Add WebGraphicsContext support for readbacks from any framebuffer.

content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc

Index: content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
diff --git a/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc b/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
index 88f1505f814157ad7b1443f8b8dfb02c05192e5e..5a4ce7766cce4e4ba9d94716c1df8aced5d96837 100644
--- a/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
+++ b/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
@@ -253,8 +253,11 @@ void WebGraphicsContext3DCommandBufferImpl::FlipVertically(
 
 bool WebGraphicsContext3DCommandBufferImpl::readBackFramebuffer(
     unsigned char* pixels,
-    size_t buffer_size) {
-  if (buffer_size != static_cast<size_t>(4 * width() * height())) {
+    int width,
+    int height,
+    size_t buffer_size,
+    WebGLId buffer) {
+  if (buffer_size != static_cast<size_t>(4 * width * height)) {
     return false;
   }
 
@@ -265,11 +268,11 @@ bool WebGraphicsContext3DCommandBufferImpl::readBackFramebuffer(
   // vertical flip is only a temporary solution anyway until Chrome
   // is fully GPU composited, it wasn't worth the complexity.
 
-  bool mustRestoreFBO = (bound_fbo_ != 0);
+  bool mustRestoreFBO = (bound_fbo_ != buffer);
   if (mustRestoreFBO) {
-    gl_->BindFramebuffer(GL_FRAMEBUFFER, 0);
+    gl_->BindFramebuffer(GL_FRAMEBUFFER, buffer);
   }

[Ken Russell (switch to Gerrit), 2011/08/04 22:55:07]

Do you think we might want or need checks about the completeness of the FBO
given that it's now coming from outside code?

[jbauman, 2011/08/04 23:20:21]

Those can be expensive, so I'd rather avoid them (even if they aren't as
expensive as the actual readpixels). I'll let the calling code take care of
that, so they'll be done less often.

-   gl_->ReadPixels(0, 0, cached_width_, cached_height_,
+   gl_->ReadPixels(0, 0, width, height,
                    GL_RGBA, GL_UNSIGNED_BYTE, pixels);
 
   // Swizzle red and blue channels
@@ -284,13 +287,19 @@ bool WebGraphicsContext3DCommandBufferImpl::readBackFramebuffer(
 
 #ifdef FLIP_FRAMEBUFFER_VERTICALLY
   if (pixels) {
-    FlipVertically(pixels, cached_width_, cached_height_);
+    FlipVertically(pixels, width, height);
   }
 #endif
 
   return true;
 }
 
+bool WebGraphicsContext3DCommandBufferImpl::readBackFramebuffer(
+    unsigned char* pixels,
+    size_t buffer_size) {
+  return readBackFramebuffer(pixels, width(), height(), buffer_size, 0);
+}
+
 void WebGraphicsContext3DCommandBufferImpl::synthesizeGLError(
     WGC3Denum error) {
   if (find(synthetic_errors_.begin(), synthetic_errors_.end(), error) ==