Fix uniform alignment on a per platform basis.

engine/src/flutter/impeller/compositor/BUILD.gn

@@ -34,6 +34,8 @@ impeller_component("compositor") {
     "pipeline_descriptor.mm",
     "pipeline_library.h",
     "pipeline_library.mm",
+    "platform.h",
+    "platform.mm",
     "range.cc",
     "range.h",
     "render_pass.h",

engine/src/flutter/impeller/compositor/host_buffer.h

@@ -12,6 +12,7 @@
 #include "flutter/fml/macros.h"
 #include "impeller/compositor/buffer.h"
 #include "impeller/compositor/buffer_view.h"
+#include "impeller/compositor/platform.h"
 
 namespace impeller {
 
@@ -29,6 +30,12 @@ class HostBuffer final : public std::enable_shared_from_this<HostBuffer>,
 
   size_t GetReservedLength() const;
 
+  template <class T, class = std::enable_if_t<std::is_standard_layout_v<T>>>
+  [[nodiscard]] BufferView EmplaceUniform(const T& t) {
+    return Emplace(reinterpret_cast<const void*>(&t), sizeof(T),
+                   std::max(alignof(T), DefaultUniformAlignment()));
+  }
+
   template <class T, class = std::enable_if_t<std::is_standard_layout_v<T>>>
   [[nodiscard]] BufferView Emplace(const T& t) {
     return Emplace(reinterpret_cast<const void*>(&t), sizeof(T), alignof(T));

engine/src/flutter/impeller/compositor/platform.h

@@ -0,0 +1,24 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#pragma once
+
+#include <cstddef>
+
+#include "flutter/fml/build_config.h"
+#include "flutter/fml/macros.h"
+
+namespace impeller {
+
+constexpr size_t DefaultUniformAlignment() {
+#if OS_IOS
+  return 16u;
+#elif OS_MACOSX
+  return 256u;
+#else
+#error "Unsupported platform".
+#endif
+}
+
+}  // namespace impeller

engine/src/flutter/impeller/compositor/platform.mm

@@ -0,0 +1,11 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "impeller/compositor/platform.h"
+
+namespace impeller {
+
+//
+
+}  // namespace impeller

engine/src/flutter/impeller/compositor/render_pass.h

@@ -71,6 +71,8 @@ class RenderPass {
 
   bool IsValid() const;
 
+  void SetLabel(std::string label);
+
   HostBuffer& GetTransientsBuffer();
 
   [[nodiscard]] bool RecordCommand(Command command);
@@ -84,6 +86,7 @@ class RenderPass {
   MTLRenderPassDescriptor* desc_ = nil;
   std::vector<Command> commands_;
   std::shared_ptr<HostBuffer> transients_buffer_;
+  std::string label_;
   bool is_valid_ = false;
 
   RenderPass(id<MTLCommandBuffer> buffer, const RenderPassDescriptor& desc);

engine/src/flutter/impeller/compositor/render_pass.mm

@@ -137,14 +137,24 @@ bool RenderPass::IsValid() const {
   return is_valid_;
 }
 
+void RenderPass::SetLabel(std::string label) {
+  label_ = std::move(label);
+}
+
 bool RenderPass::FinishEncoding(Allocator& transients_allocator) const {
   if (!IsValid()) {
     return false;
   }
   auto pass = [buffer_ renderCommandEncoderWithDescriptor:desc_];
+
   if (!pass) {
     return false;
   }
+
+  if (!label_.empty()) {
+    [pass setLabel:@(label_.c_str())];
+  }
+
   // Success or failure, the pass must end. The buffer can only process one pass
   // at a time.
   fml::ScopedCleanupClosure auto_end([pass]() { [pass endEncoding]; });

engine/src/flutter/impeller/entity/entity_renderer.mm

@@ -36,6 +36,8 @@ bool EntityRenderer::OnIsValid() const {
 }
 
 bool EntityRenderer::OnRender(RenderPass& pass) {
+  pass.SetLabel("EntityRenderer");
+
   shader::BoxVertexInfo::UniformBuffer uniforms;
   uniforms.mvp = Matrix::MakeOrthographic({800, 600});
   VertexBufferBuilder vertices;
@@ -47,14 +49,14 @@ bool EntityRenderer::OnRender(RenderPass& pass) {
   });
 
   Command cmd;
-  cmd.label = "Simple Box";
+  cmd.label = "Box";
   cmd.pipeline = box_primitive_->GetPipeline();
-  cmd.vertex_bindings
-      .buffers[shader::BoxVertexInfo::kUniformUniformBuffer.location] =
-      pass.GetTransientsBuffer().Emplace(uniforms);
   cmd.vertex_bindings
       .buffers[shader::BoxVertexInfo::kInputVertexPosition.location] =
       vertices.CreateVertexBuffer(pass.GetTransientsBuffer());
+  cmd.vertex_bindings
+      .buffers[shader::BoxVertexInfo::kUniformUniformBuffer.location] =
+      pass.GetTransientsBuffer().EmplaceUniform(uniforms);
   cmd.index_buffer = vertices.CreateIndexBuffer(pass.GetTransientsBuffer());
   cmd.index_count = vertices.GetIndexCount();
   if (!pass.RecordCommand(std::move(cmd))) {