Fix, allow missing bone indices vertex attribute in Metal driver (#1663)

google · Sep 18, 2019 · 5d725f6 · 5d725f6
1 parent 020e9e5
commit 5d725f6
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Showing 2 changed files with 12 additions and 4 deletions.
diff --git a/filament/backend/src/metal/MetalDriver.mm b/filament/backend/src/metal/MetalDriver.mm
@@ -935,9 +935,9 @@
                                           withRange:bufferRange];
 
     // Bind the zero buffer, used for missing vertex attributes.
-    static const char bytes[4] = { 0 };
+    static const char bytes[16] = { 0 };
     [mContext->currentCommandEncoder setVertexBytes:bytes
-                                             length:4
+                                             length:16
                                             atIndex:(VERTEX_BUFFER_START + ZERO_VERTEX_BUFFER)];
 
     MetalIndexBuffer* indexBuffer = primitive->indexBuffer;

diff --git a/filament/backend/src/metal/MetalHandles.mm b/filament/backend/src/metal/MetalHandles.mm
@@ -198,16 +198,24 @@ static inline MTLStorageMode getMetalStorageMode(TextureUsage usage) {
     uint32_t bufferIndex = 0;
     for (uint32_t attributeIndex = 0; attributeIndex < attributeCount; attributeIndex++) {
         if (!(enabledAttributes & (1U << attributeIndex))) {
+            // TODO: all vertex attributes are vec4 (vector of floats), except for
+            // mesh_bone_indices, which is a uvec4 (vector of unsigned integers).
+            // We must use the correct format, but ideally the Metal driver should not need to know
+            // this.
+            const auto boneIndicesLocation = 5; // VertexAttribute::BONE_INDICES
+            const MTLVertexFormat format = attributeIndex == boneIndicesLocation ?
+                    MTLVertexFormatUInt4 : MTLVertexFormatFloat4;
+
             // If the attribute is not enabled, bind it to the zero buffer. It's a Metal error for a
             // shader to read from missing vertex attributes.
             vertexDescription.attributes[attributeIndex] = {
-                    .format = MTLVertexFormatChar4,
+                    .format = format,
                     .buffer = ZERO_VERTEX_BUFFER,
                     .offset = 0
             };
             vertexDescription.layouts[ZERO_VERTEX_BUFFER] = {
                     .step = MTLVertexStepFunctionConstant,
-                    .stride = 4
+                    .stride = 16
             };
             continue;
         }