Initial commit: Unity mesh painter project

Unity 6000.3 (URP) project with live mesh painting in play mode.

- MeshPainter.cs: paint a SkinnedMesh with the mouse, seamless across
  UV islands via 3D-space painting, GPU and CPU backends (switchable),
  edge-padding/dilation against bilinear seam bleed
- FrameRateLimiter.cs: simple frame rate limiting component
- MeshPaintBrush / MeshPaintDilate shaders for the GPU paint path
- Unity-specific .gitignore and .gitattributes

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

Assets/Shaders/MeshPaintBrush.shader

@@ -0,0 +1,74 @@
+// GPU brush: paints a 3D sphere seamlessly into the paint texture.
+//
+// In the vertex shader the mesh is "unwrapped" into the texture layout using its
+// UVs (uv -> clip space), while the actual local 3D position of the vertex is
+// passed through to the fragment shader. There, per texel, the distance to the
+// brush center (_BrushCenter, in local mesh space) is tested against _BrushRadius.
+//
+// This bridges UV seams automatically: triangles on both sides of a seam share
+// the same 3D edge and are captured by the same brush stroke, no matter where
+// they lie in the UV layout (identical behavior to the CPU path).
+Shader "Hidden/MeshPaintBrush"
+{
+    Properties
+    {
+        _BrushColor ("Brush Color", Color) = (1,0,0,1)
+    }
+    SubShader
+    {
+        Tags { "RenderType" = "Opaque" }
+        Pass
+        {
+            ZTest Always
+            ZWrite Off
+            Cull Off
+            Blend Off
+
+            CGPROGRAM
+            #pragma vertex vert
+            #pragma fragment frag
+            #include "UnityCG.cginc"
+
+            float4 _BrushColor;
+            float3 _BrushCenter;   // brush center in local mesh space
+            float  _BrushRadius;   // brush radius in local mesh space
+
+            struct appdata
+            {
+                float4 vertex : POSITION;   // local 3D position
+                float2 uv     : TEXCOORD0;  // UV (target in the texture layout)
+            };
+
+            struct v2f
+            {
+                float4 pos   : SV_POSITION;
+                float3 local : TEXCOORD0;   // interpolated local 3D position
+            };
+
+            v2f vert (appdata v)
+            {
+                v2f o;
+                // UV (0..1) -> clip space (-1..1). This makes the GPU rasterize
+                // each triangle exactly at its place in the texture.
+                float2 p = v.uv * 2.0 - 1.0;
+                #if UNITY_UV_STARTS_AT_TOP
+                    p.y = -p.y; // compensate the RenderTexture Y-flip (D3D etc.)
+                #endif
+                o.pos = float4(p, 0.0, 1.0);
+                o.local = v.vertex.xyz;
+                return o;
+            }
+
+            fixed4 frag (v2f i) : SV_Target
+            {
+                // Only color texels inside the 3D brush sphere.
+                float d = distance(i.local, _BrushCenter);
+                clip(_BrushRadius - d);
+                // Alpha = 1 marks "painted by the brush" (source for the edge padding).
+                return fixed4(_BrushColor.rgb, 1.0);
+            }
+            ENDCG
+        }
+    }
+    Fallback Off
+}

Assets/Shaders/MeshPaintBrush.shader.meta

@@ -0,0 +1,9 @@
+fileFormatVersion: 2
+guid: cfff45d9ec693b247909d39c182922ff
+ShaderImporter:
+  externalObjects: {}
+  defaultTextures: []
+  nonModifiableTextures: []
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Shaders/MeshPaintDilate.shader

@@ -0,0 +1,72 @@
+// GPU edge padding / texture dilation against visible UV seams.
+//
+// Between the UV islands there is an unpainted border (gutter). During bilinear
+// sampling at an island edge, the GPU mixes the painted edge with the unpainted
+// base color -> bright seam lines. This pass "bleeds" the painted color up to
+// _Pad texels beyond the island edges.
+//
+// The dilation source is exclusively painted texels (alpha >= 0.5). The padding
+// texels produced get alpha = 0 -> next frame they are NO LONGER a source, so the
+// padding does not grow unbounded (it stays at _Pad texels).
+Shader "Hidden/MeshPaintDilate"
+{
+    Properties
+    {
+        _MainTex ("Texture", 2D) = "white" {}
+    }
+    SubShader
+    {
+        Tags { "RenderType" = "Opaque" }
+        Pass
+        {
+            ZTest Always
+            ZWrite Off
+            Cull Off
+            Blend Off
+
+            CGPROGRAM
+            #pragma vertex vert_img
+            #pragma fragment frag
+            #include "UnityCG.cginc"
+
+            sampler2D _MainTex;
+            float4 _MainTex_TexelSize; // (1/w, 1/h, w, h)
+            int _Pad;
+
+            #define MAXPAD 16
+
+            fixed4 frag (v2f_img i) : SV_Target
+            {
+                fixed4 c = tex2D(_MainTex, i.uv);
+                if (c.a >= 0.5) return c; // already painted -> leave unchanged
+
+                float2 ts = _MainTex_TexelSize.xy;
+                float best = 1e20;
+                fixed3 bestCol = c.rgb;
+                bool found = false;
+
+                // Search the neighborhood (up to _Pad texels) for the nearest painted texel.
+                [loop] for (int y = -MAXPAD; y <= MAXPAD; y++)
+                {
+                    if (abs(y) > _Pad) continue;
+                    [loop] for (int x = -MAXPAD; x <= MAXPAD; x++)
+                    {
+                        if (abs(x) > _Pad) continue;
+                        fixed4 s = tex2D(_MainTex, i.uv + float2(x, y) * ts);
+                        if (s.a >= 0.5)
+                        {
+                            float dd = (float)(x * x + y * y);
+                            if (dd < best) { best = dd; bestCol = s.rgb; found = true; }
+                        }
+                    }
+                }
+
+                // Gutter: color of the nearest painted texel, but alpha = 0 (not a source).
+                if (found) return fixed4(bestCol, 0.0);
+                return c; // out of range -> base color unchanged
+            }
+            ENDCG
+        }
+    }
+    Fallback Off
+}

Assets/Shaders/MeshPaintDilate.shader.meta

@@ -0,0 +1,9 @@
+fileFormatVersion: 2
+guid: 387abc652c7ac1c449701bdfcf9d0f8b
+ShaderImporter:
+  externalObjects: {}
+  defaultTextures: []
+  nonModifiableTextures: []
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: