From 36bfe5ad45b97234b546f16ed523f7b69491f348 Mon Sep 17 00:00:00 2001
From: Heller <heller@nullptr.top>
Date: Fri, 19 Jun 2026 10:22:33 +0000
Subject: [PATCH] fix: tail as full body segment + fading ghost for smooth
 illusion

Tail is now part of the main body path (grid-snapped, full thickness,
sharp corners). Smooth movement illusion via fading ghost circle at
the old tail position that fades out during the tick.
---
 Snake.Avalonia/Views/SnakeRenderer.cs | 68 ++++++++++-----------------
 1 file changed, 25 insertions(+), 43 deletions(-)

diff --git a/Snake.Avalonia/Views/SnakeRenderer.cs b/Snake.Avalonia/Views/SnakeRenderer.cs
index 92d7cd6..06af464 100644
--- a/Snake.Avalonia/Views/SnakeRenderer.cs
+++ b/Snake.Avalonia/Views/SnakeRenderer.cs
@@ -135,21 +135,21 @@ public sealed class SnakeRenderer : Control
         var segmentsList = Segments;
         var count = segmentsList.Count;
 
-        // === Body path: from segment[Count-2] down to segment[0] ===
-        // Build with grid-snapped middle segments → sharp corners.
-        // The tail (segment[Count-1]) is excluded and drawn separately below.
+        // === Body path: from segment[Count-1] (tail) through segment[0] (head) ===
+        // All segments use GetVisualPosition — middle/body returns grid-snapped,
+        // head returns interpolated. Tail is grid-snapped, giving sharp corners
+        // with full body thickness.
         if (count >= 2)
         {
             var bodyGeometry = new StreamGeometry();
             using (var ctx = bodyGeometry.Open())
             {
-                // Start at second-to-last segment (grid-snapped for count>2,
-                // head-interpolated for count==2 — harmless since it's just the head)
-                var (startX, startY) = GetVisualPosition(segmentsList[count - 2], count - 2, t);
+                // Start at tail (last segment, grid-snapped)
+                var (startX, startY) = GetVisualPosition(segmentsList[count - 1], count - 1, t);
                 ctx.BeginFigure(new Point(startX, startY), false);
 
                 // Draw through middle segments down to head
-                for (var i = count - 3; i >= 0; i--)
+                for (var i = count - 2; i >= 0; i--)
                 {
                     var (px, py) = GetVisualPosition(segmentsList[i], i, t);
                     ctx.LineTo(new Point(px, py));
@@ -172,30 +172,26 @@ public sealed class SnakeRenderer : Control
             context.DrawGeometry(null, innerPen, bodyGeometry);
         }
 
-        // === Tail: separate fading line from interpolated tail to body ===
-        if (count >= 2)
+        // === Fading ghost circle at old tail position ===
+        // Creates the illusion of smooth tail movement without affecting
+        // the body path geometry (which stays grid-snapped with sharp corners).
+        if (count >= 2 && PreviousSegments != null && PreviousSegments.Count > 0)
         {
-            var (tailX, tailY) = GetVisualPosition(segmentsList[count - 1], count - 1, t);
-            var (bodyEndX, bodyEndY) = GetVisualPosition(segmentsList[count - 2], count - 2, t);
+            var opacity = 0.4 * (1.0 - t);
+            if (opacity > 0)
+            {
+                var oldTailPos = PreviousSegments[PreviousSegments.Count - 1];
+                var currentTailPos = segmentsList[count - 1];
 
-            // Fading tail line — thinner and semi-transparent
-            var tailThickness = CellSize * 0.35;
-            var tailPen = new Pen(
-                new SolidColorBrush(SnakeTailBrush.Color, 0.5),
-                tailThickness,
-                lineCap: PenLineCap.Round,
-                lineJoin: PenLineJoin.Round);
-            context.DrawLine(tailPen,
-                new Point(tailX, tailY),
-                new Point(bodyEndX, bodyEndY));
+                var (ghostX, ghostY) = AnimationHelper.InterpolatePosition(
+                    oldTailPos, currentTailPos, t, CellSize, useEasing: false);
 
-            // Soft fading ellipse at the interpolated tail tip
-            var fadeRadius = tailThickness * 0.8;
-            context.DrawEllipse(
-                new SolidColorBrush(SnakeTailBrush.Color, 0.3),
-                null,
-                new Point(tailX, tailY),
-                fadeRadius, fadeRadius);
+                context.DrawEllipse(
+                    new SolidColorBrush(SnakeBodyBrush.Color, opacity),
+                    null,
+                    new Point(ghostX, ghostY),
+                    CellSize * 0.35, CellSize * 0.35);
+            }
         }
 
         // Draw head
@@ -393,21 +389,7 @@ public sealed class SnakeRenderer : Control
             return AnimationHelper.InterpolatePosition(from, pos, t, CellSize, useEasing: true);
         }
 
-        // Tail (last segment, only when there are multiple segments): interpolated LINEARLY
-        // This is used ONLY in the separate tail-drawing code, not in the main body path,
-        // so it does NOT create diagonal shortcuts at corners.
-        // The tail line connects from this interpolated position to the grid-snapped
-        // second-to-last segment.
-        if (Segments != null && Segments.Count > 1 && segmentIndex == Segments.Count - 1)
-        {
-            var from = PreviousSegments != null && PreviousSegments.Count > 0
-                ? AnimationHelper.GetPreviousPosition(segmentIndex, Segments!, PreviousSegments, SnakeDirection)
-                : pos;
-
-            return AnimationHelper.InterpolatePosition(from, pos, t, CellSize, useEasing: false);
-        }
-
-        // Middle segments: grid-snapped for sharp corners
+        // All other segments (body and tail): grid-snapped for sharp corners
         return (pos.X * CellSize + CellSize * 0.5, pos.Y * CellSize + CellSize * 0.5);
     }
 }