Reduce duplicate GPU buffer uploads (#3577)

Co-authored-by: “Malcolm <“mtoon@atlasprogramming.com”>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/mbgl/mtl/render_pass.hpp

@@ -41,6 +41,9 @@ public:
     /// Set the sampler for a texture binding
     void setFragmentSamplerState(const MTLSamplerStatePtr&, int32_t location);
 
+    /// Set the render pipeline state
+    void setRenderPipelineState(const MTLRenderPipelineStatePtr&);
+
     void endEncoding();
 
     /// Resets the states and bindings of the render pass to deal
@@ -69,6 +72,8 @@ private:
     mtl::CommandEncoder& commandEncoder;
     MTLRenderCommandEncoderPtr encoder;
     MTLDepthStencilStatePtr currentDepthStencilState;
+    MTLRenderPipelineStatePtr currentPipelineState;
+
     int32_t currentStencilReferenceValue = 0;
     std::vector<gfx::DebugGroup<gfx::RenderPass>> debugGroups;
 

src/mbgl/mtl/buffer_resource.cpp

@@ -103,15 +103,22 @@ void BufferResource::update(const void* newData, std::size_t updateSize, std::si
         // Until we can be sure that the buffer is not still in use to render the
         // previous frame, replace it with a new buffer instead of updating it.
 
-        auto& device = context.getBackend().getDevice();
         const uint8_t* newBufferSource = nullptr;
         std::unique_ptr<uint8_t[]> tempBuffer;
+        const bool updateIsEntireBuffer = (offset == 0 && updateSize == size);
 
+        // If the entire buffer is being updated, make sure it's changed
+        if (updateIsEntireBuffer) {
+            if (memcmp(buffer->contents(), newData, updateSize) == 0) {
+                return;
+            }
+        }
+
+        auto& device = context.getBackend().getDevice();
         // `[MTLBuffer contents]` may involve memory mapping and/or synchronization.  If the entire
         // buffer is being replaced, avoid accessing the old one by creating the new buffer directly
         // from the given data. If it's just being updated, apply the update to a local buffer to
         // avoid needing to access the new buffer.
-        const bool updateIsEntireBuffer = (offset == 0 && updateSize == size);
         if (updateIsEntireBuffer) {
             newBufferSource = static_cast<const uint8_t*>(newData);
         } else {

src/mbgl/mtl/drawable.cpp

@@ -223,7 +223,7 @@ void Drawable::draw(PaintParameters& parameters) const {
             mbgl::util::hash(getColorMode().hash(), impl->vertexDescHash));
     }
     if (impl->pipelineState) {
-        encoder->setRenderPipelineState(impl->pipelineState.get());
+        renderPass.setRenderPipelineState(impl->pipelineState);
     } else {
         assert(!"Failed to create render pipeline state");
         return;

src/mbgl/mtl/render_pass.cpp

@@ -66,6 +66,7 @@ void RenderPass::endEncoding() {
 }
 
 void RenderPass::resetState() {
+    currentPipelineState.reset();
     currentDepthStencilState.reset();
     currentStencilReferenceValue = 0;
     for (int i = 0; i < maxBinds; ++i) {
@@ -193,6 +194,14 @@ void RenderPass::setFragmentSamplerState(const MTLSamplerStatePtr& state, int32_
     }
 }
 
+/// Set the render pipeline state
+void RenderPass::setRenderPipelineState(const MTLRenderPipelineStatePtr& pipelineState) {
+    if (pipelineState != currentPipelineState) {
+        currentPipelineState = pipelineState;
+        encoder->setRenderPipelineState(currentPipelineState.get());
+    }
+}
+
 void RenderPass::setCullMode(const MTL::CullMode mode) {
     if (mode != currentCullMode) {
         encoder->setCullMode(mode);