[Impeller] Don't place vertex buffer bindings in the Binding map.

impeller/core/buffer_view.h

@@ -15,7 +15,7 @@ struct BufferView {
   uint8_t* contents;
   Range range;
 
-  constexpr operator bool() const { return static_cast<bool>(buffer); }
+  constexpr explicit operator bool() const { return static_cast<bool>(buffer); }
 };
 
 }  // namespace impeller

impeller/renderer/backend/gles/buffer_bindings_gles.cc

@@ -177,12 +177,6 @@ bool BufferBindingsGLES::BindUniformBuffer(const ProcTableGLES& gl,
                                            Allocator& transients_allocator,
                                            const BufferResource& buffer) const {
   const auto* metadata = buffer.GetMetadata();
-  if (metadata == nullptr) {
-    // Vertex buffer bindings don't have metadata as those definitions are
-    // already handled by vertex attrib pointers. Keep going.
-    return true;
-  }
-
   auto device_buffer =
       buffer.resource.buffer->GetDeviceBuffer(transients_allocator);
   if (!device_buffer) {

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -18,6 +18,7 @@
 #include "impeller/renderer/backend/metal/pipeline_mtl.h"
 #include "impeller/renderer/backend/metal/sampler_mtl.h"
 #include "impeller/renderer/backend/metal/texture_mtl.h"
+#include "impeller/renderer/vertex_descriptor.h"
 
 namespace impeller {
 
@@ -407,6 +408,13 @@ static bool Bind(PassBindingsCache& pass,
   auto bind_stage_resources = [&allocator, &pass_bindings](
                                   const Bindings& bindings,
                                   ShaderStage stage) -> bool {
+    if (stage == ShaderStage::kVertex) {
+      if (!Bind(pass_bindings, *allocator, stage,
+                VertexDescriptor::kReservedVertexBufferIndex,
+                bindings.vertex_buffer.view.resource)) {
+        return false;
+      }
+    }
     for (const auto& buffer : bindings.buffers) {
       if (!Bind(pass_bindings, *allocator, stage, buffer.first,
                 buffer.second.view.resource)) {

impeller/renderer/backend/vulkan/render_pass_vk.cc

@@ -382,11 +382,6 @@ static bool AllocateAndBindDescriptorSets(const ContextVK& context,
         return false;
       }
 
-      // Reserved index used for per-vertex data.
-      if (buffer_index == VertexDescriptor::kReservedVertexBufferIndex) {
-        continue;
-      }
-
       if (!encoder.Track(device_buffer)) {
         return false;
       }

impeller/renderer/command.cc

@@ -18,7 +18,7 @@ bool Command::BindVertices(const VertexBuffer& buffer) {
     return false;
   }
 
-  vertex_bindings.buffers[VertexDescriptor::kReservedVertexBufferIndex] =
+  vertex_bindings.vertex_buffer =
       BufferAndUniformSlot{.slot = {}, .view = {nullptr, buffer.vertex_buffer}};
   index_buffer = buffer.index_buffer;
   vertex_count = buffer.vertex_count;
@@ -27,12 +27,7 @@ bool Command::BindVertices(const VertexBuffer& buffer) {
 }
 
 BufferView Command::GetVertexBuffer() const {
-  auto found = vertex_bindings.buffers.find(
-      VertexDescriptor::kReservedVertexBufferIndex);
-  if (found != vertex_bindings.buffers.end()) {
-    return found->second.view.resource;
-  }
-  return {};
+  return vertex_bindings.vertex_buffer.view.resource;
 }
 
 bool Command::BindResource(ShaderStage stage,
@@ -55,6 +50,7 @@ bool Command::DoBindResource(ShaderStage stage,
                              const ShaderUniformSlot& slot,
                              const T metadata,
                              const BufferView& view) {
+  FML_DCHECK(slot.ext_res_0 != VertexDescriptor::kReservedVertexBufferIndex);
   if (!view) {
     return false;
   }

impeller/renderer/command.h

@@ -77,6 +77,8 @@ struct BufferAndUniformSlot {
 struct Bindings {
   std::map<size_t, TextureAndSampler> sampled_images;
   std::map<size_t, BufferAndUniformSlot> buffers;
+  // This is only valid for vertex bindings.
+  BufferAndUniformSlot vertex_buffer;
 };
 
 //------------------------------------------------------------------------------