Implement client side PBOs for glReadPixel

content/common/gpu/client/gl_helper.cc

 // Copyright (c) 2012 The Chromium 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 "content/common/gpu/client/gl_helper.h"
 
 #include <queue>
 
 #include "base/bind.h"
+#include "base/debug/trace_event.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
-#include "base/memory/ref_counted.h"
 #include "base/message_loop.h"
-#include "base/synchronization/lock.h"
-#include "base/synchronization/waitable_event.h"
-#include "base/threading/thread.h"
-#include "base/threading/thread_restrictions.h"
+#include "base/time.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebCString.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebString.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/size.h"
 #include "ui/gl/gl_bindings.h"
 
 using WebKit::WebGLId;
 using WebKit::WebGraphicsContext3D;
 
 namespace {
 
-const char kGLHelperThreadName[] = "GLHelperThread";
-
-class GLHelperThread : public base::Thread {
- public:
-  GLHelperThread() : base::Thread(kGLHelperThreadName) {
-    Start();
-  }
-  virtual ~GLHelperThread() {
-    Stop();
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(GLHelperThread);
-};
-
-base::LazyInstance<GLHelperThread> g_gl_helper_thread =
-    LAZY_INSTANCE_INITIALIZER;
-
 class ScopedWebGLId {
  public:
   typedef void (WebGraphicsContext3D::*DeleteFunc)(WebGLId);
   ScopedWebGLId(WebGraphicsContext3D* context,
                 WebGLId id,
                 DeleteFunc delete_func)
       : context_(context),
         id_(id),
         delete_func_(delete_func) {
   }
@@ skipping 34 matching lines @@
 
 class ScopedFramebuffer : public ScopedWebGLId {
  public:
   ScopedFramebuffer(WebGraphicsContext3D* context,
                     WebGLId id)
       : ScopedWebGLId(context,
                       id,
                       &WebGraphicsContext3D::deleteFramebuffer) {}
 };
 
-class ScopedRenderbuffer : public ScopedWebGLId {
- public:
-  ScopedRenderbuffer(WebGraphicsContext3D* context,
-                     WebGLId id)
-      : ScopedWebGLId(context,
-                      id,
-                      &WebGraphicsContext3D::deleteRenderbuffer) {}
-};
-
 class ScopedProgram : public ScopedWebGLId {
  public:
   ScopedProgram(WebGraphicsContext3D* context,
                 WebGLId id)
       : ScopedWebGLId(context,
                       id,
                       &WebGraphicsContext3D::deleteProgram) {}
 };
 
 class ScopedShader : public ScopedWebGLId {
@@ skipping 16 matching lines @@
 
 template <WebKit::WGC3Denum target>
 class ScopedBinder {
  public:
   typedef void (WebGraphicsContext3D::*BindFunc)(WebKit::WGC3Denum,
                                                          WebGLId);
   ScopedBinder(WebGraphicsContext3D* context,
                WebGLId id,
                BindFunc bind_func)
       : context_(context),
-        id_(id),
         bind_func_(bind_func) {
-    (context_->*bind_func_)(target, id_);
+    (context_->*bind_func_)(target, id);
   }
 
   virtual ~ScopedBinder() {
-    if (id_ != 0)
-      (context_->*bind_func_)(target, 0);
+    (context_->*bind_func_)(target, 0);
   }
 
  private:
   WebGraphicsContext3D* context_;
-  WebGLId id_;
   BindFunc bind_func_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedBinder);
 };
 
 template <WebKit::WGC3Denum target>
 class ScopedBufferBinder : ScopedBinder<target> {
  public:
   ScopedBufferBinder(WebGraphicsContext3D* context,
                      WebGLId id)
       : ScopedBinder<target>(
           context,
           id,
           &WebGraphicsContext3D::bindBuffer) {}
 };
 
 template <WebKit::WGC3Denum target>
 class ScopedFramebufferBinder : ScopedBinder<target> {
  public:
   ScopedFramebufferBinder(WebGraphicsContext3D* context,
                           WebGLId id)
       : ScopedBinder<target>(
           context,
           id,
           &WebGraphicsContext3D::bindFramebuffer) {}
 };
 
 template <WebKit::WGC3Denum target>
-class ScopedRenderbufferBinder : ScopedBinder<target> {
- public:
-  ScopedRenderbufferBinder(WebGraphicsContext3D* context,
-                           WebGLId id)
-      : ScopedBinder<target>(
-          context,
-          id,
-          &WebGraphicsContext3D::bindRenderbuffer) {}
-};
-
-template <WebKit::WGC3Denum target>
 class ScopedTextureBinder : ScopedBinder<target> {
  public:
   ScopedTextureBinder(WebGraphicsContext3D* context,
                       WebGLId id)
       : ScopedBinder<target>(
           context,
           id,
           &WebGraphicsContext3D::bindTexture) {}
 };
 
 class ScopedFlush {
  public:
   explicit ScopedFlush(WebGraphicsContext3D* context)
       : context_(context) {
   }
 
   virtual ~ScopedFlush() {
     context_->flush();
   }
 
  private:
   WebGraphicsContext3D* context_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedFlush);
 };
 
-void DeleteContext(WebGraphicsContext3D* context) {
-  delete context;
-}
-
-void SignalWaitableEvent(base::WaitableEvent* event) {
-  event->Signal();
-}
-
 }  // namespace
 
 namespace content {
 
 // Implements GLHelper::CropScaleReadbackAndCleanTexture and encapsulates the
 // data needed for it.
-class GLHelper::CopyTextureToImpl {
+class GLHelper::CopyTextureToImpl :
+      public base::SupportsWeakPtr<GLHelper::CopyTextureToImpl> {
  public:
   CopyTextureToImpl(WebGraphicsContext3D* context,
-                    WebGraphicsContext3D* context_for_thread,
                     GLHelper* helper)
       : context_(context),
-        context_for_thread_(context_for_thread),
         helper_(helper),
         flush_(context),
         program_(context, context->createProgram()),
         vertex_attributes_buffer_(context_, context_->createBuffer()),
         flipped_vertex_attributes_buffer_(context_, context_->createBuffer()) {
     InitBuffer();
     InitProgram();
   }
   ~CopyTextureToImpl() {
     CancelRequests();
-    DeleteContextForThread();
   }
 
   void InitBuffer();
   void InitProgram();
 
   void CropScaleReadbackAndCleanTexture(
       WebGLId src_texture,
       const gfx::Size& src_size,
       const gfx::Rect& src_subrect,
       const gfx::Size& dst_size,
       unsigned char* out,
       const base::Callback<void(bool)>& callback);
 
   void ReadbackTextureSync(WebGLId texture,
                            const gfx::Rect& src_rect,
                            unsigned char* out);
 
   WebKit::WebGLId CopyAndScaleTexture(WebGLId texture,
                                       const gfx::Size& src_size,
                                       const gfx::Size& dst_size,
                                       bool vertically_flip_texture);
 
  private:
   // A single request to CropScaleReadbackAndCleanTexture.
-  // Thread-safety notes: the main thread creates instances of this class. The
-  // main thread can cancel the request, before it's handled by the helper
+  // The main thread can cancel the request, before it's handled by the helper
   // thread, by resetting the texture and pixels fields. Alternatively, the
   // thread marks that it handles the request by resetting the pixels field
   // (meaning it guarantees that the callback with be called).
   // In either case, the callback must be called exactly once, and the texture
   // must be deleted by the main thread context.
-  struct Request : public base::RefCountedThreadSafe<Request> {
-    Request(CopyTextureToImpl* impl,
-            WebGLId texture_,
+  struct Request {
+    Request(WebGLId texture_,
             const gfx::Size& size_,
             unsigned char* pixels_,
             const base::Callback<void(bool)>& callback_)
-        : copy_texture_impl(impl),
-        size(size_),
-        callback(callback_),
-        lock(),
-        texture(texture_),
-        pixels(pixels_) {
+        : size(size_),
+          callback(callback_),
+          texture(texture_),
+          pixels(pixels_),
+          buffer(0),
+          query(0) {
     }
 
-    // These members are only accessed on the main thread.
-    GLHelper::CopyTextureToImpl* copy_texture_impl;
     gfx::Size size;
     base::Callback<void(bool)> callback;
 
-    // Locks access to below members, which can be accessed on any thread.
-    base::Lock lock;
     WebGLId texture;
     unsigned char* pixels;
-
-   private:
-    friend class base::RefCountedThreadSafe<Request>;
-    ~Request() {}
+    GLuint buffer;
+    GLuint query;
   };
 
   // Copies the block of pixels specified with |src_subrect| from |src_texture|,
   // scales it to |dst_size|, writes it into a texture, and returns its ID.
   // |src_size| is the size of |src_texture|.
   WebGLId ScaleTexture(WebGLId src_texture,
                        const gfx::Size& src_size,
                        const gfx::Rect& src_subrect,
                        const gfx::Size& dst_size,
                        bool vertically_flip_texture);
 
-  // Deletes the context for GLHelperThread.
-  void DeleteContextForThread();
-  static void ReadBackFramebuffer(scoped_refptr<Request> request,
-                                  WebGraphicsContext3D* context,
-                                  scoped_refptr<base::TaskRunner> reply_loop);
-  static void ReadBackFramebufferComplete(scoped_refptr<Request> request,
-                                          bool result);
-  void FinishRequest(scoped_refptr<Request> request);
+  void ScheduleCheckReadbackDone();
+  void CheckReadbackDone();
+  void FinishRequest(Request* request, bool result);
   void CancelRequests();
 
   // Interleaved array of 2-dimentional vertex positions (x, y) and
   // 2-dimentional texture coordinates (s, t).
   static const WebKit::WGC3Dfloat kVertexAttributes[];
   // Interleaved array of 2-dimensional vertex positions (x, y) and
   // 2 dimensional texture coordinates (s, t).
   static const WebKit::WGC3Dfloat kFlippedVertexAttributes[];
   // Shader sources used for GLHelper::CropScaleReadbackAndCleanTexture and
   // GLHelper::ReadbackTextureSync
   static const WebKit::WGC3Dchar kCopyVertexShader[];
   static const WebKit::WGC3Dchar kCopyFragmentShader[];
 
   WebGraphicsContext3D* context_;
-  WebGraphicsContext3D* context_for_thread_;
   GLHelper* helper_;
 
   // A scoped flush that will ensure all resource deletions are flushed when
   // this object is destroyed. Must be declared before other Scoped* fields.
   ScopedFlush flush_;
   // A program for copying a source texture into a destination texture.
   ScopedProgram program_;
   // The buffer that holds the vertices and the texture coordinates data for
   // drawing a quad.
   ScopedBuffer vertex_attributes_buffer_;
   ScopedBuffer flipped_vertex_attributes_buffer_;
 
   // The location of the position in the program.
   WebKit::WGC3Dint position_location_;
   // The location of the texture coordinate in the program.
   WebKit::WGC3Dint texcoord_location_;
   // The location of the source texture in the program.
   WebKit::WGC3Dint texture_location_;
   // The location of the texture coordinate of the sub-rectangle in the program.
   WebKit::WGC3Dint src_subrect_location_;
-  std::queue<scoped_refptr<Request> > request_queue_;
+  std::queue<Request*> request_queue_;
 };
 
 const WebKit::WGC3Dfloat GLHelper::CopyTextureToImpl::kVertexAttributes[] = {
   -1.0f, -1.0f, 0.0f, 0.0f,
   1.0f, -1.0f, 1.0f, 0.0f,
   -1.0f, 1.0f, 0.0f, 1.0f,
   1.0f, 1.0f, 1.0f, 1.0f,
 };
 
 const WebKit::WGC3Dfloat
 GLHelper::CopyTextureToImpl::kFlippedVertexAttributes[] = {
   -1.0f, -1.0f, 0.0f, 1.0f,
   1.0f, -1.0f, 1.0f, 1.0f,
   -1.0f, 1.0f, 0.0f, 0.0f,
   1.0f, 1.0f, 1.0f, 0.0f,
 };
 
 const WebKit::WGC3Dchar GLHelper::CopyTextureToImpl::kCopyVertexShader[] =
     "attribute vec2 a_position;"
     "attribute vec2 a_texcoord;"
     "varying vec2 v_texcoord;"
     "uniform vec4 src_subrect;"
     "void main() {"
     "  gl_Position = vec4(a_position, 0.0, 1.0);"
     "  v_texcoord = src_subrect.xy + a_texcoord * src_subrect.zw;"
     "}";
 
+
+#if (SK_R32_SHIFT == 16) && !SK_B32_SHIFT
 const WebKit::WGC3Dchar GLHelper::CopyTextureToImpl::kCopyFragmentShader[] =
     "precision mediump float;"
     "varying vec2 v_texcoord;"
+    "uniform sampler2D s_texture;"
+    "void main() {"
+    "  gl_FragColor = texture2D(s_texture, v_texcoord).bgra;"
+    "}";
+#else
+const WebKit::WGC3Dchar GLHelper::CopyTextureToImpl::kCopyFragmentShader[] =
+    "precision mediump float;"
+    "varying vec2 v_texcoord;"
     "uniform sampler2D s_texture;"
     "void main() {"
     "  gl_FragColor = texture2D(s_texture, v_texcoord);"
     "}";
+#endif
+
 
 void GLHelper::CopyTextureToImpl::InitBuffer() {
   ScopedBufferBinder<GL_ARRAY_BUFFER> buffer_binder(
       context_, vertex_attributes_buffer_);
   context_->bufferData(GL_ARRAY_BUFFER,
                        sizeof(kVertexAttributes),
                        kVertexAttributes,
                        GL_STATIC_DRAW);
   ScopedBufferBinder<GL_ARRAY_BUFFER> flipped_buffer_binder(
       context_, flipped_vertex_attributes_buffer_);
@@ skipping 30 matching lines @@
 
 WebGLId GLHelper::CopyTextureToImpl::ScaleTexture(
     WebGLId src_texture,
     const gfx::Size& src_size,
     const gfx::Rect& src_subrect,
     const gfx::Size& dst_size,
     bool vertically_flip_texture) {
   WebGLId dst_texture = context_->createTexture();
   {
     ScopedFramebuffer dst_framebuffer(context_, context_->createFramebuffer());
-    ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(
-        context_, dst_framebuffer);
+    ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(context_,
+                                                               dst_framebuffer);
     {
-      ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(
-          context_, dst_texture);
+      ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(context_, dst_texture);
       context_->texImage2D(GL_TEXTURE_2D,
                            0,
                            GL_RGBA,
                            dst_size.width(),
                            dst_size.height(),
                            0,
                            GL_RGBA,
                            GL_UNSIGNED_BYTE,
                            NULL);
       context_->framebufferTexture2D(GL_FRAMEBUFFER,
                                      GL_COLOR_ATTACHMENT0,
                                      GL_TEXTURE_2D,
                                      dst_texture,
                                      0);
     }
 
     ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(context_, src_texture);
     WebKit::WebGLId vertex_attributes_buffer = vertically_flip_texture ?
         flipped_vertex_attributes_buffer_ : vertex_attributes_buffer_;
-    ScopedBufferBinder<GL_ARRAY_BUFFER> buffer_binder(
-        context_, vertex_attributes_buffer);
+    ScopedBufferBinder<GL_ARRAY_BUFFER> buffer_binder(context_,
+                                                      vertex_attributes_buffer);
 
     context_->viewport(0, 0, dst_size.width(), dst_size.height());
     context_->useProgram(program_);
 
     WebKit::WGC3Dintptr offset = 0;
     context_->vertexAttribPointer(position_location_,
                                   2,
                                   GL_FLOAT,
                                   GL_FALSE,
                                   4 * sizeof(WebKit::WGC3Dfloat),
@@ skipping 20 matching lines @@
     };
 
     context_->uniform4fv(src_subrect_location_, 1, src_subrect_texcoord);
 
     // Conduct texture mapping by drawing a quad composed of two triangles.
     context_->drawArrays(GL_TRIANGLE_STRIP, 0, 4);
   }
   return dst_texture;
 }
 
-void GLHelper::CopyTextureToImpl::DeleteContextForThread() {
-  if (!context_for_thread_)
-    return;
-
-  g_gl_helper_thread.Pointer()->message_loop_proxy()->PostTask(
-      FROM_HERE,
-      base::Bind(&DeleteContext,
-                 context_for_thread_));
-  context_for_thread_ = NULL;
-}
-
 void GLHelper::CopyTextureToImpl::CropScaleReadbackAndCleanTexture(
     WebGLId src_texture,
     const gfx::Size& src_size,
     const gfx::Rect& src_subrect,
     const gfx::Size& dst_size,
     unsigned char* out,
     const base::Callback<void(bool)>& callback) {
-  if (!context_for_thread_) {
-    callback.Run(false);
-    return;
-  }
-
   WebGLId texture = ScaleTexture(src_texture,
                                  src_size,
                                  src_subrect,
                                  dst_size,
-                                 false);
+#ifdef USE_SKIA

[piman, 2013/03/28 20:22:27]

?
What does USE_SKIA mean? All platforms use skia...
I also don't see where it's even defined anywhere.

[hubbe, 2013/03/28 20:52:35]

It seems that USE_SKIA is beinging erased from history.
I based this on code that is no longer there.
(see
http://src.chromium.org/viewvc/chrome/trunk/src/content/common/gpu/client/web...)

I'm removing it.

+                                 true
+#else
+                                 false
+#endif
+                                 );
   context_->flush();
-  scoped_refptr<Request> request =
-      new Request(this, texture, dst_size, out, callback);
+  Request* request = new Request(texture, dst_size, out, callback);
   request_queue_.push(request);
+  if (request_queue_.size() == 1) {
+    ScheduleCheckReadbackDone();
+  }
 
-  g_gl_helper_thread.Pointer()->message_loop_proxy()->PostTask(FROM_HERE,
-      base::Bind(&ReadBackFramebuffer,
-                 request,
-                 context_for_thread_,
-                 base::MessageLoopProxy::current()));
+  ScopedFlush flush(context_);
+  ScopedFramebuffer dst_framebuffer(context_, context_->createFramebuffer());
+  gfx::Size size;
+  size = request->size;
+
+  ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(context_,
+                                                             dst_framebuffer);
+  ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(context_, request->texture);
+  context_->framebufferTexture2D(GL_FRAMEBUFFER,
+                                 GL_COLOR_ATTACHMENT0,
+                                 GL_TEXTURE_2D,
+                                 request->texture,
+                                 0);
+  request->buffer = context_->createBuffer();
+  context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM,
+                       request->buffer);
+  context_->bufferData(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM,
+                       4 * size.GetArea(),
+                       NULL,
+                       GL_STREAM_READ);
+
+  request->query = context_->createQueryEXT();
+  context_->beginQueryEXT(GL_COMMANDS_ISSUED_CHROMIUM, request->query);
+  context_->readPixels(0, 0, size.width(), size.height(),
+                       GL_RGBA, GL_UNSIGNED_BYTE, 0);
+  context_->endQueryEXT(GL_COMMANDS_ISSUED_CHROMIUM);
+  context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM, 0);
+
 }
 
 void GLHelper::CopyTextureToImpl::ReadbackTextureSync(WebGLId texture,
                                                       const gfx::Rect& src_rect,
                                                       unsigned char* out) {
   ScopedFramebuffer dst_framebuffer(context_, context_->createFramebuffer());
-  ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(
-      context_, dst_framebuffer);
+  ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(context_,
+                                                             dst_framebuffer);
   ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(context_, texture);
   context_->framebufferTexture2D(GL_FRAMEBUFFER,
                                  GL_COLOR_ATTACHMENT0,
                                  GL_TEXTURE_2D,
                                  texture,
                                  0);
   context_->readPixels(src_rect.x(),
                        src_rect.y(),
                        src_rect.width(),
                        src_rect.height(),
                        GL_RGBA,
                        GL_UNSIGNED_BYTE,
                        out);
 }
 
 WebKit::WebGLId GLHelper::CopyTextureToImpl::CopyAndScaleTexture(
     WebGLId src_texture,
     const gfx::Size& src_size,
     const gfx::Size& dst_size,
     bool vertically_flip_texture) {
   return ScaleTexture(src_texture,
                       src_size,
                       gfx::Rect(src_size),
                       dst_size,
                       vertically_flip_texture);
 }
 
-void GLHelper::CopyTextureToImpl::ReadBackFramebuffer(
-    scoped_refptr<Request> request,
-    WebGraphicsContext3D* context,
-    scoped_refptr<base::TaskRunner> reply_loop) {
-  DCHECK(context);
-  if (!context->makeContextCurrent() || context->isContextLost()) {
-    base::AutoLock auto_lock(request->lock);
-    if (request->pixels) {
-      // Only report failure if the request wasn't canceled (otherwise the
-      // failure has already been reported).
-      request->pixels = NULL;
-      reply_loop->PostTask(
-          FROM_HERE, base::Bind(ReadBackFramebufferComplete, request, false));
-    }
-    return;
-  }
-  ScopedFlush flush(context);
-  ScopedFramebuffer dst_framebuffer(context, context->createFramebuffer());
-  unsigned char* pixels = NULL;
-  gfx::Size size;
-  {
-    // Note: We don't want to keep the lock while doing the readBack (since we
-    // don't want to block the UI thread). We rely on the fact that once the
-    // texture is bound to a FBO (that isn't current), deleting the texture is
-    // delayed until the FBO is deleted. We ensure ordering by flushing while
-    // the lock is held. Either the main thread cancelled before we get the
-    // lock, and we'll exit early, or we ensure that the texture is bound to the
-    // framebuffer before the main thread has a chance to delete it.
-    base::AutoLock auto_lock(request->lock);
-    if (!request->texture || !request->pixels)
-      return;
-    pixels = request->pixels;
-    request->pixels = NULL;
-    size = request->size;
-    {
-      ScopedFlush flush(context);
-      ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(
-          context, dst_framebuffer);
-      ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(
-          context, request->texture);
-      context->framebufferTexture2D(GL_FRAMEBUFFER,
-                                    GL_COLOR_ATTACHMENT0,
-                                    GL_TEXTURE_2D,
-                                    request->texture,
-                                    0);
-    }
-  }
-  bool result = context->readBackFramebuffer(
-        pixels,
-        4 * size.GetArea(),
-        dst_framebuffer.id(),
-        size.width(),
-        size.height());
-  reply_loop->PostTask(
-      FROM_HERE, base::Bind(ReadBackFramebufferComplete, request, result));
+
+void GLHelper::CopyTextureToImpl::ScheduleCheckReadbackDone() {
+  DCHECK(!request_queue_.empty());
+  base::MessageLoopProxy::current()->PostDelayedTask(
+      FROM_HERE,
+      base::Bind(&CopyTextureToImpl::CheckReadbackDone, AsWeakPtr()),
+      base::TimeDelta::FromMilliseconds(2));

[piman, 2013/03/28 20:22:27]

Rather than a poll (with a completely arbitrary 2ms), we have a mechanism to get
an asynchronous completion callback, with sync points.
I realize it's only exposed on CommandBufferProxyImpl, not directly on
WebGraphicsContext3D, but it seems that it's just a matter of exposing this, and
we'd have a much more efficient signaling mechanism.

[hubbe, 2013/03/28 20:52:35]

Excellent. But how? Do you have a pointer or an example?
If difficult, can I make this a TODO()?

[piman, 2013/03/28 21:10:06]

It's not difficult per se.
The call is CommandBufferProxyImpl::SignalSyncPoint. You first insert a sync
point using context_->insertSyncPoint (think, like a command buffer token, but
that also works cross-command buffer), and you use SignalSyncPoint so that the
GPU process sends you a callback once the sync point has passed.

The only thing is, as it's not exposed on WebGraphicsContext3D, we need to add
it there, as well as an implementation in WebGraphicsContext3DCommandBufferImpl
(that just forwards to its CommandBufferProxyImpl), so that you can use it here.

The advantage is you save all the code related to queries and polling, and you
also save at run-time by not having to poll on arbitrary intervals. I think it's
well worth doing.

 }
 
-void GLHelper::CopyTextureToImpl::ReadBackFramebufferComplete(
-    scoped_refptr<Request> request,
-    bool result) {
-  request->callback.Run(result);
-  if (request->copy_texture_impl)
-    request->copy_texture_impl->FinishRequest(request);
+void GLHelper::CopyTextureToImpl::CheckReadbackDone() {
+  TRACE_EVENT0("mirror",
+               "GLHelper::CopyTextureToImpl::CheckReadBackFramebufferComplete");
+  while (!request_queue_.empty()) {
+    Request* request = request_queue_.front();
+
+    bool result = false;
+    if (request->buffer != 0) {
+      unsigned int done = 1;
+      context_->getQueryObjectuivEXT(request->query,
+                                     GL_QUERY_RESULT_AVAILABLE_EXT, &done);
+      if (!done) {
+        ScheduleCheckReadbackDone();
+        return;
+      }
+      context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM,
+                           request->buffer);
+      void* data = context_->mapBufferCHROMIUM(
+          GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM, GL_READ_ONLY);
+
+      if (data) {
+        result = true;
+        memcpy(request->pixels, data, request->size.GetArea() * 4);
+        context_->unmapBufferCHROMIUM(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM);
+      }
+      context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM, 0);
+    }
+
+    FinishRequest(request, result);
+  }
 }
 
-void GLHelper::CopyTextureToImpl::FinishRequest(
-    scoped_refptr<Request> request) {
-  CHECK(request_queue_.front() == request);
+void GLHelper::CopyTextureToImpl::FinishRequest(Request* request, bool result) {
+  DCHECK(request_queue_.front() == request);
   request_queue_.pop();
-  base::AutoLock auto_lock(request->lock);
+  request->callback.Run(result);
+  ScopedFlush flush(context_);
   if (request->texture != 0) {
     context_->deleteTexture(request->texture);
     request->texture = 0;
-    context_->flush();
   }
+  if (request->buffer != 0) {
+    context_->deleteBuffer(request->buffer);
+    request->buffer = 0;
+  }
+  if (request->query != 0) {
+    context_->deleteQueryEXT(request->query);
+    request->query = 0;
+  }
+  delete request;
 }
 
 void GLHelper::CopyTextureToImpl::CancelRequests() {
   while (!request_queue_.empty()) {
-    scoped_refptr<Request> request = request_queue_.front();
-    request_queue_.pop();
-    request->copy_texture_impl = NULL;
-    bool cancelled = false;
-    {
-      base::AutoLock auto_lock(request->lock);
-      if (request->texture != 0) {
-        context_->deleteTexture(request->texture);
-        request->texture = 0;
-      }
-      if (request->pixels != NULL) {
-        request->pixels = NULL;
-        cancelled = true;
-      }
-    }
-    if (cancelled)
-      request->callback.Run(false);
+    Request* request = request_queue_.front();
+    FinishRequest(request, false);
   }
 }
 
-base::subtle::Atomic32 GLHelper::count_ = 0;
-
-GLHelper::GLHelper(WebGraphicsContext3D* context,
-                   WebGraphicsContext3D* context_for_thread)
-    : context_(context),
-      context_for_thread_(context_for_thread) {
-  base::subtle::NoBarrier_AtomicIncrement(&count_, 1);
+GLHelper::GLHelper(WebGraphicsContext3D* context)
+    : context_(context) {
 }
 
 GLHelper::~GLHelper() {
-  DCHECK_NE(MessageLoop::current(),
-            g_gl_helper_thread.Pointer()->message_loop());
-  base::subtle::Atomic32 decremented_count =
-    base::subtle::NoBarrier_AtomicIncrement(&count_, -1);
-  if (decremented_count == 0) {
-    // When this is the last instance, we synchronize with the pending
-    // operations on GLHelperThread. Otherwise on shutdown we may kill the GPU
-    // process infrastructure (BrowserGpuChannelHostFactory) before they have
-    // a chance to complete, likely leading to a crash.
-    base::WaitableEvent event(false, false);
-    g_gl_helper_thread.Pointer()->message_loop_proxy()->PostTask(
-        FROM_HERE,
-        base::Bind(&SignalWaitableEvent,
-                   &event));
-    // http://crbug.com/125415
-    base::ThreadRestrictions::ScopedAllowWait allow_wait;
-    event.Wait();
-  }
 }
 
 WebGraphicsContext3D* GLHelper::context() const {
   return context_;
 }
 
 void GLHelper::CropScaleReadbackAndCleanTexture(
     WebGLId src_texture,
     const gfx::Size& src_size,
     const gfx::Rect& src_subrect,
@@ skipping 49 matching lines @@
   if (!compile_status) {
     LOG(ERROR) << std::string(context_->getShaderInfoLog(shader).utf8());
     return 0;
   }
   return shader.Detach();
 }
 
 void GLHelper::InitCopyTextToImpl() {
   // Lazily initialize |copy_texture_to_impl_|
   if (!copy_texture_to_impl_.get())
-    copy_texture_to_impl_.reset(new CopyTextureToImpl(context_,
-                                                      context_for_thread_,
-                                                      this));
+    copy_texture_to_impl_.reset(new CopyTextureToImpl(context_, this));
 }
 
 void GLHelper::CopySubBufferDamage(WebKit::WebGLId texture,
                                    WebKit::WebGLId previous_texture,
                                    const SkRegion& new_damage,
                                    const SkRegion& old_damage) {
   SkRegion region(old_damage);
   if (region.op(new_damage, SkRegion::kDifference_Op)) {
     ScopedFramebuffer dst_framebuffer(context_, context_->createFramebuffer());
-    ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(
-        context_, dst_framebuffer);
+    ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(context_,
+                                                               dst_framebuffer);
     ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(context_, texture);
     context_->framebufferTexture2D(GL_FRAMEBUFFER,
                                    GL_COLOR_ATTACHMENT0,
                                    GL_TEXTURE_2D,
                                    previous_texture,
                                    0);
     for (SkRegion::Iterator it(region); !it.done(); it.next()) {
       const SkIRect& rect = it.rect();
       context_->copyTexSubImage2D(GL_TEXTURE_2D, 0,
                                   rect.x(), rect.y(),
                                   rect.x(), rect.y(),
                                   rect.width(), rect.height());
     }
     context_->flush();
   }
 }
 
 }  // namespace content