fix(lighting): port ACME lighting constants replacing guessed values

Replace guessed sun direction (0.5, 0.4, 0.6) with ACME's verified
value (0.5, 0.3, -0.3) from GameScene.cs:238. Replace hardcoded
ambient/diffuse (0.25/0.75) with ACME's ambient intensity 0.45 from
LandscapeEditorSettings.cs:108.

Terrain shaders now match ACME Landscape.vert/frag pattern:
- Vertex shader computes Lambert term with xLightDirection uniform
- Fragment shader applies: color * (clamp(lambert, 0, 1) + xAmbient)

Static object shader matches ACME StaticObject.vert:
- LightingFactor = max(dot(N, -L), 0) + ambient
- Removed separate uDiffuseIntensity (ACME doesn't have one)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/InstancedMeshRenderer.cs

@@ -142,12 +142,13 @@ public sealed unsafe class InstancedMeshRenderer : IDisposable
         var vp = camera.View * camera.Projection;
         _shader.SetMatrix4("uViewProjection", vp);
 
-        // Lighting uniforms — match the constants from mesh.frag so the visual
-        // output is identical to the non-instanced path.
-        var sunDir = Vector3.Normalize(new Vector3(0.5f, 0.4f, 0.6f));
-        _shader.SetVec3("uLightDirection", sunDir);
-        _shader.SetFloat("uAmbientIntensity", 0.25f);
-        _shader.SetFloat("uDiffuseIntensity", 0.75f);
+        // Lighting uniforms matching ACME StaticObject.vert:
+        //   LightingFactor = max(dot(Normal, -uLightDirection), 0.0) + uAmbientIntensity
+        // LightDirection (0.5, 0.3, -0.3) from ACME GameScene.cs:238.
+        // AmbientLightIntensity 0.45 from ACME LandscapeEditorSettings.cs:108.
+        var lightDir = Vector3.Normalize(new Vector3(0.5f, 0.3f, -0.3f));
+        _shader.SetVec3("uLightDirection", lightDir);
+        _shader.SetFloat("uAmbientIntensity", 0.45f);
 
         // ── Collect and group instances ───────────────────────────────────────
         CollectGroups(landblockEntries, frustum, neverCullLandblockId);

src/AcDream.App/Rendering/Shaders/mesh_instanced.vert

@@ -16,9 +16,8 @@ layout(location = 5) in vec4 aInstanceRow2;
 layout(location = 6) in vec4 aInstanceRow3;
 
 uniform mat4 uViewProjection;
-uniform vec3 uLightDirection;   // world-space sun direction (points toward sun)
+uniform vec3 uLightDirection;   // world-space light direction (points FROM sun, matching ACME)
 uniform float uAmbientIntensity;
-uniform float uDiffuseIntensity;
 
 out vec2 vTex;
 out vec3 vWorldNormal;
@@ -26,21 +25,16 @@ out float vLightingFactor;
 
 void main() {
     // Reconstruct the per-instance model matrix from its four row vectors.
-    // Column-major storage: OpenGL/GLSL mat4 columns are constructed from
-    // the rows we receive from the attribute buffer.
     mat4 model = mat4(aInstanceRow0, aInstanceRow1, aInstanceRow2, aInstanceRow3);
 
     vec4 worldPos = model * vec4(aPosition, 1.0);
     gl_Position = uViewProjection * worldPos;
 
-    // Transform normal into world space.  For uniform-scale transforms the
-    // upper-left 3x3 is sufficient; non-uniform scale would require the
-    // inverse transpose, accepted as a future-phase concern (same as mesh.vert).
+    // Transform normal into world space.
     vWorldNormal = normalize(mat3(model) * aNormal);
     vTex = aTexCoord;
 
-    // Compute Lambert diffuse + ambient in the vertex shader so the fragment
-    // shader only needs a multiply.  Matches ACME StaticObject.vert pattern.
-    float ndotl = max(dot(vWorldNormal, uLightDirection), 0.0);
-    vLightingFactor = uAmbientIntensity + uDiffuseIntensity * ndotl;
+    // Lambert + ambient matching ACME StaticObject.vert:
+    //   LightingFactor = max(dot(Normal, -uLightDirection), 0.0) + uAmbientIntensity;
+    vLightingFactor = max(dot(vWorldNormal, -uLightDirection), 0.0) + uAmbientIntensity;
 }

src/AcDream.App/Rendering/Shaders/terrain.frag

@@ -6,6 +6,7 @@
 
 in  vec2  vBaseUV;
 in  vec3  vWorldNormal;
+in  float vLightingFactor;
 in  vec4  vOverlay0;
 in  vec4  vOverlay1;
 in  vec4  vOverlay2;
@@ -17,11 +18,7 @@ out vec4 fragColor;
 
 uniform sampler2DArray uTerrain;   // 33+ layers — TerrainAtlas.GlTexture
 uniform sampler2DArray uAlpha;     // 8+  layers — TerrainAtlas.GlAlphaTexture
-
-// Phase 3a lighting (in sync with mesh.frag — update both together).
-const vec3  SUN_DIR = normalize(vec3(0.5, 0.4, 0.6));
-const float AMBIENT = 0.25;
-const float DIFFUSE = 0.75;
+uniform float xAmbient;            // ambient intensity (matching ACME Landscape.frag)
 
 // Per-texture tiling repeat count across a cell. WorldBuilder uses
 // uTexTiling[36] uploaded from the dats; we default to 1.0 (one tile per
@@ -118,10 +115,9 @@ void main() {
     vec3 roadMasked = roads.rgb     *  roads.a;
     vec3 rgb = clamp(baseMasked + ovlMasked + roadMasked, 0.0, 1.0);
 
-    // Phase 3a/3b directional lighting (in sync with mesh.frag constants).
-    vec3 N = normalize(vWorldNormal);
-    float ndotl = max(dot(N, SUN_DIR), 0.0);
-    float lighting = AMBIENT + DIFFUSE * ndotl;
+    // Lighting matching ACME Landscape.frag:
+    //   litColor = finalColor * (saturate(vLightingFactor) + xAmbient);
+    vec3 litColor = rgb * (clamp(vLightingFactor, 0.0, 1.0) + xAmbient);
 
-    fragColor = vec4(rgb * lighting, 1.0);
+    fragColor = vec4(litColor, 1.0);
 }

src/AcDream.App/Rendering/Shaders/terrain.vert

@@ -8,9 +8,11 @@ layout(location = 5) in uvec4 aPacked3;  // bits: rot fields + splitDir (see bel
 
 uniform mat4 uView;
 uniform mat4 uProjection;
+uniform vec3 xLightDirection;   // world-space sun direction (matching ACME Landscape.vert)
 
 out vec2  vBaseUV;
 out vec3  vWorldNormal;
+out float vLightingFactor;
 // Per-layer "UV.xy in cell-local 0..1 space, tex index .z, alpha index .w".
 // Negative .z means "layer not present, skip it in the fragment shader."
 out vec4  vOverlay0;
@@ -91,6 +93,10 @@ void main() {
     // Vertices are baked in world space; normals need no model transform.
     vWorldNormal = normalize(aNormal);
 
+    // Lambert diffuse term matching ACME Landscape.vert:
+    // vLightingFactor = max(0.0, dot(vNormal, -normalize(xLightDirection)));
+    vLightingFactor = max(0.0, dot(vWorldNormal, -normalize(xLightDirection)));
+
     float baseTex = float(aPacked0.x);
     if (baseTex >= 254.0) baseTex = -1.0;
     vBaseTexIdx = baseTex;

src/AcDream.App/Rendering/TerrainChunkRenderer.cs

@@ -218,6 +218,13 @@ public sealed unsafe class TerrainChunkRenderer : IDisposable
         _shader.SetMatrix4("uView", camera.View);
         _shader.SetMatrix4("uProjection", camera.Projection);
 
+        // Lighting uniforms matching ACME Landscape.vert/frag.
+        // LightDirection (0.5, 0.3, -0.3) from ACME GameScene.cs:238.
+        // AmbientLightIntensity 0.45 from ACME LandscapeEditorSettings.cs:108.
+        var lightDir = Vector3.Normalize(new Vector3(0.5f, 0.3f, -0.3f));
+        _shader.SetVec3("xLightDirection", lightDir);
+        _shader.SetFloat("xAmbient", 0.45f);
+
         // Terrain atlas on unit 0, alpha atlas on unit 1.
         _gl.ActiveTexture(TextureUnit.Texture0);
         _gl.BindTexture(TextureTarget.Texture2DArray, _atlas.GlTexture);