[Flutter GPU] Remove Command/VertexBuffer usage from Flutter GPU. (#55893)

Resolves flutter/flutter#156764.
Resolves flutter/flutter#155335.

- Remove Command/VertexBuffer from Flutter GPU.
- Separate vertex/index count into `impeller::RenderPass::SetElementCount(size_t count)` & accurately document its behavior.
- Make Flutter GPU uniform/texture bindings re-assignable.
- Remove unnecessary templates.

Author: bdero

impeller/entity/contents/text_contents.cc

@@ -256,8 +256,9 @@ bool TextContents::Render(const ContentContext& renderer,
         }
       });
 
-  pass.SetVertexBuffer(std::move(buffer_view), vertex_count);
+  pass.SetVertexBuffer(std::move(buffer_view));
   pass.SetIndexBuffer({}, IndexType::kNone);
+  pass.SetElementCount(vertex_count);
 
   return pass.Draw().ok();
 }

impeller/renderer/backend/gles/buffer_bindings_gles.cc

@@ -415,7 +415,7 @@ std::optional<size_t> BufferBindingsGLES::BindTextures(
     /// If there is a sampler for the texture at the same index, configure the
     /// bound texture using that sampler.
     ///
-    const auto& sampler_gles = SamplerGLES::Cast(*data.sampler);
+    const auto& sampler_gles = SamplerGLES::Cast(**data.sampler);
     if (!sampler_gles.ConfigureBoundTexture(texture_gles, gl)) {
       return std::nullopt;
     }

impeller/renderer/backend/gles/render_pass_gles.cc

@@ -455,7 +455,7 @@ static bool BindVertexBuffer(const ProcTableGLES& gl,
     /// Finally! Invoke the draw call.
     ///
     if (command.index_type == IndexType::kNone) {
-      gl.DrawArrays(mode, command.base_vertex, command.vertex_count);
+      gl.DrawArrays(mode, command.base_vertex, command.element_count);
     } else {
       // Bind the index buffer if necessary.
       auto index_buffer_view = command.index_buffer;
@@ -466,7 +466,7 @@ static bool BindVertexBuffer(const ProcTableGLES& gl,
         return false;
       }
       gl.DrawElements(mode,                             // mode
-                      command.vertex_count,             // count
+                      command.element_count,            // count
                       ToIndexType(command.index_type),  // type
                       reinterpret_cast<const GLvoid*>(static_cast<GLsizei>(
                           index_buffer_view.range.offset))  // indices

impeller/renderer/backend/metal/render_pass_mtl.h

@@ -79,13 +79,15 @@ class RenderPassMTL final : public RenderPass {
   // |RenderPass|
   void SetScissor(IRect scissor) override;
 
+  // |RenderPass|
+  void SetElementCount(size_t count) override;
+
   // |RenderPass|
   void SetInstanceCount(size_t count) override;
 
   // |RenderPass|
   bool SetVertexBuffer(BufferView vertex_buffers[],
-                       size_t vertex_buffer_count,
-                       size_t vertex_count) override;
+                       size_t vertex_buffer_count) override;
 
   // |RenderPass|
   bool SetIndexBuffer(BufferView index_buffer, IndexType index_type) override;

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -283,15 +283,19 @@ static bool Bind(PassBindingsCacheMTL& pass,
   pass_bindings_.SetScissor(scissor);
 }
 
+// |RenderPass|
+void RenderPassMTL::SetElementCount(size_t count) {
+  vertex_count_ = count;
+}
+
 // |RenderPass|
 void RenderPassMTL::SetInstanceCount(size_t count) {
   instance_count_ = count;
 }
 
 // |RenderPass|
 bool RenderPassMTL::SetVertexBuffer(BufferView vertex_buffers[],
-                                    size_t vertex_buffer_count,
-                                    size_t vertex_count) {
+                                    size_t vertex_buffer_count) {
   if (!ValidateVertexBuffers(vertex_buffers, vertex_buffer_count)) {
     return false;
   }
@@ -304,8 +308,6 @@ static bool Bind(PassBindingsCacheMTL& pass,
     }
   }
 
-  vertex_count_ = vertex_count;
-
   return true;
 }
 

impeller/renderer/backend/vulkan/render_pass_vk.cc

@@ -364,15 +364,19 @@ void RenderPassVK::SetScissor(IRect scissor) {
   command_buffer_vk_.setScissor(0, 1, &scissor_vk);
 }
 
+// |RenderPass|
+void RenderPassVK::SetElementCount(size_t count) {
+  element_count_ = count;
+}
+
 // |RenderPass|
 void RenderPassVK::SetInstanceCount(size_t count) {
   instance_count_ = count;
 }
 
 // |RenderPass|
 bool RenderPassVK::SetVertexBuffer(BufferView vertex_buffers[],
-                                   size_t vertex_buffer_count,
-                                   size_t vertex_count) {
+                                   size_t vertex_buffer_count) {
   if (!ValidateVertexBuffers(vertex_buffers, vertex_buffer_count)) {
     return false;
   }
@@ -389,8 +393,6 @@ bool RenderPassVK::SetVertexBuffer(BufferView vertex_buffers[],
   command_buffer_vk_.bindVertexBuffers(0u, vertex_buffer_count, buffers,
                                        vertex_buffer_offsets);
 
-  vertex_count_ = vertex_count;
-
   return true;
 }
 
@@ -506,14 +508,14 @@ fml::Status RenderPassVK::Draw() {
   }
 
   if (has_index_buffer_) {
-    command_buffer_vk_.drawIndexed(vertex_count_,    // index count
+    command_buffer_vk_.drawIndexed(element_count_,   // index count
                                    instance_count_,  // instance count
                                    0u,               // first index
                                    base_vertex_,     // vertex offset
                                    0u                // first instance
     );
   } else {
-    command_buffer_vk_.draw(vertex_count_,    // vertex count
+    command_buffer_vk_.draw(element_count_,   // vertex count
                             instance_count_,  // instance count
                             base_vertex_,     // vertex offset
                             0u                // first instance
@@ -532,7 +534,7 @@ fml::Status RenderPassVK::Draw() {
   descriptor_write_offset_ = 0u;
   instance_count_ = 1u;
   base_vertex_ = 0u;
-  vertex_count_ = 0u;
+  element_count_ = 0u;
   pipeline_ = nullptr;
   pipeline_uses_input_attachments_ = false;
   immutable_sampler_ = nullptr;

impeller/renderer/backend/vulkan/render_pass_vk.h

@@ -46,7 +46,7 @@ class RenderPassVK final : public RenderPass {
   size_t descriptor_write_offset_ = 0u;
   size_t instance_count_ = 1u;
   size_t base_vertex_ = 0u;
-  size_t vertex_count_ = 0u;
+  size_t element_count_ = 0u;
   bool has_index_buffer_ = false;
   bool has_label_ = false;
   const Pipeline<PipelineDescriptor>* pipeline_;
@@ -76,13 +76,15 @@ class RenderPassVK final : public RenderPass {
   // |RenderPass|
   void SetScissor(IRect scissor) override;
 
+  // |RenderPass|
+  void SetElementCount(size_t count) override;
+
   // |RenderPass|
   void SetInstanceCount(size_t count) override;
 
   // |RenderPass|
   bool SetVertexBuffer(BufferView vertex_buffers[],
-                       size_t vertex_buffer_count,
-                       size_t vertex_count) override;
+                       size_t vertex_buffer_count) override;
 
   // |RenderPass|
   bool SetIndexBuffer(BufferView index_buffer, IndexType index_type) override;

impeller/renderer/command.cc

@@ -20,7 +20,7 @@ bool Command::BindVertices(const VertexBuffer& buffer) {
 
   vertex_buffers = {buffer.vertex_buffer};
   vertex_buffer_count = 1u;
-  vertex_count = buffer.vertex_count;
+  element_count = buffer.vertex_count;
   index_buffer = buffer.index_buffer;
   index_type = buffer.index_type;
   return true;
@@ -89,14 +89,14 @@ bool Command::BindResource(ShaderStage stage,
       vertex_bindings.sampled_images.emplace_back(TextureAndSampler{
           .slot = slot,
           .texture = {&metadata, std::move(texture)},
-          .sampler = sampler,
+          .sampler = &sampler,
       });
       return true;
     case ShaderStage::kFragment:
       fragment_bindings.sampled_images.emplace_back(TextureAndSampler{
           .slot = slot,
           .texture = {&metadata, std::move(texture)},
-          .sampler = sampler,
+          .sampler = &sampler,
       });
       return true;
     case ShaderStage::kCompute:

impeller/renderer/command.h

@@ -61,7 +61,7 @@ using TextureResource = Resource<std::shared_ptr<const Texture>>;
 struct TextureAndSampler {
   SampledImageSlot slot;
   TextureResource texture;
-  const std::unique_ptr<const Sampler>& sampler;
+  const std::unique_ptr<const Sampler>* sampler;
 };
 
 /// @brief combines the buffer resource and its uniform slot information.
@@ -160,14 +160,13 @@ struct Command : public ResourceBinder {
   BufferView index_buffer;
 
   //----------------------------------------------------------------------------
-  /// The total count of vertices, either in the vertex_buffer if the
-  /// index_type is IndexType::kNone or in the index_buffer otherwise.
-  size_t vertex_count = 0u;
+  /// The number of elements to draw. When only a vertex buffer is set, this is
+  /// the vertex count. When an index buffer is set, this is the index count.
+  size_t element_count = 0u;
 
   //----------------------------------------------------------------------------
   /// The type of indices in the index buffer. The indices must be tightly
   /// packed in the index buffer.
-  ///
   IndexType index_type = IndexType::kUnknown;
 
   //----------------------------------------------------------------------------

impeller/renderer/render_pass.cc

@@ -72,7 +72,7 @@ bool RenderPass::AddCommand(Command&& command) {
     }
   }
 
-  if (command.vertex_count == 0u || command.instance_count == 0u) {
+  if (command.element_count == 0u || command.instance_count == 0u) {
     // Essentially a no-op. Don't record the command but this is not necessary
     // an error either.
     return true;
@@ -117,40 +117,40 @@ void RenderPass::SetScissor(IRect scissor) {
   pending_.scissor = scissor;
 }
 
+void RenderPass::SetElementCount(size_t count) {
+  pending_.element_count = count;
+}
+
 void RenderPass::SetInstanceCount(size_t count) {
   pending_.instance_count = count;
 }
 
 bool RenderPass::SetVertexBuffer(VertexBuffer buffer) {
-  if (!SetVertexBuffer(&buffer.vertex_buffer, 1u, buffer.vertex_count)) {
+  if (!SetVertexBuffer(&buffer.vertex_buffer, 1u)) {
     return false;
   }
   if (!SetIndexBuffer(buffer.index_buffer, buffer.index_type)) {
     return false;
   }
+  SetElementCount(buffer.vertex_count);
 
   return true;
 }
 
-bool RenderPass::SetVertexBuffer(BufferView vertex_buffer,
-                                 size_t vertex_count) {
-  return SetVertexBuffer(&vertex_buffer, 1, vertex_count);
+bool RenderPass::SetVertexBuffer(BufferView vertex_buffer) {
+  return SetVertexBuffer(&vertex_buffer, 1);
 }
 
-bool RenderPass::SetVertexBuffer(std::vector<BufferView> vertex_buffers,
-                                 size_t vertex_count) {
-  return SetVertexBuffer(vertex_buffers.data(), vertex_buffers.size(),
-                         vertex_count);
+bool RenderPass::SetVertexBuffer(std::vector<BufferView> vertex_buffers) {
+  return SetVertexBuffer(vertex_buffers.data(), vertex_buffers.size());
 }
 
 bool RenderPass::SetVertexBuffer(BufferView vertex_buffers[],
-                                 size_t vertex_buffer_count,
-                                 size_t vertex_count) {
+                                 size_t vertex_buffer_count) {
   if (!ValidateVertexBuffers(vertex_buffers, vertex_buffer_count)) {
     return false;
   }
 
-  pending_.vertex_count = vertex_count;
   pending_.vertex_buffer_count = vertex_buffer_count;
   for (size_t i = 0; i < vertex_buffer_count; i++) {
     pending_.vertex_buffers[i] = std::move(vertex_buffers[i]);