Fur als 4. Paint-Map + Ziel-Opacity-Blend

Fur wird die vierte kanonische Paint-Map (RGB=Farbe, A=Länge). Integration
über Seed (kahl), GPU/CPU-Paint, Undo, Netzwerk-Sync, Persistence (fur.png,
v6) und Live-RT-Hook im FurShellRenderer. HUD-Binding (Toggle/Picker/Alpha)
aktiviert. Fur-Alpha lerpt jetzt zu einer Ziel-Opacity (Slider_FurOpacity)
statt additiv Richtung 1 zu akkumulieren (zwei Brush-Passes: Fade + Deposit).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/Components/MeshPainter/MeshPainter.Cpu.cs

@@ -36,7 +36,9 @@ public partial class MeshPainter
     {
         var src = ResolveSeed(mi, canonical);
         var px = (Color32[])src.Clone();
-        if (mi != MAP_MSO) // albedo / emission: opaque. The mask map keeps alpha = smoothness.
+        // Albedo / emission are opaque. The mask map keeps alpha = smoothness; fur keeps alpha = painted
+        // length (0 = bald), which is data, not coverage.
+        if (mi != MAP_MSO && mi != MAP_FUR)
             for (int i = 0; i < px.Length; i++) px[i].a = 255;
         return px;
     }
@@ -66,7 +68,9 @@ public partial class MeshPainter
         {
             if (!IsChannelActive(mi)) continue;
             var cm = _cpu[mi];
-            if (paddingTexels > 0) DilatePadding(cm, paddingTexels);
+            // Fur skips edge padding: its alpha is length, not a coverage guard, so there is no valid
+            // dilation source mask (matches the GPU path, which also skips fur in EndGpuStroke).
+            if (paddingTexels > 0 && mi != MAP_FUR) DilatePadding(cm, paddingTexels);
             FlushDirty(cm);
         }
     }
@@ -98,8 +102,8 @@ public partial class MeshPainter
     /// </summary>
     private void PaintStamp3D(Vector3 pLocal, float radiusLocal, Vector3 u, Vector3 v, Vector3 n)
     {
-        bool aAlb = paintAlbedo, aMS = paintMetallicSmoothness, aEM = paintEmission, aAO = paintOcclusion;
-        if (!aAlb && !aMS && !aEM && !aAO) return;
+        bool aAlb = paintAlbedo, aMS = paintMetallicSmoothness, aEM = paintEmission, aAO = paintOcclusion, aFur = fur;
+        if (!aAlb && !aMS && !aEM && !aAO && !aFur) return;
 
         // Albedo target (brush color in linear space; blended linear to match the GPU).
         float brLin = Mathf.GammaToLinearSpace(brushColor.r);
@@ -125,6 +129,15 @@ public partial class MeshPainter
         float emOpMul = Mathf.Clamp01(emissionColor.a);
         CpuMap em = _cpu[MAP_EM];
 
+        // Fur target (linear RGB like albedo; alpha = painted length that EASES toward furTargetA
+        // at the brush strength furColor.a, not accumulating to full - mirrors the GPU fade+deposit).
+        float frLin = Mathf.GammaToLinearSpace(furColor.r);
+        float fgLin = Mathf.GammaToLinearSpace(furColor.g);
+        float fbLin = Mathf.GammaToLinearSpace(furColor.b);
+        float furOpMul = Mathf.Clamp01(furColor.a);
+        float furTargetA = Mathf.Clamp01(furOpacity) * 255f;
+        CpuMap furm = _cpu[MAP_FUR];
+
         float invR = 1f / radiusLocal;
         int triCount = _tris.Length / 3;
         float ts = textureSize;
@@ -243,6 +256,27 @@ public partial class MeshPainter
                         }
                     }
 
+                    if (aFur)
+                    {
+                        float op = maskOp * furOpMul;
+                        if (op > 0f)
+                        {
+                            Color32 dst = furm.pixels[idx];
+                            float it = 1f - op;
+                            // RGB source-over toward the fur colour (linear); alpha EASES toward the target
+                            // length at the deposit rate: lerp(dst.a, target, op) - over-writable, not
+                            // accumulating. Mirrors the GPU fur fade (alpha *= 1-op) + deposit (+= op*target).
+                            byte na = (byte)(dst.a * it + furTargetA * op + 0.5f);
+                            furm.pixels[idx] = new Color32(
+                                BlendSrgb(dst.r, frLin, it, op),
+                                BlendSrgb(dst.g, fgLin, it, op),
+                                BlendSrgb(dst.b, fbLin, it, op),
+                                na);
+                            furm.painted[idx] = true;
+                            ExpandDirty(furm, x, y);
+                        }
+                    }
+
                 }
             }
         }