[Impeller] Add a way to query the gfx backend type.

Author: bdero

impeller/aiks/testing/context_mock.h

@@ -7,6 +7,7 @@
 #include <string>
 #include <vector>
 
+#include "gmock/gmock-function-mocker.h"
 #include "gmock/gmock.h"
 #include "impeller/renderer/command_buffer.h"
 #include "impeller/renderer/context.h"
@@ -64,6 +65,8 @@ class ContextMock : public Context {
  public:
   MOCK_CONST_METHOD0(DescribeGpuModel, std::string());
 
+  MOCK_CONST_METHOD0(GetBackendType, Context::BackendType());
+
   MOCK_CONST_METHOD0(IsValid, bool());
 
   MOCK_CONST_METHOD0(GetCapabilities,

impeller/renderer/backend/gles/context_gles.cc

@@ -86,6 +86,10 @@ ContextGLES::ContextGLES(std::unique_ptr<ProcTableGLES> gl,
 
 ContextGLES::~ContextGLES() = default;
 
+Context::BackendType ContextGLES::GetBackendType() const {
+  return Context::BackendType::kOpenGLES;
+}
+
 const ReactorGLES::Ref& ContextGLES::GetReactor() const {
   return reactor_;
 }

impeller/renderer/backend/gles/context_gles.h

@@ -28,6 +28,9 @@ class ContextGLES final : public Context,
   // |Context|
   ~ContextGLES() override;
 
+  // |Context|
+  BackendType GetBackendType() const override;
+
   const ReactorGLES::Ref& GetReactor() const;
 
   std::optional<ReactorGLES::WorkerID> AddReactorWorker(

impeller/renderer/backend/metal/context_mtl.h

@@ -52,6 +52,9 @@ class ContextMTL final : public Context,
   // |Context|
   ~ContextMTL() override;
 
+  // |Context|
+  BackendType GetBackendType() const override;
+
   id<MTLDevice> GetMTLDevice() const;
 
   // |Context|

impeller/renderer/backend/metal/context_mtl.mm

@@ -286,6 +286,10 @@ new ContextMTL(device, command_queue,
 
 ContextMTL::~ContextMTL() = default;
 
+Context::BackendType ContextMTL::GetBackendType() const {
+  return Context::BackendType::kMetal;
+}
+
 // |Context|
 std::string ContextMTL::DescribeGpuModel() const {
   return std::string([[device_ name] UTF8String]);

impeller/renderer/backend/vulkan/context_vk.cc

@@ -120,6 +120,10 @@ ContextVK::~ContextVK() {
   CommandPoolVK::ClearAllPools(this);
 }
 
+Context::BackendType ContextVK::GetBackendType() const {
+  return Context::BackendType::kVulkan;
+}
+
 void ContextVK::Setup(Settings settings) {
   TRACE_EVENT0("impeller", "ContextVK::Setup");
 

impeller/renderer/backend/vulkan/context_vk.h

@@ -55,6 +55,9 @@ class ContextVK final : public Context,
   // |Context|
   ~ContextVK() override;
 
+  // |Context|
+  BackendType GetBackendType() const override;
+
   // |Context|
   std::string DescribeGpuModel() const override;
 

impeller/renderer/context.h

@@ -43,11 +43,32 @@ class Allocator;
 ///             `//impeller/renderer/backend`.
 class Context {
  public:
+  enum class BackendType {
+    kMetal,
+    kOpenGLES,
+    kVulkan,
+  };
+
   //----------------------------------------------------------------------------
   /// @brief      Destroys an Impeller context.
   ///
   virtual ~Context();
 
+  //----------------------------------------------------------------------------
+  /// @brief      Get the graphics backend of an Impeller context.
+  ///
+  ///             This is useful for cases where a renderer needs to track and
+  ///             lookup backend-specific resources, like shaders or uniform
+  ///             layout information.
+  ///
+  ///             It's not recommended to use this as a substitute for
+  ///             per-backend capability checking. Instead, check for specific
+  ///             capabilities via `GetCapabilities()`.
+  ///
+  /// @return     The graphics backend of the `Context`.
+  ///
+  virtual BackendType GetBackendType() const = 0;
+
   // TODO(129920): Refactor and move to capabilities.
   virtual std::string DescribeGpuModel() const = 0;