <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" Spacing="4" Margin="0,4,0,0">
+                        <Button Content="▶" ToolTip.Tip="Play animation"
+                                Command="{Binding Editor.PlayAnimationCommand}"
+                                IsEnabled="{Binding Editor.IsNotPlaying}" Padding="6,2"/>
+                        <Button Content="■" ToolTip.Tip="Stop animation"
+                                Command="{Binding Editor.StopAnimationCommand}"
+                                IsEnabled="{Binding Editor.IsPlaying}" Padding="6,2"/>
+                    </StackPanel>
+
+                    <!-- Frame delay -->
+                    <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" Spacing="4" Margin="0,4,0,0">
+                        <TextBlock Text="Delay:" VerticalAlignment="Center" FontSize="12"/>
+                        <NumericUpDown Value="{Binding Editor.ActiveDocument.FrameDelayMs}"
+                                       Minimum="10" Maximum="10000" Increment="10"
+                                       FormatString="0"
+                                       Width="110" FontSize="12"
+                                       ToolTip.Tip="Frame delay in milliseconds"
+                                       VerticalAlignment="Center"
+                                       Foreground="{DynamicResource SystemControlForegroundBaseHighBrush}"/>
+                        <TextBlock Text="ms" VerticalAlignment="Center" FontSize="12"/>
+                    </StackPanel>
+
+                    <!-- Document management buttons -->
                     <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" Spacing="2" Margin="0,4,0,0">
                         <Button Content="+" ToolTip.Tip="Add a new document (frame)"
                                 Command="{Binding Editor.AddDocumentCommand}" Padding="6,2"/>

Minint/Views/MainWindow.axaml.cs

@@ -37,9 +37,19 @@ public partial class MainWindow : Window
 
     private static void WireCanvasEvents(PixelCanvas canvas, EditorViewModel editor)
     {
+        canvas.Editor = editor;
+
         canvas.ToolDown += (px, py) => editor.OnToolDown(px, py);
         canvas.ToolDrag += (px, py) => editor.OnToolDrag(px, py);
         canvas.CursorPixelChanged += pixel => editor.PreviewCenter = pixel;
         canvas.GetPreviewMask = () => editor.GetPreviewMask();
+
+        canvas.SelectionStart += (px, py) => editor.BeginSelection(px, py);
+        canvas.SelectionUpdate += (px, py) => editor.UpdateSelection(px, py);
+        canvas.SelectionEnd += (px, py) => { editor.FinishSelection(px, py); canvas.InvalidateVisual(); };
+
+        canvas.PasteMoved += (px, py) => editor.MovePaste(px, py);
+        canvas.PasteCommitted += () => { editor.CommitPaste(); canvas.InvalidateVisual(); };
+        canvas.PasteCancelled += () => { editor.CancelPaste(); canvas.InvalidateVisual(); };
     }
 }

Minint/Views/NewContainerDialog.axaml

@@ -0,0 +1,31 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="Minint.Views.NewContainerDialog"
+        Title="New Container"
+        Width="300"
+        WindowStartupLocation="CenterOwner"
+        CanResize="False"
+        SizeToContent="Height">
+    <StackPanel Margin="16" Spacing="12">
+        <TextBlock Text="Canvas size:" FontWeight="SemiBold"/>
+
+        <Grid ColumnDefinitions="Auto,*" RowDefinitions="Auto,Auto" RowSpacing="8" ColumnSpacing="8">
+            <TextBlock Grid.Row="0" Grid.Column="0" Text="Width:" VerticalAlignment="Center"/>
+            <NumericUpDown Grid.Row="0" Grid.Column="1"
+                           x:Name="WidthInput"
+                           Value="64" Minimum="1" Maximum="4096" Increment="1"
+                           FormatString="0"/>
+
+            <TextBlock Grid.Row="1" Grid.Column="0" Text="Height:" VerticalAlignment="Center"/>
+            <NumericUpDown Grid.Row="1" Grid.Column="1"
+                           x:Name="HeightInput"
+                           Value="64" Minimum="1" Maximum="4096" Increment="1"
+                           FormatString="0"/>
+        </Grid>
+
+        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Spacing="8" Margin="0,8,0,0">
+            <Button Content="Create" x:Name="OkButton" IsDefault="True" Padding="16,6"/>
+            <Button Content="Cancel" x:Name="CancelButton" IsCancel="True" Padding="16,6"/>
+        </StackPanel>
+    </StackPanel>
+</Window>

Minint/Views/NewContainerDialog.axaml.cs

@@ -0,0 +1,17 @@
+using Avalonia.Controls;
+
+namespace Minint.Views;
+
+public partial class NewContainerDialog : Window
+{
+    public int CanvasWidth => (int)(WidthInput.Value ?? 64);
+    public int CanvasHeight => (int)(HeightInput.Value ?? 64);
+
+    public NewContainerDialog()
+    {
+        InitializeComponent();
+
+        OkButton.Click += (_, _) => Close(true);
+        CancelButton.Click += (_, _) => Close(false);
+    }
+}

Minint/Views/PatternDialog.axaml

@@ -2,10 +2,12 @@
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         x:Class="Minint.Views.PatternDialog"
         Title="Generate Pattern"
-        Width="360"
+        Width="640"
+        Height="520"
+        MinWidth="480"
+        MinHeight="400"
         WindowStartupLocation="CenterOwner"
-        CanResize="False"
-        SizeToContent="Height">
+        CanResize="True">
     <StackPanel Margin="16" Spacing="8">
         <Grid ColumnDefinitions="100,*" RowDefinitions="Auto,Auto,Auto,Auto,Auto,Auto" RowSpacing="6" ColumnSpacing="8">
             <TextBlock Grid.Row="0" Grid.Column="0" Text="Pattern:" VerticalAlignment="Center"/>

README.md

@@ -0,0 +1,94 @@
+# Minint
+
+> Растровый редактор с собственным бинарным форматом `.minint`, поддержкой слоёв, анимации и палитровых эффектов.
+
+## Что это
+
+Desktop-приложение для создания и редактирования пиксельной графики. Изображения хранятся в собственном бинарном формате с палитровой моделью, где каждый документ (кадр) содержит свою палитру RGBA и набор слоёв. Контейнер объединяет несколько документов для анимации.
+
+## Возможности
+
+- **Собственный формат `.minint`** — самописная бинарная сериализация с валидацией, переменным размером индексов палитры (1–4 байта)
+- **Слои** — добавление, удаление, переименование, порядок, видимость, прозрачность, дублирование
+- **Документы/кадры** — несколько документов в одном контейнере, каждый со своей палитрой
+- **Инструменты** — кисть, ластик (с регулируемым радиусом), заливка (flood fill), выделение + копирование/вставка
+- **Холст** — pan (среднее колёсико / touchpad), zoom (Ctrl+колёсико), nearest-neighbor масштабирование, пиксельная сетка
+- **Эффекты** — контрастность (A1), перевод в градации серого (A2) — применяются через палитру
+- **Копирование фрагмента (A4)** — визуальное выделение на холсте, плавающая вставка с поддержкой смены документа/слоя
+- **Генерация узоров (Б4)** — шахматка, градиент, полосы, концентрические круги, плитка
+- **Анимация** — проигрывание документов как кадров с настраиваемым delay
+- **Экспорт** — BMP (32-bit BGRA, самописный), GIF (анимированный, LZW, самописный)
+
+## Стек
+
+| Компонент | Технология |
+|-----------|------------|
+| Язык | C# / .NET 10 |
+| UI | Avalonia 11.3.8 |
+| MVVM | CommunityToolkit.Mvvm 8.2.1 |
+| Тесты | xUnit |
+| Сериализация | Полностью самописная (бинарная) |
+| Экспорт BMP/GIF | Полностью самописный |
+
+## Структура проекта
+
+```
+Minint.slnx
+├── Minint.Core/          — Доменные модели, интерфейсы сервисов, чистая логика
+├── Minint.Infrastructure/ — Сериализация .minint, экспорт BMP/GIF
+├── Minint/                — Avalonia UI приложение
+└── Minint.Tests/          — Unit-тесты (xUnit)
+```
+
+Core не зависит ни от каких внешних пакетов. Infrastructure зависит только от Core. UI зависит от Core + Infrastructure + Avalonia.
+
+## Требования
+
+- [.NET 10 SDK](https://dotnet.microsoft.com/download) или новее
+
+## Сборка и запуск
+
+```bash
+dotnet build
+dotnet run --project Minint
+```
+
+## Тесты
+
+```bash
+dotnet test
+```
+
+37 тестов покрывают: сериализацию (round-trip), композитинг, инструменты рисования, flood fill, эффекты (контраст, grayscale), генерацию паттернов, копирование фрагмента, экспорт BMP/GIF.
+
+## Управление
+
+| Действие | Управление |
+|----------|------------|
+| Зум | Ctrl + колёсико мыши |
+| Перемещение (pan) | Среднее колёсико / touchpad scroll |
+| Рисование | Левая кнопка мыши |
+| Пиксельная сетка | Ctrl+G или View > Pixel Grid |
+| Копирование фрагмента | Select tool → выделить → Ctrl+C → Ctrl+V → кликнуть для фиксации |
+| Отмена вставки | Escape |
+| Новый файл | Ctrl+N |
+| Открыть | Ctrl+O |
+| Сохранить | Ctrl+S |
+
+## Формат `.minint`
+
+Подробная спецификация формата — в файле [`FORMAT.md`](FORMAT.md).
+
+Ключевые свойства:
+- Little-endian
+- Сигнатура `MININT`, версия формата
+- Палитра RGBA на документ, индексы переменной ширины (1–4 байта)
+- Полная валидация при чтении
+
+## Ограничения
+
+- **Undo/Redo** не реализовано (архитектура не запрещает добавление)
+- **Размер контейнера** — все документы имеют одинаковые размеры (width × height на уровне контейнера)
+- **GIF квантизация** — простая popularity-based (до 256 цветов), может терять оттенки
+- **Максимальный размер** — 65536 × 65536 пикселей (ограничение формата)
+- Имена документов/слоёв — максимум 255 UTF-8 байт