Этап 2

Minint.Core/Services/IDrawingService.cs

@@ -0,0 +1,25 @@
+using Minint.Core.Models;
+
+namespace Minint.Core.Services;
+
+public interface IDrawingService
+{
+    /// <summary>
+    /// Applies a circular brush stroke at (<paramref name="cx"/>, <paramref name="cy"/>)
+    /// with the given <paramref name="radius"/>. Sets affected pixels to <paramref name="colorIndex"/>.
+    /// </summary>
+    void ApplyBrush(MinintLayer layer, int cx, int cy, int radius, int colorIndex, int width, int height);
+
+    /// <summary>
+    /// Applies a circular eraser at (<paramref name="cx"/>, <paramref name="cy"/>)
+    /// with the given <paramref name="radius"/>. Sets affected pixels to index 0 (transparent).
+    /// </summary>
+    void ApplyEraser(MinintLayer layer, int cx, int cy, int radius, int width, int height);
+
+    /// <summary>
+    /// Returns the set of pixel coordinates affected by a circular brush/eraser
+    /// centered at (<paramref name="cx"/>, <paramref name="cy"/>) with given <paramref name="radius"/>.
+    /// Used for tool preview overlay.
+    /// </summary>
+    List<(int X, int Y)> GetBrushMask(int cx, int cy, int radius, int width, int height);
+}