Split MakeVertexDesc so it is const

Fixed: dawn:1384
Change-Id: I6071097e8d78b8462459623443b66f3afa42d9d8
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/130480
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Brandon Jones <toji@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/dawn/native/metal/PipelineLayoutMTL.h

@@ -47,7 +47,7 @@ class PipelineLayout final : public PipelineLayoutBase {
     const BindingIndexInfo& GetBindingIndexInfo(SingleShaderStage stage) const;
 
     // The number of Metal vertex stage buffers used for the whole pipeline layout.
-    uint32_t GetBufferBindingCount(SingleShaderStage stage);
+    uint32_t GetBufferBindingCount(SingleShaderStage stage) const;
 
   private:
     PipelineLayout(Device* device, const PipelineLayoutDescriptor* descriptor);

src/dawn/native/metal/PipelineLayoutMTL.mm

@@ -77,7 +77,7 @@ const PipelineLayout::BindingIndexInfo& PipelineLayout::GetBindingIndexInfo(
     return mIndexInfo[stage];
 }
 
-uint32_t PipelineLayout::GetBufferBindingCount(SingleShaderStage stage) {
+uint32_t PipelineLayout::GetBufferBindingCount(SingleShaderStage stage) const {
     return mBufferBindingCount[stage];
 }
 

src/dawn/native/metal/RenderPipelineMTL.h

@@ -55,7 +55,7 @@ class RenderPipeline final : public RenderPipelineBase {
   private:
     using RenderPipelineBase::RenderPipelineBase;
 
-    NSRef<MTLVertexDescriptor> MakeVertexDesc();
+    NSRef<MTLVertexDescriptor> MakeVertexDesc() const;
 
     MTLPrimitiveType mMtlPrimitiveTopology;
     MTLWinding mMtlFrontFace;

src/dawn/native/metal/RenderPipelineMTL.mm

@@ -323,19 +323,29 @@ MaybeError RenderPipeline::Initialize() {
     mMtlPrimitiveTopology = MTLPrimitiveTopology(GetPrimitiveTopology());
     mMtlFrontFace = MTLFrontFace(GetFrontFace());
     mMtlCullMode = ToMTLCullMode(GetCullMode());
+    // Build a mapping of vertex buffer slots to packed indices
+    {
+        // Vertex buffers are placed after all the buffers for the bind groups.
+        uint32_t mtlVertexBufferIndex =
+            ToBackend(GetLayout())->GetBufferBindingCount(SingleShaderStage::Vertex);
+
+        for (VertexBufferSlot slot : IterateBitSet(GetVertexBufferSlotsUsed())) {
+            mMtlVertexBufferIndices[slot] = mtlVertexBufferIndex;
+            mtlVertexBufferIndex++;
+        }
+    }
+
     auto mtlDevice = ToBackend(GetDevice())->GetMTLDevice();
 
     NSRef<MTLRenderPipelineDescriptor> descriptorMTLRef =
         AcquireNSRef([MTLRenderPipelineDescriptor new]);
     MTLRenderPipelineDescriptor* descriptorMTL = descriptorMTLRef.Get();
 
-    // TODO(dawn:1384): MakeVertexDesc should be const in the future, so we don't need to call
+    NSRef<MTLVertexDescriptor> vertexDesc;
-    // it here when vertex pulling is enabled
-    NSRef<MTLVertexDescriptor> vertexDesc = MakeVertexDesc();
-
-    // Calling MakeVertexDesc first is important since it sets indices for packed bindings
     if (GetDevice()->IsToggleEnabled(Toggle::MetalEnableVertexPulling)) {
         vertexDesc = AcquireNSRef([MTLVertexDescriptor new]);
+    } else {
+        vertexDesc = MakeVertexDesc();
     }
     descriptorMTL.vertexDescriptor = vertexDesc.Get();
 
@@ -449,13 +459,9 @@ wgpu::ShaderStage RenderPipeline::GetStagesRequiringStorageBufferLength() const
     return mStagesRequiringStorageBufferLength;
 }
 
-NSRef<MTLVertexDescriptor> RenderPipeline::MakeVertexDesc() {
+NSRef<MTLVertexDescriptor> RenderPipeline::MakeVertexDesc() const {
     MTLVertexDescriptor* mtlVertexDescriptor = [MTLVertexDescriptor new];
 
-    // Vertex buffers are packed after all the buffers for the bind groups.
-    uint32_t mtlVertexBufferIndex =
-        ToBackend(GetLayout())->GetBufferBindingCount(SingleShaderStage::Vertex);
-
     for (VertexBufferSlot slot : IterateBitSet(GetVertexBufferSlotsUsed())) {
         const VertexBufferInfo& info = GetVertexBuffer(slot);
 
@@ -486,11 +492,8 @@ NSRef<MTLVertexDescriptor> RenderPipeline::MakeVertexDesc() {
             layoutDesc.stride = info.arrayStride;
         }
 
-        mtlVertexDescriptor.layouts[mtlVertexBufferIndex] = layoutDesc;
+        mtlVertexDescriptor.layouts[GetMtlVertexBufferIndex(slot)] = layoutDesc;
         [layoutDesc release];
-
-        mMtlVertexBufferIndices[slot] = mtlVertexBufferIndex;
-        mtlVertexBufferIndex++;
     }
 
     for (VertexAttributeLocation loc : IterateBitSet(GetAttributeLocationsUsed())) {
@@ -499,7 +502,7 @@ NSRef<MTLVertexDescriptor> RenderPipeline::MakeVertexDesc() {
         auto attribDesc = [MTLVertexAttributeDescriptor new];
         attribDesc.format = VertexFormatType(info.format);
         attribDesc.offset = info.offset;
-        attribDesc.bufferIndex = mMtlVertexBufferIndices[info.vertexBufferSlot];
+        attribDesc.bufferIndex = GetMtlVertexBufferIndex(info.vertexBufferSlot);
         mtlVertexDescriptor.attributes[static_cast<uint8_t>(loc)] = attribDesc;
         [attribDesc release];
     }