Revert of Fix assorted issues with remote CoreAnimation (patchset #2 of...

Revert of Fix assorted issues with remote CoreAnimation (patchset #2 of https://codereview.chromium.org/516643002/)

Reason for revert:
Speculatively reverting to see if this helps the mac perf bots:
https://code.google.com/p/chromium/issues/detail?id=408673

Original issue's description:
> Fix assorted issues with remote CoreAnimation
>
> These issues came up while running for a few days with the
> flag --enable-remote-core-animation.
>
> Fix flashes of old frames by hooking up the DiscardBackbuffer (which
> happens when being made non-visible) to re-set the CAContext and
> CALayer (so the browser gets a new one with new content for the next
> frame).
>
> Add support for disabling vsync by using setNeedsDisplay to draw.
>
> Change the backpressure mechanism to rely on the browser to apply
> backpressure in its compositor via the cc:: output surface.
>
> Add a ScopedSetGLToRealGLApi structure to ensure that we are talking
> to the real GL API while in the CoreAnimation callback.
>
> BUG=312462
>
> Committed: https://chromium.googlesource.com/chromium/src/+/3b6aee8ed0393d852ed21fae78f539ffffe3e8f8

TBR=piman@chromium.org,ccameron@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=312462

Review URL: https://codereview.chromium.org/517733002

Cr-Commit-Position: refs/heads/master@{#292438}

content/browser/compositor/browser_compositor_view_private_mac.mm

@@ -61,7 +61,6 @@ BrowserCompositorViewMacInternal::BrowserCompositorViewMacInternal()
       native_widget_,
       content::GetContextFactory(),
       RenderWidgetResizeHelper::Get()->task_runner()));
-  compositor_->SetVisible(false);
 }
 
 BrowserCompositorViewMacInternal::~BrowserCompositorViewMacInternal() {
@@ -82,7 +81,6 @@ void BrowserCompositorViewMacInternal::SetClient(
   DCHECK(background_layer);
   [flipped_layer_ setBounds:[background_layer bounds]];
   [background_layer addSublayer:flipped_layer_];
-  compositor_->SetVisible(true);
 }
 
 void BrowserCompositorViewMacInternal::ResetClient() {
@@ -100,7 +98,6 @@ void BrowserCompositorViewMacInternal::ResetClient() {
   accelerated_output_surface_id_ = 0;
   last_swap_size_dip_ = gfx::Size();
 
-  compositor_->SetVisible(false);
   compositor_->SetScaleAndSize(1.0, gfx::Size(0, 0));
   compositor_->SetRootLayer(NULL);
   client_ = NULL;

content/common/gpu/image_transport_surface_calayer_mac.h

@@ -28,27 +28,18 @@ class CALayerStorageProvider
       CGLContextObj context, GLuint texture,
       gfx::Size pixel_size, float scale_factor) OVERRIDE;
   virtual void FreeColorBufferStorage() OVERRIDE;
-  virtual void SwapBuffers(const gfx::Size& size, float scale_factor) OVERRIDE;
-  virtual void WillWriteToBackbuffer() OVERRIDE;
-  virtual void DiscardBackbuffer() OVERRIDE;
-  virtual void SwapBuffersAckedByBrowser() OVERRIDE;
+  virtual uint64 GetSurfaceHandle() const OVERRIDE;
+  virtual void WillSwapBuffers() OVERRIDE;
+  virtual void CanFreeSwappedBuffer() OVERRIDE;
 
   // Interface to ImageTransportLayer:
   CGLContextObj LayerShareGroupContext();
   bool LayerCanDraw();
   void LayerDoDraw();
-  void LayerResetStorageProvider();
 
  private:
-  void DrawWithVsyncDisabled();
-  void SendPendingSwapToBrowserAfterFrameDrawn();
-
   ImageTransportSurfaceFBO* transport_surface_;
 
-  // Used to determine if we should use setNeedsDisplay or setAsynchronous to
-  // animate.
-  const bool gpu_vsync_disabled_;
-
   // Set when a new swap occurs, and un-set when |layer_| draws that frame.
   bool has_pending_draw_;
 
@@ -62,13 +53,11 @@ class CALayerStorageProvider
   base::ScopedTypeRef<CGLContextObj> share_group_context_;
   GLuint fbo_texture_;
   gfx::Size fbo_pixel_size_;
-  float fbo_scale_factor_;
 
   // The CALayer that the current frame is being drawn into.
   base::scoped_nsobject<CAContext> context_;
   base::scoped_nsobject<ImageTransportLayer> layer_;
 
-  base::WeakPtrFactory<CALayerStorageProvider> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(CALayerStorageProvider);
 };
 

content/common/gpu/image_transport_surface_calayer_mac.mm

@@ -4,13 +4,10 @@
 
 #include "content/common/gpu/image_transport_surface_calayer_mac.h"
 
-#include "base/command_line.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "content/common/gpu/surface_handle_types_mac.h"
 #include "ui/base/cocoa/animation_utils.h"
 #include "ui/gfx/geometry/size_conversions.h"
-#include "ui/gl/gl_gl_api_implementation.h"
-#include "ui/gl/gl_switches.h"
 
 @interface ImageTransportLayer : CAOpenGLLayer {
   content::CALayerStorageProvider* storageProvider_;
@@ -29,8 +26,6 @@
 }
 
 - (void)resetStorageProvider {
-  if (storageProvider_)
-    storageProvider_->LayerResetStorageProvider();
   storageProvider_ = NULL;
 }
 
@@ -65,10 +60,6 @@
              pixelFormat:(CGLPixelFormatObj)pixelFormat
             forLayerTime:(CFTimeInterval)timeInterval
              displayTime:(const CVTimeStamp*)timeStamp {
-  // While in this callback, CoreAnimation has set |glContext| to be current.
-  // Ensure that the GL calls that we make are made against the native GL API.
-  gfx::ScopedSetGLToRealGLApi scoped_set_gl_api;
-
   if (storageProvider_) {
     storageProvider_->LayerDoDraw();
   } else {
@@ -88,13 +79,17 @@ namespace content {
 CALayerStorageProvider::CALayerStorageProvider(
     ImageTransportSurfaceFBO* transport_surface)
         : transport_surface_(transport_surface),
-          gpu_vsync_disabled_(CommandLine::ForCurrentProcess()->HasSwitch(
-              switches::kDisableGpuVsync)),
           has_pending_draw_(false),
           can_draw_returned_false_count_(0),
-          fbo_texture_(0),
-          fbo_scale_factor_(1),
-          weak_factory_(this) {}
+          fbo_texture_(0) {
+  // Allocate a CAContext to use to transport the CALayer to the browser
+  // process.
+  base::scoped_nsobject<NSDictionary> dict([[NSDictionary alloc] init]);
+  CGSConnectionID connection_id = CGSMainConnectionID();
+  context_.reset([CAContext contextWithCGSConnection:connection_id
+                                             options:dict]);
+  [context_ retain];
+}
 
 CALayerStorageProvider::~CALayerStorageProvider() {
 }
@@ -131,12 +126,15 @@ bool CALayerStorageProvider::AllocateColorBufferStorage(
   // Disable the fade-in animation as the layer is changed.
   ScopedCAActionDisabler disabler;
 
-  // Set the parameters that will be used to allocate the CALayer to draw the
-  // texture into.
+  // Allocate a CALayer to draw texture into.
   share_group_context_.reset(CGLRetainContext(context));
   fbo_texture_ = texture;
   fbo_pixel_size_ = pixel_size;
-  fbo_scale_factor_ = scale_factor;
+  layer_.reset([[ImageTransportLayer alloc] initWithStorageProvider:this]);
+  gfx::Size dip_size(gfx::ToFlooredSize(gfx::ScaleSize(
+      fbo_pixel_size_, 1.0f / scale_factor)));
+  [layer_ setContentsScale:scale_factor];
+  [layer_ setFrame:CGRectMake(0, 0, dip_size.width(), dip_size.height())];
   return true;
 }
 
@@ -157,78 +155,25 @@ void CALayerStorageProvider::FreeColorBufferStorage() {
   fbo_pixel_size_ = gfx::Size();
 }
 
-void CALayerStorageProvider::SwapBuffers(
-    const gfx::Size& size, float scale_factor) {
+uint64 CALayerStorageProvider::GetSurfaceHandle() const {
+  return SurfaceHandleFromCAContextID([context_ contextId]);
+}
+
+void CALayerStorageProvider::WillSwapBuffers() {
   DCHECK(!has_pending_draw_);
   has_pending_draw_ = true;
 
-  // Allocate a CAContext to use to transport the CALayer to the browser
-  // process.
-  if (!context_) {
-    base::scoped_nsobject<NSDictionary> dict([[NSDictionary alloc] init]);
-    CGSConnectionID connection_id = CGSMainConnectionID();
-    context_.reset([CAContext contextWithCGSConnection:connection_id
-                                               options:dict]);
-    [context_ retain];
-  }
-
-  // Allocate a CALayer to use to draw the content.
-  if (!layer_) {
-    layer_.reset([[ImageTransportLayer alloc] initWithStorageProvider:this]);
-    gfx::Size dip_size(gfx::ToFlooredSize(gfx::ScaleSize(
-        fbo_pixel_size_, 1.0f / fbo_scale_factor_)));
-    [layer_ setContentsScale:fbo_scale_factor_];
-    [layer_ setFrame:CGRectMake(0, 0, dip_size.width(), dip_size.height())];
-
-    // Make the CALayer current to the CAContext and display its contents
-    // immediately.
+  // Don't add the layer to the CAContext until a SwapBuffers is going to be
+  // called, because the texture does not have any content until the
+  // SwapBuffers call is about to be made.
+  if ([context_ layer] != layer_.get())
     [context_ setLayer:layer_];
-  }
 
-  // Tell CoreAnimation to draw our frame. We will send the IPC to the browser
-  // when CoreAnimation has drawn our frame.
-  if (gpu_vsync_disabled_) {
-    DrawWithVsyncDisabled();
-  } else {
-    if (![layer_ isAsynchronous])
-      [layer_ setAsynchronous:YES];
-  }
+  if (![layer_ isAsynchronous])
+    [layer_ setAsynchronous:YES];
 }
 
-void CALayerStorageProvider::DrawWithVsyncDisabled() {
-  DCHECK(has_pending_draw_);
-  [layer_ setNeedsDisplay];
-
-  // Sometimes, setNeedsDisplay calls are dropped on the floor. Make this not
-  // hang the renderer by re-issuing the call if the draw has not yet
-  // happened.
-  if (has_pending_draw_) {
-    // Delay sending another draw immediately to avoid starving the run loop.
-    base::MessageLoop::current()->PostDelayedTask(
-        FROM_HERE,
-        base::Bind(&CALayerStorageProvider::DrawWithVsyncDisabled,
-                   weak_factory_.GetWeakPtr()),
-        base::TimeDelta::FromMilliseconds(5));
-  }
-}
-
-void CALayerStorageProvider::WillWriteToBackbuffer() {
-  // TODO(ccameron): The browser may need to continue issuing swaps even when
-  // they do not draw. In these cases it is necessary to either double-buffer
-  // the resulting texture, or to drop frames.
-}
-
-void CALayerStorageProvider::DiscardBackbuffer() {
-  // If this surface's backbuffer is discarded, it is because this surface has
-  // been made non-visible. Ensure that the previous contents are not briefly
-  // flashed when this is made visible by creating a new CALayer and CAContext
-  // at the next swap.
-  [layer_ resetStorageProvider];
-  layer_.reset();
-  context_.reset();
-}
-
-void CALayerStorageProvider::SwapBuffersAckedByBrowser() {
+void CALayerStorageProvider::CanFreeSwappedBuffer() {
 }
 
 CGLContextObj CALayerStorageProvider::LayerShareGroupContext() {
@@ -240,22 +185,20 @@ bool CALayerStorageProvider::LayerCanDraw() {
     can_draw_returned_false_count_ = 0;
     return true;
   } else {
-    if ([layer_ isAsynchronous]) {
-      DCHECK(!gpu_vsync_disabled_);
-      // If we are in asynchronous mode, we will be getting callbacks at every
-      // vsync, asking us if we have anything to draw. If we get 30 of these in
-      // a row, ask that we stop getting these callback for now, so that we
-      // don't waste CPU cycles.
-      if (can_draw_returned_false_count_ == 30)
+    if (can_draw_returned_false_count_ == 30) {
+      if ([layer_ isAsynchronous])
         [layer_ setAsynchronous:NO];
-      else
-        can_draw_returned_false_count_ += 1;
+    } else {
+      can_draw_returned_false_count_ += 1;
     }
     return false;
   }
 }
 
 void CALayerStorageProvider::LayerDoDraw() {
+  DCHECK(has_pending_draw_);
+  has_pending_draw_ = false;
+
   GLint viewport[4] = {0, 0, 0, 0};
   glGetIntegerv(GL_VIEWPORT, viewport);
   gfx::Size viewport_size(viewport[2], viewport[3]);
@@ -290,25 +233,7 @@ void CALayerStorageProvider::LayerDoDraw() {
   glDisable(GL_TEXTURE_RECTANGLE_ARB);
 
   // Allow forward progress in the context now that the swap is complete.
-  DCHECK(has_pending_draw_);
-  SendPendingSwapToBrowserAfterFrameDrawn();
-}
-
-void CALayerStorageProvider::LayerResetStorageProvider() {
-  // If we are providing back-pressure by waiting for a draw, that draw will
-  // now never come, so release the pressure now.
-  SendPendingSwapToBrowserAfterFrameDrawn();
-}
-
-void CALayerStorageProvider::SendPendingSwapToBrowserAfterFrameDrawn() {
-  if (!has_pending_draw_)
-    return;
-  weak_factory_.InvalidateWeakPtrs();
-  has_pending_draw_ = false;
-  transport_surface_->SendSwapBuffers(
-      SurfaceHandleFromCAContextID([context_ contextId]),
-      fbo_pixel_size_,
-      fbo_scale_factor_);
+  transport_surface_->UnblockContextAfterPendingSwap();
 }
 
 }  //  namespace content

content/common/gpu/image_transport_surface_fbo_mac.h

@@ -41,20 +41,20 @@ class ImageTransportSurfaceFBO
     // GL texture that was bound has already been deleted by the caller.
     virtual void FreeColorBufferStorage() = 0;
 
-    // Swap buffers and return the handle for the surface to send to the browser
-    // process to display.
-    virtual void SwapBuffers(const gfx::Size& size, float scale_factor) = 0;
-
-    // Indicate that the backbuffer will be written to.
-    virtual void WillWriteToBackbuffer() = 0;
-
-    // Indicate that the backbuffer has been discarded and should not be seen
-    // again.
-    virtual void DiscardBackbuffer() = 0;
-
-    // Called once for every SwapBuffers call when the IPC for the present has
-    // been processed by the browser.
-    virtual void SwapBuffersAckedByBrowser() = 0;
+    // Retrieve the handle for the surface to send to the browser process to
+    // display.
+    virtual uint64 GetSurfaceHandle() const = 0;
+
+    // Called when a new frame has been rendered into the texture, and the
+    // browser is about to be sent the surface to display.
+    virtual void WillSwapBuffers() = 0;
+
+    // Called once for every WillSwapBuffers call when the buffer that was sent
+    // to the browser may be released by the GPU process (this may be because
+    // the browser is holding a reference, in which case this will come
+    // quickly, or it may be because the browser is done with the surface, in
+    // which case it will come much later).
+    virtual void CanFreeSwappedBuffer() = 0;
   };
 
   ImageTransportSurfaceFBO(GpuChannelManager* manager,
@@ -78,9 +78,7 @@ class ImageTransportSurfaceFBO
   virtual void SetFrontbufferAllocation(bool allocated) OVERRIDE;
 
   // Called when the context may continue to make forward progress after a swap.
-  void SendSwapBuffers(uint64 surface_handle,
-                       const gfx::Size pixel_size,
-                       float scale_factor);
+  void UnblockContextAfterPendingSwap();
 
  protected:
   // ImageTransportSurface implementation
@@ -122,8 +120,12 @@ class ImageTransportSurfaceFBO
   // Whether or not we've successfully made the surface current once.
   bool made_current_;
 
-  // Whether a SwapBuffers IPC needs to be sent to the browser.
-  bool is_swap_buffers_send_pending_;
+  // Whether a SwapBuffers is pending.
+  bool is_swap_buffers_pending_;
+
+  // Whether we unscheduled command buffer because of pending SwapBuffers.
+  bool did_unschedule_;
+
   std::vector<ui::LatencyInfo> latency_info_;
 
   scoped_ptr<ImageTransportHelper> helper_;

content/common/gpu/image_transport_surface_fbo_mac.mm

@@ -28,7 +28,8 @@ ImageTransportSurfaceFBO::ImageTransportSurfaceFBO(
       context_(NULL),
       scale_factor_(1.f),
       made_current_(false),
-      is_swap_buffers_send_pending_(false) {
+      is_swap_buffers_pending_(false),
+      did_unschedule_(false) {
   if (ui::RemoteLayerAPISupported())
     storage_provider_.reset(new CALayerStorageProvider(this));
   else
@@ -61,9 +62,17 @@ void ImageTransportSurfaceFBO::Destroy() {
 }
 
 bool ImageTransportSurfaceFBO::DeferDraws() {
-  storage_provider_->WillWriteToBackbuffer();
-  // We should not have a pending send when we are drawing the next frame.
-  DCHECK(!is_swap_buffers_send_pending_);
+  // The command buffer hit a draw/clear command that could clobber the
+  // IOSurface in use by an earlier SwapBuffers. If a Swap is pending, abort
+  // processing of the command by returning true and unschedule until the Swap
+  // Ack arrives.
+  if(did_unschedule_)
+    return true;  // Still unscheduled, so just return true.
+  if (is_swap_buffers_pending_) {
+    did_unschedule_ = true;
+    helper_->SetScheduled(false);
+    return true;
+  }
   return false;
 }
 
@@ -92,8 +101,6 @@ bool ImageTransportSurfaceFBO::SetBackbufferAllocation(bool allocation) {
     return true;
   backbuffer_suggested_allocation_ = allocation;
   AdjustBufferAllocation();
-  if (!allocation)
-    storage_provider_->DiscardBackbuffer();
   return true;
 }
 
@@ -123,22 +130,18 @@ bool ImageTransportSurfaceFBO::SwapBuffers() {
     return true;
   glFlush();
 
-  // It is the responsibility of the storage provider to send the swap IPC.
-  is_swap_buffers_send_pending_ = true;
-  storage_provider_->SwapBuffers(size_, scale_factor_);
-  return true;
-}
-
-void ImageTransportSurfaceFBO::SendSwapBuffers(uint64 surface_handle,
-                                               const gfx::Size pixel_size,
-                                               float scale_factor) {
   GpuHostMsg_AcceleratedSurfaceBuffersSwapped_Params params;
-  params.surface_handle = surface_handle;
-  params.size = pixel_size;
-  params.scale_factor = scale_factor;
+  params.surface_handle = storage_provider_->GetSurfaceHandle();
+  params.size = GetSize();
+  params.scale_factor = scale_factor_;
   params.latency_info.swap(latency_info_);
   helper_->SendAcceleratedSurfaceBuffersSwapped(params);
-  is_swap_buffers_send_pending_ = false;
+
+  DCHECK(!is_swap_buffers_pending_);
+  is_swap_buffers_pending_ = true;
+
+  storage_provider_->WillSwapBuffers();
+  return true;
 }
 
 bool ImageTransportSurfaceFBO::PostSubBuffer(
@@ -167,7 +170,16 @@ void* ImageTransportSurfaceFBO::GetDisplay() {
 void ImageTransportSurfaceFBO::OnBufferPresented(
     const AcceleratedSurfaceMsg_BufferPresented_Params& params) {
   context_->share_group()->SetRendererID(params.renderer_id);
-  storage_provider_->SwapBuffersAckedByBrowser();
+  storage_provider_->CanFreeSwappedBuffer();
+}
+
+void ImageTransportSurfaceFBO::UnblockContextAfterPendingSwap() {
+  DCHECK(is_swap_buffers_pending_);
+  is_swap_buffers_pending_ = false;
+  if (did_unschedule_) {
+    did_unschedule_ = false;
+    helper_->SetScheduled(true);
+  }
 }
 
 void ImageTransportSurfaceFBO::OnResize(gfx::Size size,

content/common/gpu/image_transport_surface_iosurface_mac.cc

@@ -105,26 +105,21 @@ void IOSurfaceStorageProvider::FreeColorBufferStorage() {
   io_surface_id_ = 0;
 }
 
-void IOSurfaceStorageProvider::SwapBuffers(
-    const gfx::Size& size, float scale_factor) {
+uint64 IOSurfaceStorageProvider::GetSurfaceHandle() const {
+  return SurfaceHandleFromIOSurfaceID(io_surface_id_);
+}
+
+void IOSurfaceStorageProvider::WillSwapBuffers() {
   // The browser compositor will throttle itself, so we are free to unblock the
   // context immediately. Make sure that the browser is doing its throttling
   // appropriately by ensuring that the previous swap was acknowledged before
   // we get another swap.
   DCHECK(pending_swapped_surfaces_.empty());
   pending_swapped_surfaces_.push_back(io_surface_);
-
-  transport_surface_->SendSwapBuffers(
-      SurfaceHandleFromIOSurfaceID(io_surface_id_), size, scale_factor);
-}
-
-void IOSurfaceStorageProvider::WillWriteToBackbuffer() {
-}
-
-void IOSurfaceStorageProvider::DiscardBackbuffer() {
+  transport_surface_->UnblockContextAfterPendingSwap();
 }
 
-void IOSurfaceStorageProvider::SwapBuffersAckedByBrowser() {
+void IOSurfaceStorageProvider::CanFreeSwappedBuffer() {
   DCHECK(!pending_swapped_surfaces_.empty());
   pending_swapped_surfaces_.pop_front();
 }

content/common/gpu/image_transport_surface_iosurface_mac.h

@@ -28,10 +28,9 @@ class IOSurfaceStorageProvider
       CGLContextObj context, GLuint texture,
       gfx::Size pixel_size, float scale_factor) OVERRIDE;
   virtual void FreeColorBufferStorage() OVERRIDE;
-  virtual void SwapBuffers(const gfx::Size& size, float scale_factor) OVERRIDE;
-  virtual void WillWriteToBackbuffer() OVERRIDE;
-  virtual void DiscardBackbuffer() OVERRIDE;
-  virtual void SwapBuffersAckedByBrowser() OVERRIDE;
+  virtual uint64 GetSurfaceHandle() const OVERRIDE;
+  virtual void WillSwapBuffers() OVERRIDE;
+  virtual void CanFreeSwappedBuffer() OVERRIDE;
 
  private:
   ImageTransportSurfaceFBO* transport_surface_;

ui/compositor/compositor.cc

@@ -276,10 +276,6 @@ void Compositor::SetBackgroundColor(SkColor color) {
   ScheduleDraw();
 }
 
-void Compositor::SetVisible(bool visible) {
-  host_->SetVisible(visible);
-}
-
 scoped_refptr<CompositorVSyncManager> Compositor::vsync_manager() const {
   return vsync_manager_;
 }

ui/compositor/compositor.h

@@ -186,9 +186,6 @@ class COMPOSITOR_EXPORT Compositor
   // the |root_layer|.
   void SetBackgroundColor(SkColor color);
 
-  // Set the visibility of the underlying compositor.
-  void SetVisible(bool visible);
-
   // Returns the widget for this compositor.
   gfx::AcceleratedWidget widget() const { return widget_; }
 

ui/gl/gl_gl_api_implementation.cc

@@ -492,13 +492,4 @@ void VirtualGLApi::glFinishFn() {
   GLApiBase::SignalFlush();
 }
 
-ScopedSetGLToRealGLApi::ScopedSetGLToRealGLApi()
-    : old_gl_api_(GetCurrentGLApi()) {
-  SetGLToRealGLApi();
-}
-
-ScopedSetGLToRealGLApi::~ScopedSetGLToRealGLApi() {
-  SetGLApi(old_gl_api_);
-}
-
 }  // namespace gfx

ui/gl/gl_gl_api_implementation.h

@@ -7,7 +7,6 @@
 
 #include "base/compiler_specific.h"
 #include "ui/gl/gl_bindings.h"
-#include "ui/gl/gl_export.h"
 
 namespace gpu {
 namespace gles2 {
@@ -118,15 +117,6 @@ private:
   std::string extensions_;
 };
 
-class GL_EXPORT ScopedSetGLToRealGLApi {
- public:
-  ScopedSetGLToRealGLApi();
-  ~ScopedSetGLToRealGLApi();
-
- private:
-  GLApi* old_gl_api_;
-};
-
 }  // namespace gfx
 
 #endif  // UI_GL_GL_GL_API_IMPLEMENTATION_H_