src/cobalt/renderer/backend/egl/graphics_context.cc - cobalt - Git at Google

 /*
  * Copyright 2015 Google Inc. All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include <GLES2/gl2.h>
 #include <algorithm>

 #include "cobalt/renderer/backend/egl/graphics_context.h"

 #include "base/debug/trace_event.h"
 #include "cobalt/base/polymorphic_downcast.h"
 #include "cobalt/renderer/backend/egl/graphics_system.h"
 #include "cobalt/renderer/backend/egl/texture.h"
 #include "cobalt/renderer/backend/egl/texture_data.h"
 #include "cobalt/renderer/backend/egl/utils.h"

 namespace cobalt {
 namespace renderer {
 namespace backend {

 namespace {

 bool HasExtension(const char* extension) {
   const char* raw_extension_string =
       reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS));
   DCHECK(raw_extension_string);

   return strstr(raw_extension_string, extension) != NULL;
 }

 }  // namespace

 GraphicsContextEGL::GraphicsContextEGL(GraphicsSystem* parent_system,
                                        EGLDisplay display, EGLConfig config,
                                        ResourceContext* resource_context)
     : GraphicsContext(parent_system),
       display_(display),
       config_(config),
       is_current_(false) {
 #if defined(GLES3_SUPPORTED)
   context_ = CreateGLES3Context(display, config, resource_context->context());
 #else
   // Create an OpenGL ES 2.0 context.
   EGLint context_attrib_list[] = {
       EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE,
   };
   context_ =
       eglCreateContext(display, config, EGL_NO_CONTEXT, context_attrib_list);
   CHECK_EQ(EGL_SUCCESS, eglGetError());
 #endif

   // Create a dummy EGLSurface object to be assigned as the target surface
   // when we need to make OpenGL calls that do not depend on a surface (e.g.
   // creating a texture).
   null_surface_ = new PBufferRenderTargetEGL(display, config, math::Size(1, 1));

   ScopedMakeCurrent scoped_current_context(this);

   bgra_format_supported_ = HasExtension("GL_EXT_texture_format_BGRA8888");

   SetupBlitObjects();
 }

 GraphicsSystemEGL* GraphicsContextEGL::system_egl() {
   return base::polymorphic_downcast<GraphicsSystemEGL*>(system());
 }

 bool GraphicsContextEGL::ComputeReadPixelsNeedVerticalFlip() {
   // Create a 1x2 texture with distinct values vertically so that we can test
   // them.  We will blit the texture to an offscreen render target, and then
   // read back the value of the render target's pixels to check if they are
   // flipped or not.  It is found that the results of this test can differ
   // between at least Angle and Mesa GL, so if the results of this test are not
   // taken into account, one of those platforms will read pixels out upside
   // down.
   const int kDummyTextureWidth = 1;
   const int kDummyTextureHeight = 2;

   scoped_refptr<RenderTarget> render_target = CreateOffscreenRenderTarget(
       math::Size(kDummyTextureWidth, kDummyTextureHeight));
   scoped_refptr<PBufferRenderTargetEGL> render_target_egl = make_scoped_refptr(
       base::polymorphic_downcast<PBufferRenderTargetEGL*>(render_target.get()));
   {
     ScopedMakeCurrent scoped_make_current(this, render_target_egl);

     // Create a 2-pixel texture and then immediately blit it to our 2-pixel
     // framebuffer render target.
     GLuint texture;
     GL_CALL(glGenTextures(1, &texture));
     GL_CALL(glBindTexture(GL_TEXTURE_2D, texture));
     SetupInitialTextureParameters();

     uint8_t pixels[8];
     pixels[0] = 0;
     pixels[1] = 0;
     pixels[2] = 0;
     pixels[3] = 0;
     pixels[4] = 255;
     pixels[5] = 255;
     pixels[6] = 255;
     pixels[7] = 255;

     GL_CALL(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, kDummyTextureWidth,
                          kDummyTextureHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE,
                          pixels));
     GL_CALL(glBindTexture(GL_TEXTURE_2D, 0));

     Blit(texture, 0, 0, kDummyTextureWidth, kDummyTextureHeight);
     GL_CALL(glDeleteTextures(1, &texture));
     GL_CALL(glFinish());
   }

   // Now read back the texture data using glReadPixels().
   scoped_ptr<TextureEGL> render_target_texture(
       new TextureEGL(this, render_target_egl));

   GLuint framebuffer;
   GL_CALL(glGenFramebuffers(1, &framebuffer));
   GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, framebuffer));

   GL_CALL(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                                  GL_TEXTURE_2D,
                                  render_target_texture->gl_handle(), 0));

   uint32_t out_data[2];
   GL_CALL(glReadPixels(0, 0, kDummyTextureWidth, kDummyTextureHeight, GL_RGBA,
                        GL_UNSIGNED_BYTE, out_data));

   GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, 0));
   GL_CALL(glDeleteFramebuffers(1, &framebuffer));

   // Ensure the data is in one of two possible states, flipped or not flipped.
   DCHECK((out_data[0] == 0x00000000 && out_data[1] == 0xFFFFFFFF) ||
          (out_data[0] == 0xFFFFFFFF && out_data[1] == 0x00000000));

   // Finally check if the data we read back was flipped or not.
   return out_data[1] == 0x00000000;
 }

 void GraphicsContextEGL::SetupBlitObjects() {
   // Setup shaders used when blitting the current texture.
   blit_program_ = glCreateProgram();

   blit_vertex_shader_ = glCreateShader(GL_VERTEX_SHADER);
   const char* blit_vertex_shader_source =
       "attribute vec2 a_position;"
       "attribute vec2 a_tex_coord;"
       "varying vec2 v_tex_coord;"
       "void main() {"
       "  gl_Position = vec4(a_position.x, a_position.y, 0, 1);"
       "  v_tex_coord = a_tex_coord;"
       "}";
   int blit_vertex_shader_source_length = strlen(blit_vertex_shader_source);
   GL_CALL(glShaderSource(blit_vertex_shader_, 1, &blit_vertex_shader_source,
                          &blit_vertex_shader_source_length));
   GL_CALL(glCompileShader(blit_vertex_shader_));
   GL_CALL(glAttachShader(blit_program_, blit_vertex_shader_));

   blit_fragment_shader_ = glCreateShader(GL_FRAGMENT_SHADER);
   const char* blit_fragment_shader_source =
       "precision mediump float;"
       "varying vec2 v_tex_coord;"
       "uniform sampler2D texture;"
       "void main() {"
       "  gl_FragColor = texture2D(texture, v_tex_coord);"
       "}";
   int blit_fragment_shader_source_length = strlen(blit_fragment_shader_source);
   GL_CALL(glShaderSource(blit_fragment_shader_, 1, &blit_fragment_shader_source,
                          &blit_fragment_shader_source_length));
   GL_CALL(glCompileShader(blit_fragment_shader_));
   GL_CALL(glAttachShader(blit_program_, blit_fragment_shader_));

   GL_CALL(glBindAttribLocation(
       blit_program_, kBlitPositionAttribute, "a_position"));
   GL_CALL(glBindAttribLocation(
       blit_program_, kBlitTexcoordAttribute, "a_tex_coord"));

   GL_CALL(glLinkProgram(blit_program_));

   // Setup a vertex buffer that can blit a quad with a full texture, to be used
   // by Frame::BlitToRenderTarget().
   struct QuadVertex {
     float position_x;
     float position_y;
     float tex_coord_u;
     float tex_coord_v;
   };
   const QuadVertex kBlitQuadVerts[4] = {
       {-1.0f, -1.0f, 0.0f, 1.0f},
       {-1.0f, 1.0f, 0.0f, 0.0f},
       {1.0f, -1.0f, 1.0f, 1.0f},
       {1.0f, 1.0, 1.0f, 0.0f},
   };
   GL_CALL(glGenBuffers(1, &blit_vertex_buffer_));
   GL_CALL(glBindBuffer(GL_ARRAY_BUFFER, blit_vertex_buffer_));
   GL_CALL(glBufferData(GL_ARRAY_BUFFER, sizeof(kBlitQuadVerts), kBlitQuadVerts,
                        GL_STATIC_DRAW));
 }

 GraphicsContextEGL::~GraphicsContextEGL() {
   MakeCurrent();
   GL_CALL(glDeleteBuffers(1, &blit_vertex_buffer_));
   GL_CALL(glDeleteProgram(blit_program_));
   GL_CALL(glDeleteShader(blit_fragment_shader_));
   GL_CALL(glDeleteShader(blit_vertex_shader_));

   ReleaseCurrentContext();

   null_surface_ = NULL;

   EGL_CALL(eglDestroyContext(display_, context_));
 }

 void GraphicsContextEGL::MakeCurrentWithSurface(RenderTargetEGL* surface) {
   DCHECK_NE(EGL_NO_SURFACE, surface) <<
       "Use ReleaseCurrentContext().";

   EGLSurface egl_surface = surface->GetSurface();
   EGL_CALL(eglMakeCurrent(display_, egl_surface, egl_surface, context_));

   if (surface->IsWindowRenderTarget() && !surface->has_been_made_current()) {
     SecurityClear();
   }
   surface->set_has_been_made_current();

   is_current_ = true;
   current_surface_ = surface;
 }

 void GraphicsContextEGL::MakeCurrent() {
   MakeCurrentWithSurface(null_surface_);
 }

 void GraphicsContextEGL::ReleaseCurrentContext() {
   EGL_CALL(eglMakeCurrent(
       display_, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT));

   current_surface_ = NULL;
   is_current_ = false;
 }

 scoped_ptr<TextureEGL> GraphicsContextEGL::CreateTexture(
     scoped_ptr<TextureDataEGL> texture_data) {
   return make_scoped_ptr(
       new TextureEGL(this, texture_data.Pass(), bgra_format_supported_));
 }

 scoped_ptr<TextureEGL> GraphicsContextEGL::CreateTextureFromRawMemory(
     const scoped_refptr<ConstRawTextureMemoryEGL>& raw_texture_memory,
     intptr_t offset, const math::Size& size, GLenum format,
     int pitch_in_bytes) {
   const RawTextureMemoryEGL* texture_memory =
       &(raw_texture_memory->raw_texture_memory());

   return make_scoped_ptr(new TextureEGL(this, texture_memory, offset, size,
                                         format, pitch_in_bytes,
                                         bgra_format_supported_));
 }

 scoped_refptr<RenderTarget> GraphicsContextEGL::CreateOffscreenRenderTarget(
     const math::Size& dimensions) {
   scoped_refptr<RenderTarget> render_target(new PBufferRenderTargetEGL(
       display_, config_, dimensions));

   return render_target;
 }

 namespace {
 void VerticallyFlipPixels(uint8_t* pixels, int pitch_in_bytes, int height) {
   int half_height = height / 2;
   for (int row = 0; row < half_height; ++row) {
     uint8_t* top_row = pixels + row * pitch_in_bytes;
     uint8_t* bottom_row =
         pixels + (height - 1 - row) * pitch_in_bytes;
     for (int i = 0; i < pitch_in_bytes; ++i) {
       std::swap(top_row[i], bottom_row[i]);
     }
   }
 }
 }  // namespace

 scoped_array<uint8_t> GraphicsContextEGL::DownloadPixelDataAsRGBA(
     const scoped_refptr<RenderTarget>& render_target) {
   TRACE_EVENT0("cobalt::renderer",
                "GraphicsContextEGL::DownloadPixelDataAsRGBA()");

   PBufferRenderTargetEGL* pbuffer_render_target =
       base::polymorphic_downcast<PBufferRenderTargetEGL*>(render_target.get());

   scoped_ptr<TextureEGL> texture(new TextureEGL(this, pbuffer_render_target));

   ScopedMakeCurrent scoped_current_context(this);

   // This shouldn't be strictly necessary as glReadPixels() should implicitly
   // call glFinish(), however it doesn't hurt to be safe and guard against
   // potentially different implementations.  Performance is not an issue
   // in this function, because it is only used by tests to verify rendered
   // output.
   GL_CALL(glFinish());

   GLuint texture_framebuffer;
   GL_CALL(glGenFramebuffers(1, &texture_framebuffer));
   GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, texture_framebuffer));

   GL_CALL(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                                  GL_TEXTURE_2D, texture->gl_handle(), 0));
   DCHECK_EQ(GL_FRAMEBUFFER_COMPLETE, glCheckFramebufferStatus(GL_FRAMEBUFFER));

   int pitch_in_bytes =
       texture->GetSize().width() * BytesPerPixelForGLFormat(GL_RGBA);

   scoped_array<uint8_t> pixels(
       new uint8_t[texture->GetSize().height() * pitch_in_bytes]);
   GL_CALL(glReadPixels(0, 0, texture->GetSize().width(),
                        texture->GetSize().height(), GL_RGBA, GL_UNSIGNED_BYTE,
                        pixels.get()));

   GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, 0));
   GL_CALL(glDeleteFramebuffers(1, &texture_framebuffer));

   // Vertically flip the resulting pixel data before returning so that the 0th
   // pixel is at the top-left.  While this is not a fast procedure, this
   // entire function is only intended to be used in debug/test code.
   if (!read_pixels_needs_vertical_flip_) {
     // Lazily compute whether we need to vertically flip our read back pixels
     // or not.
     read_pixels_needs_vertical_flip_ = ComputeReadPixelsNeedVerticalFlip();
   }

   if (*read_pixels_needs_vertical_flip_) {
     // Some platforms, like the Mesa Gallium EGL implementation on Linux, seem
     // to return already flipped pixels.  So in that case, we flip them again
     // before returning here.
     VerticallyFlipPixels(pixels.get(), pitch_in_bytes,
                          texture->GetSize().height());
   }

   return pixels.Pass();
 }

 void GraphicsContextEGL::Blit(GLuint texture, int x, int y, int width,
                               int height) {
   // Render a texture to the specified output rectangle on the render target.
   GL_CALL(glViewport(x, y, width, height));
   GL_CALL(glScissor(x, y, width, height));

   GL_CALL(glUseProgram(blit_program_));

   GL_CALL(glBindBuffer(GL_ARRAY_BUFFER, blit_vertex_buffer_));
   GL_CALL(glVertexAttribPointer(kBlitPositionAttribute, 2, GL_FLOAT, GL_FALSE,
                                 sizeof(float) * 4, 0));
   GL_CALL(glVertexAttribPointer(kBlitTexcoordAttribute, 2, GL_FLOAT, GL_FALSE,
                                 sizeof(float) * 4,
                                 reinterpret_cast<GLvoid*>(sizeof(float) * 2)));
   GL_CALL(glEnableVertexAttribArray(kBlitPositionAttribute));
   GL_CALL(glEnableVertexAttribArray(kBlitTexcoordAttribute));

   GL_CALL(glActiveTexture(GL_TEXTURE0));
   GL_CALL(glBindTexture(GL_TEXTURE_2D, texture));

   GL_CALL(glDisable(GL_BLEND));

   GL_CALL(glDrawArrays(GL_TRIANGLE_STRIP, 0, 4));

   GL_CALL(glBindTexture(GL_TEXTURE_2D, 0));

   GL_CALL(glDisableVertexAttribArray(kBlitTexcoordAttribute));
   GL_CALL(glDisableVertexAttribArray(kBlitPositionAttribute));
   GL_CALL(glUseProgram(0));
 }

 void GraphicsContextEGL::SwapBuffers(RenderTargetEGL* surface) {
   TRACE_EVENT0("cobalt::renderer", "GraphicsContextEGL::SwapBuffers()");

   EGL_CALL(eglSwapBuffers(display_, surface->GetSurface()));

   surface->increment_swap_count();
   if (surface->IsWindowRenderTarget() && surface->swap_count() <= 2) {
     SecurityClear();
   }
 }

 void GraphicsContextEGL::SecurityClear() {
   // Clear the screen to a color that is bright and gross to exaggerate that
   // this is a problem if it is witnessed.
   GL_CALL(glClearColor(1.0f, 0.4f, 1.0f, 1.0f));
   GL_CALL(glClear(GL_COLOR_BUFFER_BIT));
 }

 }  // namespace backend
 }  // namespace renderer
 }  // namespace cobalt
	/*
	* Copyright 2015 Google Inc. All Rights Reserved.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include <GLES2/gl2.h>
	#include <algorithm>

	#include "cobalt/renderer/backend/egl/graphics_context.h"

	#include "base/debug/trace_event.h"
	#include "cobalt/base/polymorphic_downcast.h"
	#include "cobalt/renderer/backend/egl/graphics_system.h"
	#include "cobalt/renderer/backend/egl/texture.h"
	#include "cobalt/renderer/backend/egl/texture_data.h"
	#include "cobalt/renderer/backend/egl/utils.h"

	namespace cobalt {
	namespace renderer {
	namespace backend {

	namespace {

	bool HasExtension(const char* extension) {
	const char* raw_extension_string =
	reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS));
	DCHECK(raw_extension_string);

	return strstr(raw_extension_string, extension) != NULL;
	}

	} // namespace

	GraphicsContextEGL::GraphicsContextEGL(GraphicsSystem* parent_system,
	EGLDisplay display, EGLConfig config,
	ResourceContext* resource_context)
	: GraphicsContext(parent_system),
	display_(display),
	config_(config),
	is_current_(false) {
	#if defined(GLES3_SUPPORTED)
	context_ = CreateGLES3Context(display, config, resource_context->context());
	#else
	// Create an OpenGL ES 2.0 context.
	EGLint context_attrib_list[] = {
	EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE,
	};
	context_ =
	eglCreateContext(display, config, EGL_NO_CONTEXT, context_attrib_list);
	CHECK_EQ(EGL_SUCCESS, eglGetError());
	#endif

	// Create a dummy EGLSurface object to be assigned as the target surface
	// when we need to make OpenGL calls that do not depend on a surface (e.g.
	// creating a texture).
	null_surface_ = new PBufferRenderTargetEGL(display, config, math::Size(1, 1));

	ScopedMakeCurrent scoped_current_context(this);

	bgra_format_supported_ = HasExtension("GL_EXT_texture_format_BGRA8888");

	SetupBlitObjects();
	}

	GraphicsSystemEGL* GraphicsContextEGL::system_egl() {
	return base::polymorphic_downcast<GraphicsSystemEGL*>(system());
	}

	bool GraphicsContextEGL::ComputeReadPixelsNeedVerticalFlip() {
	// Create a 1x2 texture with distinct values vertically so that we can test
	// them. We will blit the texture to an offscreen render target, and then
	// read back the value of the render target's pixels to check if they are
	// flipped or not. It is found that the results of this test can differ
	// between at least Angle and Mesa GL, so if the results of this test are not
	// taken into account, one of those platforms will read pixels out upside
	// down.
	const int kDummyTextureWidth = 1;
	const int kDummyTextureHeight = 2;

	scoped_refptr<RenderTarget> render_target = CreateOffscreenRenderTarget(
	math::Size(kDummyTextureWidth, kDummyTextureHeight));
	scoped_refptr<PBufferRenderTargetEGL> render_target_egl = make_scoped_refptr(
	base::polymorphic_downcast<PBufferRenderTargetEGL*>(render_target.get()));
	{
	ScopedMakeCurrent scoped_make_current(this, render_target_egl);

	// Create a 2-pixel texture and then immediately blit it to our 2-pixel
	// framebuffer render target.
	GLuint texture;
	GL_CALL(glGenTextures(1, &texture));
	GL_CALL(glBindTexture(GL_TEXTURE_2D, texture));
	SetupInitialTextureParameters();

	uint8_t pixels[8];
	pixels[0] = 0;
	pixels[1] = 0;
	pixels[2] = 0;
	pixels[3] = 0;
	pixels[4] = 255;
	pixels[5] = 255;
	pixels[6] = 255;
	pixels[7] = 255;

	GL_CALL(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, kDummyTextureWidth,
	kDummyTextureHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE,
	pixels));
	GL_CALL(glBindTexture(GL_TEXTURE_2D, 0));

	Blit(texture, 0, 0, kDummyTextureWidth, kDummyTextureHeight);
	GL_CALL(glDeleteTextures(1, &texture));
	GL_CALL(glFinish());
	}

	// Now read back the texture data using glReadPixels().
	scoped_ptr<TextureEGL> render_target_texture(
	new TextureEGL(this, render_target_egl));

	GLuint framebuffer;
	GL_CALL(glGenFramebuffers(1, &framebuffer));
	GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, framebuffer));

	GL_CALL(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
	GL_TEXTURE_2D,
	render_target_texture->gl_handle(), 0));

	uint32_t out_data[2];
	GL_CALL(glReadPixels(0, 0, kDummyTextureWidth, kDummyTextureHeight, GL_RGBA,
	GL_UNSIGNED_BYTE, out_data));

	GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, 0));
	GL_CALL(glDeleteFramebuffers(1, &framebuffer));

	// Ensure the data is in one of two possible states, flipped or not flipped.
	DCHECK((out_data[0] == 0x00000000 && out_data[1] == 0xFFFFFFFF) \|\|
	(out_data[0] == 0xFFFFFFFF && out_data[1] == 0x00000000));

	// Finally check if the data we read back was flipped or not.
	return out_data[1] == 0x00000000;
	}

	void GraphicsContextEGL::SetupBlitObjects() {
	// Setup shaders used when blitting the current texture.
	blit_program_ = glCreateProgram();

	blit_vertex_shader_ = glCreateShader(GL_VERTEX_SHADER);
	const char* blit_vertex_shader_source =
	"attribute vec2 a_position;"
	"attribute vec2 a_tex_coord;"
	"varying vec2 v_tex_coord;"
	"void main() {"
	" gl_Position = vec4(a_position.x, a_position.y, 0, 1);"
	" v_tex_coord = a_tex_coord;"
	"}";
	int blit_vertex_shader_source_length = strlen(blit_vertex_shader_source);
	GL_CALL(glShaderSource(blit_vertex_shader_, 1, &blit_vertex_shader_source,
	&blit_vertex_shader_source_length));
	GL_CALL(glCompileShader(blit_vertex_shader_));
	GL_CALL(glAttachShader(blit_program_, blit_vertex_shader_));

	blit_fragment_shader_ = glCreateShader(GL_FRAGMENT_SHADER);
	const char* blit_fragment_shader_source =
	"precision mediump float;"
	"varying vec2 v_tex_coord;"
	"uniform sampler2D texture;"
	"void main() {"
	" gl_FragColor = texture2D(texture, v_tex_coord);"
	"}";
	int blit_fragment_shader_source_length = strlen(blit_fragment_shader_source);
	GL_CALL(glShaderSource(blit_fragment_shader_, 1, &blit_fragment_shader_source,
	&blit_fragment_shader_source_length));
	GL_CALL(glCompileShader(blit_fragment_shader_));
	GL_CALL(glAttachShader(blit_program_, blit_fragment_shader_));

	GL_CALL(glBindAttribLocation(
	blit_program_, kBlitPositionAttribute, "a_position"));
	GL_CALL(glBindAttribLocation(
	blit_program_, kBlitTexcoordAttribute, "a_tex_coord"));

	GL_CALL(glLinkProgram(blit_program_));

	// Setup a vertex buffer that can blit a quad with a full texture, to be used
	// by Frame::BlitToRenderTarget().
	struct QuadVertex {
	float position_x;
	float position_y;
	float tex_coord_u;
	float tex_coord_v;
	};
	const QuadVertex kBlitQuadVerts[4] = {
	{-1.0f, -1.0f, 0.0f, 1.0f},
	{-1.0f, 1.0f, 0.0f, 0.0f},
	{1.0f, -1.0f, 1.0f, 1.0f},
	{1.0f, 1.0, 1.0f, 0.0f},
	};
	GL_CALL(glGenBuffers(1, &blit_vertex_buffer_));
	GL_CALL(glBindBuffer(GL_ARRAY_BUFFER, blit_vertex_buffer_));
	GL_CALL(glBufferData(GL_ARRAY_BUFFER, sizeof(kBlitQuadVerts), kBlitQuadVerts,
	GL_STATIC_DRAW));
	}

	GraphicsContextEGL::~GraphicsContextEGL() {
	MakeCurrent();
	GL_CALL(glDeleteBuffers(1, &blit_vertex_buffer_));
	GL_CALL(glDeleteProgram(blit_program_));
	GL_CALL(glDeleteShader(blit_fragment_shader_));
	GL_CALL(glDeleteShader(blit_vertex_shader_));

	ReleaseCurrentContext();

	null_surface_ = NULL;

	EGL_CALL(eglDestroyContext(display_, context_));
	}

	void GraphicsContextEGL::MakeCurrentWithSurface(RenderTargetEGL* surface) {
	DCHECK_NE(EGL_NO_SURFACE, surface) <<
	"Use ReleaseCurrentContext().";

	EGLSurface egl_surface = surface->GetSurface();
	EGL_CALL(eglMakeCurrent(display_, egl_surface, egl_surface, context_));

	if (surface->IsWindowRenderTarget() && !surface->has_been_made_current()) {
	SecurityClear();
	}
	surface->set_has_been_made_current();

	is_current_ = true;
	current_surface_ = surface;
	}

	void GraphicsContextEGL::MakeCurrent() {
	MakeCurrentWithSurface(null_surface_);
	}

	void GraphicsContextEGL::ReleaseCurrentContext() {
	EGL_CALL(eglMakeCurrent(
	display_, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT));

	current_surface_ = NULL;
	is_current_ = false;
	}

	scoped_ptr<TextureEGL> GraphicsContextEGL::CreateTexture(
	scoped_ptr<TextureDataEGL> texture_data) {
	return make_scoped_ptr(
	new TextureEGL(this, texture_data.Pass(), bgra_format_supported_));
	}

	scoped_ptr<TextureEGL> GraphicsContextEGL::CreateTextureFromRawMemory(
	const scoped_refptr<ConstRawTextureMemoryEGL>& raw_texture_memory,
	intptr_t offset, const math::Size& size, GLenum format,
	int pitch_in_bytes) {
	const RawTextureMemoryEGL* texture_memory =
	&(raw_texture_memory->raw_texture_memory());

	return make_scoped_ptr(new TextureEGL(this, texture_memory, offset, size,
	format, pitch_in_bytes,
	bgra_format_supported_));
	}

	scoped_refptr<RenderTarget> GraphicsContextEGL::CreateOffscreenRenderTarget(
	const math::Size& dimensions) {
	scoped_refptr<RenderTarget> render_target(new PBufferRenderTargetEGL(
	display_, config_, dimensions));

	return render_target;
	}

	namespace {
	void VerticallyFlipPixels(uint8_t* pixels, int pitch_in_bytes, int height) {
	int half_height = height / 2;
	for (int row = 0; row < half_height; ++row) {
	uint8_t* top_row = pixels + row * pitch_in_bytes;
	uint8_t* bottom_row =
	pixels + (height - 1 - row) * pitch_in_bytes;
	for (int i = 0; i < pitch_in_bytes; ++i) {
	std::swap(top_row[i], bottom_row[i]);
	}
	}
	}
	} // namespace

	scoped_array<uint8_t> GraphicsContextEGL::DownloadPixelDataAsRGBA(
	const scoped_refptr<RenderTarget>& render_target) {
	TRACE_EVENT0("cobalt::renderer",
	"GraphicsContextEGL::DownloadPixelDataAsRGBA()");

	PBufferRenderTargetEGL* pbuffer_render_target =
	base::polymorphic_downcast<PBufferRenderTargetEGL*>(render_target.get());

	scoped_ptr<TextureEGL> texture(new TextureEGL(this, pbuffer_render_target));

	ScopedMakeCurrent scoped_current_context(this);

	// This shouldn't be strictly necessary as glReadPixels() should implicitly
	// call glFinish(), however it doesn't hurt to be safe and guard against
	// potentially different implementations. Performance is not an issue
	// in this function, because it is only used by tests to verify rendered
	// output.
	GL_CALL(glFinish());

	GLuint texture_framebuffer;
	GL_CALL(glGenFramebuffers(1, &texture_framebuffer));
	GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, texture_framebuffer));

	GL_CALL(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
	GL_TEXTURE_2D, texture->gl_handle(), 0));
	DCHECK_EQ(GL_FRAMEBUFFER_COMPLETE, glCheckFramebufferStatus(GL_FRAMEBUFFER));

	int pitch_in_bytes =
	texture->GetSize().width() * BytesPerPixelForGLFormat(GL_RGBA);

	scoped_array<uint8_t> pixels(
	new uint8_t[texture->GetSize().height() * pitch_in_bytes]);
	GL_CALL(glReadPixels(0, 0, texture->GetSize().width(),
	texture->GetSize().height(), GL_RGBA, GL_UNSIGNED_BYTE,
	pixels.get()));

	GL_CALL(glBindFramebuffer(GL_FRAMEBUFFER, 0));
	GL_CALL(glDeleteFramebuffers(1, &texture_framebuffer));

	// Vertically flip the resulting pixel data before returning so that the 0th
	// pixel is at the top-left. While this is not a fast procedure, this
	// entire function is only intended to be used in debug/test code.
	if (!read_pixels_needs_vertical_flip_) {
	// Lazily compute whether we need to vertically flip our read back pixels
	// or not.
	read_pixels_needs_vertical_flip_ = ComputeReadPixelsNeedVerticalFlip();
	}

	if (*read_pixels_needs_vertical_flip_) {
	// Some platforms, like the Mesa Gallium EGL implementation on Linux, seem
	// to return already flipped pixels. So in that case, we flip them again
	// before returning here.
	VerticallyFlipPixels(pixels.get(), pitch_in_bytes,
	texture->GetSize().height());
	}

	return pixels.Pass();
	}

	void GraphicsContextEGL::Blit(GLuint texture, int x, int y, int width,
	int height) {
	// Render a texture to the specified output rectangle on the render target.
	GL_CALL(glViewport(x, y, width, height));
	GL_CALL(glScissor(x, y, width, height));

	GL_CALL(glUseProgram(blit_program_));

	GL_CALL(glBindBuffer(GL_ARRAY_BUFFER, blit_vertex_buffer_));
	GL_CALL(glVertexAttribPointer(kBlitPositionAttribute, 2, GL_FLOAT, GL_FALSE,
	sizeof(float) * 4, 0));
	GL_CALL(glVertexAttribPointer(kBlitTexcoordAttribute, 2, GL_FLOAT, GL_FALSE,
	sizeof(float) * 4,
	reinterpret_cast<GLvoid>(sizeof(float) 2)));
	GL_CALL(glEnableVertexAttribArray(kBlitPositionAttribute));
	GL_CALL(glEnableVertexAttribArray(kBlitTexcoordAttribute));

	GL_CALL(glActiveTexture(GL_TEXTURE0));
	GL_CALL(glBindTexture(GL_TEXTURE_2D, texture));

	GL_CALL(glDisable(GL_BLEND));

	GL_CALL(glDrawArrays(GL_TRIANGLE_STRIP, 0, 4));

	GL_CALL(glBindTexture(GL_TEXTURE_2D, 0));

	GL_CALL(glDisableVertexAttribArray(kBlitTexcoordAttribute));
	GL_CALL(glDisableVertexAttribArray(kBlitPositionAttribute));
	GL_CALL(glUseProgram(0));
	}

	void GraphicsContextEGL::SwapBuffers(RenderTargetEGL* surface) {
	TRACE_EVENT0("cobalt::renderer", "GraphicsContextEGL::SwapBuffers()");

	EGL_CALL(eglSwapBuffers(display_, surface->GetSurface()));

	surface->increment_swap_count();
	if (surface->IsWindowRenderTarget() && surface->swap_count() <= 2) {
	SecurityClear();
	}
	}

	void GraphicsContextEGL::SecurityClear() {
	// Clear the screen to a color that is bright and gross to exaggerate that
	// this is a problem if it is witnessed.
	GL_CALL(glClearColor(1.0f, 0.4f, 1.0f, 1.0f));
	GL_CALL(glClear(GL_COLOR_BUFFER_BIT));
	}

	} // namespace backend
	} // namespace renderer
	} // namespace cobalt