Enable asynchronous glReadPixels on Windows.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index c7fab686353c00671275af1f55d6f70938779f3e..58e742e69c751bd914a4d988b3e7b6dc0aa0fc41 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -7538,10 +7538,12 @@ void GLES2DecoderImpl::FinishReadPixels(
     if (buffer != 0) {
       glDeleteBuffersARB(1, &buffer);
     }
+    if (result)
+      *result = GL_INVALID_VALUE;
     return;
   }
 
-  if (buffer != 0) {
+  if (buffer != 0) {  // Asynchronous readback path.
     glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, buffer);
     void* data;
     if (features().map_buffer_range) {
@@ -7550,16 +7552,17 @@ void GLES2DecoderImpl::FinishReadPixels(
     } else {
       data = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY);
     }
-    memcpy(pixels, data, pixels_size);
+    if (result)
+      *result = glGetError();
+    if (data)
+      memcpy(pixels, data, pixels_size);
     // GL_PIXEL_PACK_BUFFER_ARB is currently unused, so we don't
     // have to restore the state.
     glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB);
     glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 0);
     glDeleteBuffersARB(1, &buffer);
-  }
-
-  if (result != NULL) {
-    *result = true;
+    if (!data)
+      return;
   }
 
   GLenum read_format = GetBoundReadFrameBufferInternalFormat();
@@ -7574,6 +7577,8 @@ void GLES2DecoderImpl::FinishReadPixels(
     if (!GLES2Util::ComputeImageDataSizes(
             width, 2, format, type, state_.pack_alignment, &temp_size,
             &unpadded_row_size, &padded_row_size)) {
+      if (result)
+        *result = GL_INVALID_VALUE;
       return;
     }
 
@@ -7751,17 +7756,25 @@ error::Error GLES2DecoderImpl::HandleReadPixels(uint32 immediate_data_size,
       GLuint buffer = 0;
       glGenBuffersARB(1, &buffer);
       glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, buffer);
-      glBufferData(GL_PIXEL_PACK_BUFFER_ARB, pixels_size, NULL, GL_STREAM_READ);
+      // For ANGLE client version 2, GL_STREAM_READ is not available.
+      const GLenum usage_hint =
+          features().is_angle ? GL_STATIC_DRAW : GL_STREAM_READ;
+      glBufferData(GL_PIXEL_PACK_BUFFER_ARB, pixels_size, NULL, usage_hint);
       GLenum error = glGetError();
       if (error == GL_NO_ERROR) {
         glReadPixels(x, y, width, height, format, type, 0);
-        pending_readpixel_fences_.push(linked_ptr<FenceCallback>(
-            new FenceCallback()));
-        WaitForReadPixels(base::Bind(
-            &GLES2DecoderImpl::FinishReadPixels,
-            base::internal::SupportsWeakPtrBase::StaticAsWeakPtr
-            <GLES2DecoderImpl>(this),
-            c, buffer));
+        error = glGetError();
+        if (result)
+          *result = error;
+        if (error == GL_NO_ERROR) {
+          pending_readpixel_fences_.push(linked_ptr<FenceCallback>(
+              new FenceCallback()));
+          WaitForReadPixels(base::Bind(
+              &GLES2DecoderImpl::FinishReadPixels,
+              base::internal::SupportsWeakPtrBase::StaticAsWeakPtr
+              <GLES2DecoderImpl>(this),
+              c, buffer));
+        }
         glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 0);
         return error::kNoError;
       } else {
@@ -7772,13 +7785,11 @@ error::Error GLES2DecoderImpl::HandleReadPixels(uint32 immediate_data_size,
     }
     glReadPixels(x, y, width, height, format, type, pixels);
   }
-  GLenum error = LOCAL_PEEK_GL_ERROR("glReadPixels");
-  if (error == GL_NO_ERROR) {
-    if (result != NULL) {
-      *result = true;
-    }
+  const GLenum error = LOCAL_PEEK_GL_ERROR("glReadPixels");
+  if (result)
+    *result = error;
+  if (error == GL_NO_ERROR)
     FinishReadPixels(c, 0);
-  }
 
   return error::kNoError;
 }