Implement GLHelperReadbackSupport for GLHelper usage.

content/common/gpu/client/gl_helper_readback_support.cc

+// Copyright (c) 2014 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_readback_support.h"
+#include "base/logging.h"
+
+namespace content {
+
+GLHelperReadbackSupport::GLHelperReadbackSupport(gpu::gles2::GLES2Interface* gl,
+                                                 GLHelper* helper)
+    : gl_(gl), helper_(helper) {
+  InitializeReadbackSupport();
+}
+
+GLHelperReadbackSupport::~GLHelperReadbackSupport() {}
+
+void GLHelperReadbackSupport::InitializeReadbackSupport() {
+  // We are concerned about 16, 32-bit formats only.
+  // The below are the most used 16, 32-bit formats.
+  // In future if any new format support is needed that should be added here.
+  // Initialize the array with FORMAT_NOT_SUPPORTED as we dont know the
+  // supported formats yet.
+  for (int i = 0; i < SkBitmap::kConfigCount; ++i) {
+    format_support_table_[i] = FORMAT_NOT_SUPPORTED;
+  }
+  CheckForReadbackSupport(SkBitmap::kRGB_565_Config);
+  CheckForReadbackSupport(SkBitmap::kARGB_4444_Config);
+  CheckForReadbackSupport(SkBitmap::kARGB_8888_Config);
+  // Further any formats, support should be checked here.
+}
+
+void GLHelperReadbackSupport::CheckForReadbackSupport(
+    SkBitmap::Config texture_format) {
+  bool supports_format = false;
+  switch (texture_format) {
+    case SkBitmap::kRGB_565_Config:
+      supports_format = SupportsFormat(GL_RGB, GL_UNSIGNED_SHORT_5_6_5);
+      break;
+    case SkBitmap::kARGB_8888_Config:
+      supports_format = SupportsFormat(GL_RGBA, GL_UNSIGNED_BYTE);
+      break;
+    case SkBitmap::kARGB_4444_Config:
+      supports_format = false;
+      break;
+    default:
+      NOTREACHED();
+      supports_format = false;
+      break;
+  }

[no sievers, 2014/02/28 19:25:53]

just to be paranoid since you use SkBitmap::Config as an index:
DCHECK(texture_format < arraysize(format_support_table_));

[sivag, 2014/03/04 09:46:45]

Done.

+  format_support_table_[texture_format] =
+      supports_format ? FORMAT_SUPPORTED : FORMAT_NOT_SUPPORTED;
+}
+
+bool GLHelperReadbackSupport::SupportsFormat(GLint format, GLint type) {
+  const int kTestSize = 64;
+  GLuint dst_texture = 0u;
+  bool supports_format = false;
+  gl_->GenTextures(1, &dst_texture);

[no sievers, 2014/02/28 19:25:53]

nit: instead of Gen/Delete you can use ScopedTexture here, since you are also
using ScopedFramebuffer below.

[sivag, 2014/03/04 09:46:45]

Done.

+  ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(gl_, dst_texture);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+  gl_->TexImage2D(
+      GL_TEXTURE_2D, 0, format, kTestSize, kTestSize, 0, format, type, NULL);
+  ScopedFramebuffer dst_framebuffer(gl_);
+  ScopedFramebufferBinder<GL_FRAMEBUFFER> framebuffer_binder(gl_,
+                                                             dst_framebuffer);
+  gl_->FramebufferTexture2D(
+      GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, dst_texture, 0);
+  GLint ext_format = 0, ext_type = 0;
+  gl_->GetIntegerv(GL_IMPLEMENTATION_COLOR_READ_FORMAT, &ext_format);
+  gl_->GetIntegerv(GL_IMPLEMENTATION_COLOR_READ_TYPE, &ext_type);
+  gl_->DeleteTextures(1, &dst_texture);
+  if ((ext_format == format) && (ext_type == type)) {
+    supports_format = true;
+  }
+  return supports_format;
+}
+
+bool GLHelperReadbackSupport::IsReadbackConfigSupported(
+    SkBitmap::Config texture_format) {
+  switch (format_support_table_[texture_format]) {
+    case FORMAT_SUPPORTED:
+      return true;
+    case FORMAT_NOT_SUPPORTED:

[no sievers, 2014/02/28 19:25:53]

case FORMAT_NOT_SUPPORTED:
  return false;
default:
  NOTREACHED();
  return false;

[sivag, 2014/03/04 09:46:45]

Done.

[sivag, 2014/03/04 09:46:45]

Done.

+    default:
+      return false;
+  }
+}
+
+}  // namespace content