Material improvements.

Allow multiply-nested MixMaterials in the GPU path.
Switch to Repeat texture mode for bump maps (Amazon bistro expects this).

src/pbrt/gpu/optix.cu

@@ -189,9 +189,10 @@ static __forceinline__ __device__ void ProcessClosestIntersection(
     MaterialHandle material = intr.material;
 
     const MixMaterial *mix = material.CastOrNullptr<MixMaterial>();
-    if (mix) {
-        MaterialEvalContext ctx(intr);
-        material = mix->ChooseMaterial(BasicTextureEvaluator(), ctx);
+    while (mix) {
+         MaterialEvalContext ctx(intr);
+         material = mix->ChooseMaterial(BasicTextureEvaluator(), ctx);
+         mix = material.CastOrNullptr<MixMaterial>();
     }
 
     if (!material) {

src/pbrt/materials.cpp

@@ -108,12 +108,7 @@ MixMaterial *MixMaterial::Create(MaterialHandle materials[2],
         // Check for this stuff here, where we can include the FileLoc in
         // the error message. Note that both of these limitations could be
         // relaxed if they were problematic; the issue is that we currently
-        // resolve MixMaterials in the closest hit shader, where we'd like
-        // to, for example, not introduce the complexity of potentially
-        // recursively evaluating textures, etc.
-        if (materials[0].Is<MixMaterial>() || materials[1].Is<MixMaterial>())
-            ErrorExit(loc, "The GPU renderer doesn't currently support using "
-                           "\"mix\" materials as parameters to the \"mix\" material.");
+        // resolve MixMaterials in the closest hit shader...
         if (!BasicTextureEvaluator().CanEvaluate({amount}, {}))
             ErrorExit(loc, "The GPU renderer currently only supports basic textures "
                            "for its \"amount\" parameter.");

src/pbrt/materials.h

@@ -117,10 +117,11 @@ PBRT_CPU_GPU void Bump(TextureEvaluator texEval, FloatTextureHandle displacement
 
     } else {
         // Sample normal map to compute shading normal
+        WrapMode2D wrap(WrapMode::Repeat);
         Point2f uv(ctx.uv[0], 1 - ctx.uv[1]);
-        Vector3f ns(2 * normalMap->BilerpChannel(uv, 0) - 1,
-                    2 * normalMap->BilerpChannel(uv, 1) - 1,
-                    2 * normalMap->BilerpChannel(uv, 2) - 1);
+        Vector3f ns(2 * normalMap->BilerpChannel(uv, 0, wrap) - 1,
+                    2 * normalMap->BilerpChannel(uv, 1, wrap) - 1,
+                    2 * normalMap->BilerpChannel(uv, 2, wrap) - 1);
         ns = Normalize(ns);
         Frame frame = Frame::FromZ(ctx.shading.n);
         ns = frame.FromLocal(ns);
@@ -345,7 +346,7 @@ class MixMaterial {
         if (amt >= 1)
             return materials[1];
 
-        Float u = uint32_t(Hash(ctx.p, ctx.wo)) * 0x1p-32;
+        Float u = uint32_t(Hash(ctx.p, ctx.wo, materials[0], materials[1])) * 0x1p-32;
         return (amt < u) ? materials[0] : materials[1];
     }