AndroidVDA by using Android's MediaCodec API.

content/common/gpu/media/gles2_external_texture_copier.cc

+// Copyright (c) 2013 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/media/gles2_external_texture_copier.h"
+
+#include "base/logging.h"
+
+namespace content {
+
+static void CheckGlError(const char* op) {
+#ifndef NDEBUG
+  for (GLint error = glGetError(); error; error = glGetError()) {
+    LOG(ERROR) << "after " << op <<" glError (0x" << std::hex << error << ")";
+    NOTREACHED();
+  }
+#endif
+}
+
+Gles2ExternalTextureCopier::Gles2ExternalTextureCopier(
+    int32 width, int32 height)
+  : width_(width),

[greggman, 2013/02/20 19:13:58]

style nit: 4 spaces in front of :

[dwkang1, 2013/02/25 23:48:00]

Done.

+    height_(height) {
+  SaveState();
+  copier_.Initialize();
+  RestoreState();
+}
+
+Gles2ExternalTextureCopier::~Gles2ExternalTextureCopier() {
+  copier_.Destroy();
+}
+
+bool Gles2ExternalTextureCopier::Copy(
+    GLuint source_texture_id, GLuint destination_texture_id_) {
+  SaveState();
+  glViewport(0, 0, width_, height_);
+  copier_.DoCopyTexture(
+      GL_TEXTURE_2D, source_texture_id, destination_texture_id_, 0,
+      false, false, false, true);
+  RestoreState();
+  return true;
+}
+
+void Gles2ExternalTextureCopier::SaveState() {
+  // TODO(dwkang): Reportedly, glGetXXXs are extremely slow on some platforms.
+  //               Check if we can skip some of below or find out a way to get
+  //               the status from GLES2Decoder().
+  glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previous_framebuffer_id_);
+  glGetIntegerv(GL_RENDERBUFFER_BINDING, &previous_renderbuffer_id_);

[greggman, 2013/02/20 19:13:58]

render buffers are not used by copy

[dwkang1, 2013/02/25 23:48:00]

Done.

+  glGetIntegerv(GL_TEXTURE_BINDING_2D, &previous_texture_2d_id_);

[greggman, 2013/02/20 19:13:58]

CopyTextureCHROMIUMResourceManager::DoCopyTexture calls glActiveTexture and uses
texture unit 0. That means you need to query the active texture unit. You then
need to call glActiveTexture(GL_TEXTURE0) before you query the
GL_TEXTURE_BINDING_2D query.  You'll also need to restore in the opposite order.
First restore the binding then restore the active texture unit back to the unit
it was at

[dwkang1, 2013/02/25 23:48:00]

Done.

+  glGetIntegerv(GL_CURRENT_PROGRAM, &previous_program_);
+  glGetIntegerv(GL_VIEWPORT, previous_viewport_);
+  glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &vertex_array_buffer_binding_);
+  glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, &index_array_buffer_binding_);
+

[greggman, 2013/02/20 19:13:58]

You also need to query/restore GL_DEPTH_TEST, GL_SCISSOR_TEST, GL_STENCIL_TEST,
GL_CULL_FACE, glColorMask, glDepthMask, GL_BLEND and you need to query 

[dwkang1, 2013/02/25 23:48:00]

Done.

+  SaveStateForAttrib(
+      CopyTextureCHROMIUMResourceManager::kVertexPositionAttrib, 0);
+  SaveStateForAttrib(
+      CopyTextureCHROMIUMResourceManager::kVertexTextureAttrib, 1);
+  CheckGlError("SaveState");

[greggman, 2013/02/20 19:13:58]

You also need to query and restore the Texture Parameters GL_TEXTURE_WRAP_S,
GL_TEXTURE_WRAP_T, GL_TEXTURE_MAG_FILTER, and GL_TEXTURE_MIN_FILTER for your
source and dest textures.

[dwkang1, 2013/02/25 23:48:00]

The doc says glTexParameter sets params for the active texture unit. So, I
believe they should be restored when we restore the state of GL_TEXTURE0. Please
correct me if I am wrong.
http://www.opengl.org/sdk/docs/man/xhtml/glTexParameter.xml
"glTexParameter specifies the texture parameters for the active texture unit,
specified by calling glActiveTexture."

+}
+
+void Gles2ExternalTextureCopier::RestoreState() {
+  glBindFramebufferEXT(GL_FRAMEBUFFER, previous_framebuffer_id_);
+  glBindRenderbufferEXT(GL_RENDERBUFFER, previous_renderbuffer_id_);
+  glBindTexture(GL_TEXTURE_2D, previous_texture_2d_id_);
+  glUseProgram(previous_program_);

[greggman, 2013/02/20 19:13:58]

Note: Querying and restoring bindings can never work correctly. The reason is
resources are ref counted. So, if any of these resources were deleted in another
context their only reference is their binding in this context. When they get
unbound, by binding something new in
CopyTextureCHROMIUMResourceManager::DoCopyTexture, they are released and these
bindings trying to restore them will fail.

Yet another reason why query and restore does not work in GL.

[dwkang1, 2013/02/25 23:48:00]

I added a TODO message for it.

+  glViewport(previous_viewport_[0], previous_viewport_[1],
+             previous_viewport_[2], previous_viewport_[3]);
+  glBindBuffer(GL_ARRAY_BUFFER, vertex_array_buffer_binding_);
+  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_array_buffer_binding_);
+
+  RestoreStateForAttrib(
+      CopyTextureCHROMIUMResourceManager::kVertexPositionAttrib, 0);
+  RestoreStateForAttrib(
+      CopyTextureCHROMIUMResourceManager::kVertexTextureAttrib, 1);
+  CheckGlError("RestoreState");
+}
+
+void Gles2ExternalTextureCopier::SaveStateForAttrib(
+    GLuint attrib, int index) {
+  glGetVertexAttribiv(attrib, GL_VERTEX_ATTRIB_ARRAY_ENABLED,
+                      &previous_vertex_attrib_[index].enabled);
+  glGetVertexAttribiv(attrib, GL_VERTEX_ATTRIB_ARRAY_SIZE,
+                      &previous_vertex_attrib_[index].size);
+  glGetVertexAttribiv(attrib, GL_VERTEX_ATTRIB_ARRAY_TYPE,
+                      &previous_vertex_attrib_[index].type);
+  glGetVertexAttribiv(attrib, GL_VERTEX_ATTRIB_ARRAY_NORMALIZED,
+                      &previous_vertex_attrib_[index].normalized);
+  glGetVertexAttribiv(attrib, GL_VERTEX_ATTRIB_ARRAY_STRIDE,
+                      &previous_vertex_attrib_[index].stride);
+  glGetVertexAttribPointerv(attrib, GL_VERTEX_ATTRIB_ARRAY_POINTER,
+                            &previous_vertex_attrib_[index].pointer);
+}
+
+void Gles2ExternalTextureCopier::RestoreStateForAttrib(
+    GLuint attrib, int index) {
+  glVertexAttribPointer(
+      attrib,
+      previous_vertex_attrib_[index].size,
+      previous_vertex_attrib_[index].type,
+      previous_vertex_attrib_[index].normalized,
+      previous_vertex_attrib_[index].stride,
+      previous_vertex_attrib_[index].pointer);
+
+  if (previous_vertex_attrib_[index].enabled)
+    glEnableVertexAttribArray(attrib);
+  else
+    glDisableVertexAttribArray(attrib);
+}
+
+}  // namespace content