content/common/gpu/media/rendering_helper.cc - platform/external/chromium_org - Git at Google

 // Copyright 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/rendering_helper.h"

 #include <algorithm>
 #include <numeric>
 #include <vector>

 #include "base/bind.h"
 #include "base/mac/scoped_nsautorelease_pool.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/stringize_macros.h"
 #include "base/synchronization/waitable_event.h"
 #include "ui/gl/gl_context.h"
 #include "ui/gl/gl_context_stub_with_extensions.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"

 #if defined(OS_WIN)
 #include <windows.h>
 #endif

 #if defined(USE_X11)
 #include "ui/gfx/x/x11_types.h"
 #endif

 #ifdef GL_VARIANT_GLX
 struct XFreeDeleter {
   void operator()(void* x) const { ::XFree(x); }
 };
 #endif

 // Helper for Shader creation.
 static void CreateShader(GLuint program,
                          GLenum type,
                          const char* source,
                          int size) {
   GLuint shader = glCreateShader(type);
   glShaderSource(shader, 1, &source, &size);
   glCompileShader(shader);
   int result = GL_FALSE;
   glGetShaderiv(shader, GL_COMPILE_STATUS, &result);
   if (!result) {
     char log[4096];
     glGetShaderInfoLog(shader, arraysize(log), NULL, log);
     LOG(FATAL) << log;
   }
   glAttachShader(program, shader);
   glDeleteShader(shader);
   CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
 }

 namespace content {

 RenderingHelperParams::RenderingHelperParams() {}

 RenderingHelperParams::~RenderingHelperParams() {}

 static const gfx::GLImplementation kGLImplementation =
 #if defined(GL_VARIANT_GLX)
     gfx::kGLImplementationDesktopGL;
 #elif defined(GL_VARIANT_EGL)
     gfx::kGLImplementationEGLGLES2;
 #else
     -1;
 #error "Unknown GL implementation."
 #endif

 RenderingHelper::RenderingHelper() {
 #if defined(GL_VARIANT_EGL)
   gl_surface_ = EGL_NO_SURFACE;
 #endif

 #if defined(OS_WIN)
   window_ = NULL;
 #else
   x_window_ = (Window)0;
 #endif

   Clear();
 }

 RenderingHelper::~RenderingHelper() {
   CHECK_EQ(clients_.size(), 0U) << "Must call UnInitialize before dtor.";
   Clear();
 }

 void RenderingHelper::Initialize(const RenderingHelperParams& params,
                                  base::WaitableEvent* done) {
   // Use cients_.size() != 0 as a proxy for the class having already been
   // Initialize()'d, and UnInitialize() before continuing.
   if (clients_.size()) {
     base::WaitableEvent done(false, false);
     UnInitialize(&done);
     done.Wait();
   }

   frame_duration_ = params.rendering_fps > 0
                         ? base::TimeDelta::FromSeconds(1) / params.rendering_fps
                         : base::TimeDelta();

   gfx::InitializeStaticGLBindings(kGLImplementation);
   scoped_refptr<gfx::GLContextStubWithExtensions> stub_context(
       new gfx::GLContextStubWithExtensions());

   render_as_thumbnails_ = params.render_as_thumbnails;
   message_loop_ = base::MessageLoop::current();

 #if GL_VARIANT_GLX
   x_display_ = gfx::GetXDisplay();
   CHECK(x_display_);
   CHECK(glXQueryVersion(x_display_, NULL, NULL));
   const int fbconfig_attr[] = {
     GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
     GLX_RENDER_TYPE, GLX_RGBA_BIT,
     GLX_BIND_TO_TEXTURE_TARGETS_EXT, GLX_TEXTURE_2D_BIT_EXT,
     GLX_BIND_TO_TEXTURE_RGB_EXT, GL_TRUE,
     GLX_DOUBLEBUFFER, True,
     GL_NONE,
   };
   int num_fbconfigs;
   scoped_ptr<GLXFBConfig, XFreeDeleter> glx_fb_configs(
       glXChooseFBConfig(x_display_, DefaultScreen(x_display_), fbconfig_attr,
                         &num_fbconfigs));
   CHECK(glx_fb_configs.get());
   CHECK_GT(num_fbconfigs, 0);
   x_visual_ = glXGetVisualFromFBConfig(x_display_, glx_fb_configs.get()[0]);
   CHECK(x_visual_);
   gl_context_ = glXCreateContext(x_display_, x_visual_, 0, true);
   CHECK(gl_context_);
   stub_context->AddExtensionsString(
       reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS)));
   stub_context->SetGLVersionString(
       reinterpret_cast<const char*>(glGetString(GL_VERSION)));

   Screen* screen = DefaultScreenOfDisplay(x_display_);
   screen_size_ = gfx::Size(XWidthOfScreen(screen), XHeightOfScreen(screen));
 #else // EGL
   EGLNativeDisplayType native_display;

 #if defined(OS_WIN)
   native_display = EGL_DEFAULT_DISPLAY;
   screen_size_ =
       gfx::Size(GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN));
 #else
   x_display_ = gfx::GetXDisplay();
   CHECK(x_display_);
   native_display = x_display_;

   Screen* screen = DefaultScreenOfDisplay(x_display_);
   screen_size_ = gfx::Size(XWidthOfScreen(screen), XHeightOfScreen(screen));
 #endif
   gl_display_ = eglGetDisplay(native_display);
   CHECK(gl_display_);
   CHECK(eglInitialize(gl_display_, NULL, NULL)) << eglGetError();

   static EGLint rgba8888[] = {
     EGL_RED_SIZE, 8,
     EGL_GREEN_SIZE, 8,
     EGL_BLUE_SIZE, 8,
     EGL_ALPHA_SIZE, 8,
     EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
     EGL_NONE,
   };
   EGLConfig egl_config;
   int num_configs;
   CHECK(eglChooseConfig(gl_display_, rgba8888, &egl_config, 1, &num_configs))
       << eglGetError();
   CHECK_GE(num_configs, 1);
   static EGLint context_attribs[] = {EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE};
   gl_context_ = eglCreateContext(
       gl_display_, egl_config, EGL_NO_CONTEXT, context_attribs);
   CHECK_NE(gl_context_, EGL_NO_CONTEXT) << eglGetError();
   stub_context->AddExtensionsString(
       reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS)));
   stub_context->AddExtensionsString(
       eglQueryString(gl_display_, EGL_EXTENSIONS));
   stub_context->SetGLVersionString(
       reinterpret_cast<const char*>(glGetString(GL_VERSION)));
 #endif
   clients_ = params.clients;
   CHECK_GT(clients_.size(), 0U);
   LayoutRenderingAreas();

 #if defined(OS_WIN)
   window_ = CreateWindowEx(0,
                            L"Static",
                            L"VideoDecodeAcceleratorTest",
                            WS_OVERLAPPEDWINDOW | WS_VISIBLE,
                            0,
                            0,
                            screen_size_.width(),
                            screen_size_.height(),
                            NULL,
                            NULL,
                            NULL,
                            NULL);
   CHECK(window_ != NULL);
 #else
   int depth = DefaultDepth(x_display_, DefaultScreen(x_display_));

 #if defined(GL_VARIANT_GLX)
   CHECK_EQ(depth, x_visual_->depth);
 #endif

   XSetWindowAttributes window_attributes;
   window_attributes.background_pixel =
       BlackPixel(x_display_, DefaultScreen(x_display_));
   window_attributes.override_redirect = true;

   x_window_ = XCreateWindow(x_display_,
                             DefaultRootWindow(x_display_),
                             0,
                             0,
                             screen_size_.width(),
                             screen_size_.height(),
                             0 /* border width */,
                             depth,
                             CopyFromParent /* class */,
                             CopyFromParent /* visual */,
                             (CWBackPixel | CWOverrideRedirect),
                             &window_attributes);
   XStoreName(x_display_, x_window_, "VideoDecodeAcceleratorTest");
   XSelectInput(x_display_, x_window_, ExposureMask);
   XMapWindow(x_display_, x_window_);
 #endif

 #if GL_VARIANT_EGL
 #if defined(OS_WIN)
   gl_surface_ =
       eglCreateWindowSurface(gl_display_, egl_config, window_, NULL);
 #else
   gl_surface_ =
       eglCreateWindowSurface(gl_display_, egl_config, x_window_, NULL);
 #endif
   CHECK_NE(gl_surface_, EGL_NO_SURFACE);
 #endif

 #if GL_VARIANT_GLX
   CHECK(glXMakeContextCurrent(x_display_, x_window_, x_window_, gl_context_));
 #else  // EGL
   CHECK(eglMakeCurrent(gl_display_, gl_surface_, gl_surface_, gl_context_))
       << eglGetError();
 #endif

   // Must be done after a context is made current.
   gfx::InitializeDynamicGLBindings(kGLImplementation, stub_context.get());

   if (render_as_thumbnails_) {
     CHECK_EQ(clients_.size(), 1U);

     GLint max_texture_size;
     glGetIntegerv(GL_MAX_TEXTURE_SIZE, &max_texture_size);
     CHECK_GE(max_texture_size, params.thumbnails_page_size.width());
     CHECK_GE(max_texture_size, params.thumbnails_page_size.height());

     thumbnails_fbo_size_ = params.thumbnails_page_size;
     thumbnail_size_ = params.thumbnail_size;

     glGenFramebuffersEXT(1, &thumbnails_fbo_id_);
     glGenTextures(1, &thumbnails_texture_id_);
     glBindTexture(GL_TEXTURE_2D, thumbnails_texture_id_);
     glTexImage2D(GL_TEXTURE_2D,
                  0,
                  GL_RGB,
                  thumbnails_fbo_size_.width(),
                  thumbnails_fbo_size_.height(),
                  0,
                  GL_RGB,
                  GL_UNSIGNED_SHORT_5_6_5,
                  NULL);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
     glBindTexture(GL_TEXTURE_2D, 0);

     glBindFramebufferEXT(GL_FRAMEBUFFER, thumbnails_fbo_id_);
     glFramebufferTexture2DEXT(GL_FRAMEBUFFER,
                               GL_COLOR_ATTACHMENT0,
                               GL_TEXTURE_2D,
                               thumbnails_texture_id_,
                               0);

     GLenum fb_status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER);
     CHECK(fb_status == GL_FRAMEBUFFER_COMPLETE) << fb_status;
     glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
     glClear(GL_COLOR_BUFFER_BIT);
     glBindFramebufferEXT(GL_FRAMEBUFFER, 0);
   }

   // These vertices and texture coords. map (0,0) in the texture to the
   // bottom left of the viewport.  Since we get the video frames with the
   // the top left at (0,0) we need to flip the texture y coordinate
   // in the vertex shader for this to be rendered the right way up.
   // In the case of thumbnail rendering we use the same vertex shader
   // to render the FBO the screen, where we do not want this flipping.
   static const float kVertices[] =
       { -1.f, 1.f, -1.f, -1.f, 1.f, 1.f, 1.f, -1.f, };
   static const float kTextureCoords[] = { 0, 1, 0, 0, 1, 1, 1, 0, };
   static const char kVertexShader[] = STRINGIZE(
       varying vec2 interp_tc;
       attribute vec4 in_pos;
       attribute vec2 in_tc;
       uniform bool tex_flip;
       void main() {
         if (tex_flip)
           interp_tc = vec2(in_tc.x, 1.0 - in_tc.y);
         else
           interp_tc = in_tc;
         gl_Position = in_pos;
       });

 #if GL_VARIANT_EGL
   static const char kFragmentShader[] =
       "#extension GL_OES_EGL_image_external : enable\n"
       "precision mediump float;\n"
       "varying vec2 interp_tc;\n"
       "uniform sampler2D tex;\n"
       "#ifdef GL_OES_EGL_image_external\n"
       "uniform samplerExternalOES tex_external;\n"
       "#endif\n"
       "void main() {\n"
       "  vec4 color = texture2D(tex, interp_tc);\n"
       "#ifdef GL_OES_EGL_image_external\n"
       "  color += texture2D(tex_external, interp_tc);\n"
       "#endif\n"
       "  gl_FragColor = color;\n"
       "}\n";
 #else
   static const char kFragmentShader[] = STRINGIZE(
       varying vec2 interp_tc;
       uniform sampler2D tex;
       void main() {
         gl_FragColor = texture2D(tex, interp_tc);
       });
 #endif
   program_ = glCreateProgram();
   CreateShader(
       program_, GL_VERTEX_SHADER, kVertexShader, arraysize(kVertexShader));
   CreateShader(program_,
                GL_FRAGMENT_SHADER,
                kFragmentShader,
                arraysize(kFragmentShader));
   glLinkProgram(program_);
   int result = GL_FALSE;
   glGetProgramiv(program_, GL_LINK_STATUS, &result);
   if (!result) {
     char log[4096];
     glGetShaderInfoLog(program_, arraysize(log), NULL, log);
     LOG(FATAL) << log;
   }
   glUseProgram(program_);
   glDeleteProgram(program_);

   glUniform1i(glGetUniformLocation(program_, "tex_flip"), 0);
   glUniform1i(glGetUniformLocation(program_, "tex"), 0);
   GLint tex_external = glGetUniformLocation(program_, "tex_external");
   if (tex_external != -1) {
     glUniform1i(tex_external, 1);
   }
   int pos_location = glGetAttribLocation(program_, "in_pos");
   glEnableVertexAttribArray(pos_location);
   glVertexAttribPointer(pos_location, 2, GL_FLOAT, GL_FALSE, 0, kVertices);
   int tc_location = glGetAttribLocation(program_, "in_tc");
   glEnableVertexAttribArray(tc_location);
   glVertexAttribPointer(tc_location, 2, GL_FLOAT, GL_FALSE, 0, kTextureCoords);

   if (frame_duration_ != base::TimeDelta()) {
     render_timer_.reset(new base::RepeatingTimer<RenderingHelper>());
     render_timer_->Start(
         FROM_HERE, frame_duration_, this, &RenderingHelper::RenderContent);
   }
   done->Signal();
 }

 void RenderingHelper::UnInitialize(base::WaitableEvent* done) {
   CHECK_EQ(base::MessageLoop::current(), message_loop_);

   // Deletion will also stop the timer.
   render_timer_.reset();

   if (render_as_thumbnails_) {
     glDeleteTextures(1, &thumbnails_texture_id_);
     glDeleteFramebuffersEXT(1, &thumbnails_fbo_id_);
   }
 #if GL_VARIANT_GLX

   glXDestroyContext(x_display_, gl_context_);
 #else // EGL
   CHECK(eglMakeCurrent(
       gl_display_, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT))
       << eglGetError();
   CHECK(eglDestroyContext(gl_display_, gl_context_));
   CHECK(eglDestroySurface(gl_display_, gl_surface_));
   CHECK(eglTerminate(gl_display_));
 #endif
   gfx::ClearGLBindings();
   Clear();
   done->Signal();
 }

 void RenderingHelper::CreateTexture(uint32 texture_target,
                                     uint32* texture_id,
                                     const gfx::Size& size,
                                     base::WaitableEvent* done) {
   if (base::MessageLoop::current() != message_loop_) {
     message_loop_->PostTask(FROM_HERE,
                             base::Bind(&RenderingHelper::CreateTexture,
                                        base::Unretained(this),
                                        texture_target,
                                        texture_id,
                                        size,
                                        done));
     return;
   }
   glGenTextures(1, texture_id);
   glBindTexture(texture_target, *texture_id);
   if (texture_target == GL_TEXTURE_2D) {
     glTexImage2D(GL_TEXTURE_2D,
                  0,
                  GL_RGBA,
                  size.width(),
                  size.height(),
                  0,
                  GL_RGBA,
                  GL_UNSIGNED_BYTE,
                  NULL);
   }
   glTexParameteri(texture_target, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
   glTexParameteri(texture_target, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
   // OpenGLES2.0.25 section 3.8.2 requires CLAMP_TO_EDGE for NPOT textures.
   glTexParameteri(texture_target, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
   glTexParameteri(texture_target, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
   CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
   done->Signal();
 }

 // Helper function to set GL viewport.
 static inline void GLSetViewPort(const gfx::Rect& area) {
   glViewport(area.x(), area.y(), area.width(), area.height());
   glScissor(area.x(), area.y(), area.width(), area.height());
 }

 void RenderingHelper::RenderThumbnail(uint32 texture_target,
                                       uint32 texture_id) {
   CHECK_EQ(base::MessageLoop::current(), message_loop_);
   const int width = thumbnail_size_.width();
   const int height = thumbnail_size_.height();
   const int thumbnails_in_row = thumbnails_fbo_size_.width() / width;
   const int thumbnails_in_column = thumbnails_fbo_size_.height() / height;
   const int row = (frame_count_ / thumbnails_in_row) % thumbnails_in_column;
   const int col = frame_count_ % thumbnails_in_row;

   gfx::Rect area(col * width, row * height, width, height);

   glUniform1i(glGetUniformLocation(program_, "tex_flip"), 0);
   glBindFramebufferEXT(GL_FRAMEBUFFER, thumbnails_fbo_id_);
   GLSetViewPort(area);
   RenderTexture(texture_target, texture_id);
   glBindFramebufferEXT(GL_FRAMEBUFFER, 0);
   ++frame_count_;
 }

 void RenderingHelper::RenderTexture(uint32 texture_target, uint32 texture_id) {
   // The ExternalOES sampler is bound to GL_TEXTURE1 and the Texture2D sampler
   // is bound to GL_TEXTURE0.
   if (texture_target == GL_TEXTURE_2D) {
     glActiveTexture(GL_TEXTURE0 + 0);
   } else if (texture_target == GL_TEXTURE_EXTERNAL_OES) {
     glActiveTexture(GL_TEXTURE0 + 1);
   }
   glBindTexture(texture_target, texture_id);
   glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
   glBindTexture(texture_target, 0);
   CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
 }

 void RenderingHelper::DeleteTexture(uint32 texture_id) {
   glDeleteTextures(1, &texture_id);
   CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
 }

 NativeContextType RenderingHelper::GetGLContext() { return gl_context_; }

 void* RenderingHelper::GetGLDisplay() {
 #if GL_VARIANT_GLX
   return x_display_;
 #else  // EGL
   return gl_display_;
 #endif
 }

 void RenderingHelper::Clear() {
   clients_.clear();
   message_loop_ = NULL;
   gl_context_ = NULL;
 #if GL_VARIANT_EGL
   gl_display_ = EGL_NO_DISPLAY;
   gl_surface_ = EGL_NO_SURFACE;
 #endif
   render_as_thumbnails_ = false;
   frame_count_ = 0;
   thumbnails_fbo_id_ = 0;
   thumbnails_texture_id_ = 0;

 #if defined(OS_WIN)
   if (window_) {
     DestroyWindow(window_);
     window_ = NULL;
   }
 #else
   // Destroy resources acquired in Initialize, in reverse-acquisition order.
   if (x_window_) {
     CHECK(XUnmapWindow(x_display_, x_window_));
     CHECK(XDestroyWindow(x_display_, x_window_));
     x_window_ = (Window)0;
   }
   // Mimic newly created object.
   x_display_ = NULL;
 #endif
 }

 void RenderingHelper::GetThumbnailsAsRGB(std::vector<unsigned char>* rgb,
                                          bool* alpha_solid,
                                          base::WaitableEvent* done) {
   CHECK(render_as_thumbnails_);

   const size_t num_pixels = thumbnails_fbo_size_.GetArea();
   std::vector<unsigned char> rgba;
   rgba.resize(num_pixels * 4);
   glBindFramebufferEXT(GL_FRAMEBUFFER, thumbnails_fbo_id_);
   glPixelStorei(GL_PACK_ALIGNMENT, 1);
   // We can only count on GL_RGBA/GL_UNSIGNED_BYTE support.
   glReadPixels(0,
                0,
                thumbnails_fbo_size_.width(),
                thumbnails_fbo_size_.height(),
                GL_RGBA,
                GL_UNSIGNED_BYTE,
                &rgba[0]);
   glBindFramebufferEXT(GL_FRAMEBUFFER, 0);
   rgb->resize(num_pixels * 3);
   // Drop the alpha channel, but check as we go that it is all 0xff.
   bool solid = true;
   unsigned char* rgb_ptr = &((*rgb)[0]);
   unsigned char* rgba_ptr = &rgba[0];
   for (size_t i = 0; i < num_pixels; ++i) {
     *rgb_ptr++ = *rgba_ptr++;
     *rgb_ptr++ = *rgba_ptr++;
     *rgb_ptr++ = *rgba_ptr++;
     solid = solid && (*rgba_ptr == 0xff);
     rgba_ptr++;
   }
   *alpha_solid = solid;

   done->Signal();
 }

 void RenderingHelper::RenderContent() {
   CHECK_EQ(base::MessageLoop::current(), message_loop_);
   glUniform1i(glGetUniformLocation(program_, "tex_flip"), 1);

   if (render_as_thumbnails_) {
     // In render_as_thumbnails_ mode, we render the FBO content on the
     // screen instead of the decoded textures.
     GLSetViewPort(render_areas_[0]);
     RenderTexture(GL_TEXTURE_2D, thumbnails_texture_id_);
   } else {
     for (size_t i = 0; i < clients_.size(); ++i) {
       if (clients_[i]) {
         GLSetViewPort(render_areas_[i]);
         clients_[i]->RenderContent(this);
       }
     }
   }

 #if GL_VARIANT_GLX
   glXSwapBuffers(x_display_, x_window_);
 #else  // EGL
   eglSwapBuffers(gl_display_, gl_surface_);
   CHECK_EQ(static_cast<int>(eglGetError()), EGL_SUCCESS);
 #endif
 }

 // Helper function for the LayoutRenderingAreas(). The |lengths| are the
 // heights(widths) of the rows(columns). It scales the elements in
 // |lengths| proportionally so that the sum of them equal to |total_length|.
 // It also outputs the coordinates of the rows(columns) to |offsets|.
 static void ScaleAndCalculateOffsets(std::vector<int>* lengths,
                                      std::vector<int>* offsets,
                                      int total_length) {
   int sum = std::accumulate(lengths->begin(), lengths->end(), 0);
   for (size_t i = 0; i < lengths->size(); ++i) {
     lengths->at(i) = lengths->at(i) * total_length / sum;
     offsets->at(i) = (i == 0) ? 0 : offsets->at(i - 1) + lengths->at(i - 1);
   }
 }

 void RenderingHelper::LayoutRenderingAreas() {
   // Find the number of colums and rows.
   // The smallest n * n or n * (n + 1) > number of clients.
   size_t cols = sqrt(clients_.size() - 1) + 1;
   size_t rows = (clients_.size() + cols - 1) / cols;

   // Find the widths and heights of the grid.
   std::vector<int> widths(cols);
   std::vector<int> heights(rows);
   std::vector<int> offset_x(cols);
   std::vector<int> offset_y(rows);

   for (size_t i = 0; i < clients_.size(); ++i) {
     const gfx::Size& window_size = clients_[i]->GetWindowSize();
     widths[i % cols] = std::max(widths[i % cols], window_size.width());
     heights[i / cols] = std::max(heights[i / cols], window_size.height());
   }

   ScaleAndCalculateOffsets(&widths, &offset_x, screen_size_.width());
   ScaleAndCalculateOffsets(&heights, &offset_y, screen_size_.height());

   // Put each render_area_ in the center of each cell.
   render_areas_.clear();
   for (size_t i = 0; i < clients_.size(); ++i) {
     const gfx::Size& window_size = clients_[i]->GetWindowSize();
     float scale =
         std::min(static_cast<float>(widths[i % cols]) / window_size.width(),
                  static_cast<float>(heights[i / cols]) / window_size.height());

     // Don't scale up the texture.
     scale = std::min(1.0f, scale);

     size_t w = scale * window_size.width();
     size_t h = scale * window_size.height();
     size_t x = offset_x[i % cols] + (widths[i % cols] - w) / 2;
     size_t y = offset_y[i / cols] + (heights[i / cols] - h) / 2;
     render_areas_.push_back(gfx::Rect(x, y, w, h));
   }
 }
 }  // namespace content
	// Copyright 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/rendering_helper.h"

	#include <algorithm>
	#include <numeric>
	#include <vector>

	#include "base/bind.h"
	#include "base/mac/scoped_nsautorelease_pool.h"
	#include "base/message_loop/message_loop.h"
	#include "base/strings/stringize_macros.h"
	#include "base/synchronization/waitable_event.h"
	#include "ui/gl/gl_context.h"
	#include "ui/gl/gl_context_stub_with_extensions.h"
	#include "ui/gl/gl_implementation.h"
	#include "ui/gl/gl_surface.h"

	#if defined(OS_WIN)
	#include <windows.h>
	#endif

	#if defined(USE_X11)
	#include "ui/gfx/x/x11_types.h"
	#endif

	#ifdef GL_VARIANT_GLX
	struct XFreeDeleter {
	void operator()(void* x) const { ::XFree(x); }
	};
	#endif

	// Helper for Shader creation.
	static void CreateShader(GLuint program,
	GLenum type,
	const char* source,
	int size) {
	GLuint shader = glCreateShader(type);
	glShaderSource(shader, 1, &source, &size);
	glCompileShader(shader);
	int result = GL_FALSE;
	glGetShaderiv(shader, GL_COMPILE_STATUS, &result);
	if (!result) {
	char log[4096];
	glGetShaderInfoLog(shader, arraysize(log), NULL, log);
	LOG(FATAL) << log;
	}
	glAttachShader(program, shader);
	glDeleteShader(shader);
	CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
	}

	namespace content {

	RenderingHelperParams::RenderingHelperParams() {}

	RenderingHelperParams::~RenderingHelperParams() {}

	static const gfx::GLImplementation kGLImplementation =
	#if defined(GL_VARIANT_GLX)
	gfx::kGLImplementationDesktopGL;
	#elif defined(GL_VARIANT_EGL)
	gfx::kGLImplementationEGLGLES2;
	#else
	-1;
	#error "Unknown GL implementation."
	#endif

	RenderingHelper::RenderingHelper() {
	#if defined(GL_VARIANT_EGL)
	gl_surface_ = EGL_NO_SURFACE;
	#endif

	#if defined(OS_WIN)
	window_ = NULL;
	#else
	x_window_ = (Window)0;
	#endif

	Clear();
	}

	RenderingHelper::~RenderingHelper() {
	CHECK_EQ(clients_.size(), 0U) << "Must call UnInitialize before dtor.";
	Clear();
	}

	void RenderingHelper::Initialize(const RenderingHelperParams& params,
	base::WaitableEvent* done) {
	// Use cients_.size() != 0 as a proxy for the class having already been
	// Initialize()'d, and UnInitialize() before continuing.
	if (clients_.size()) {
	base::WaitableEvent done(false, false);
	UnInitialize(&done);
	done.Wait();
	}

	frame_duration_ = params.rendering_fps > 0
	? base::TimeDelta::FromSeconds(1) / params.rendering_fps
	: base::TimeDelta();

	gfx::InitializeStaticGLBindings(kGLImplementation);
	scoped_refptr<gfx::GLContextStubWithExtensions> stub_context(
	new gfx::GLContextStubWithExtensions());

	render_as_thumbnails_ = params.render_as_thumbnails;
	message_loop_ = base::MessageLoop::current();

	#if GL_VARIANT_GLX
	x_display_ = gfx::GetXDisplay();
	CHECK(x_display_);
	CHECK(glXQueryVersion(x_display_, NULL, NULL));
	const int fbconfig_attr[] = {
	GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
	GLX_RENDER_TYPE, GLX_RGBA_BIT,
	GLX_BIND_TO_TEXTURE_TARGETS_EXT, GLX_TEXTURE_2D_BIT_EXT,
	GLX_BIND_TO_TEXTURE_RGB_EXT, GL_TRUE,
	GLX_DOUBLEBUFFER, True,
	GL_NONE,
	};
	int num_fbconfigs;
	scoped_ptr<GLXFBConfig, XFreeDeleter> glx_fb_configs(
	glXChooseFBConfig(x_display_, DefaultScreen(x_display_), fbconfig_attr,
	&num_fbconfigs));
	CHECK(glx_fb_configs.get());
	CHECK_GT(num_fbconfigs, 0);
	x_visual_ = glXGetVisualFromFBConfig(x_display_, glx_fb_configs.get()[0]);
	CHECK(x_visual_);
	gl_context_ = glXCreateContext(x_display_, x_visual_, 0, true);
	CHECK(gl_context_);
	stub_context->AddExtensionsString(
	reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS)));
	stub_context->SetGLVersionString(
	reinterpret_cast<const char*>(glGetString(GL_VERSION)));

	Screen* screen = DefaultScreenOfDisplay(x_display_);
	screen_size_ = gfx::Size(XWidthOfScreen(screen), XHeightOfScreen(screen));
	#else // EGL
	EGLNativeDisplayType native_display;

	#if defined(OS_WIN)
	native_display = EGL_DEFAULT_DISPLAY;
	screen_size_ =
	gfx::Size(GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN));
	#else
	x_display_ = gfx::GetXDisplay();
	CHECK(x_display_);
	native_display = x_display_;

	Screen* screen = DefaultScreenOfDisplay(x_display_);
	screen_size_ = gfx::Size(XWidthOfScreen(screen), XHeightOfScreen(screen));
	#endif
	gl_display_ = eglGetDisplay(native_display);
	CHECK(gl_display_);
	CHECK(eglInitialize(gl_display_, NULL, NULL)) << eglGetError();

	static EGLint rgba8888[] = {
	EGL_RED_SIZE, 8,
	EGL_GREEN_SIZE, 8,
	EGL_BLUE_SIZE, 8,
	EGL_ALPHA_SIZE, 8,
	EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
	EGL_NONE,
	};
	EGLConfig egl_config;
	int num_configs;
	CHECK(eglChooseConfig(gl_display_, rgba8888, &egl_config, 1, &num_configs))
	<< eglGetError();
	CHECK_GE(num_configs, 1);
	static EGLint context_attribs[] = {EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE};
	gl_context_ = eglCreateContext(
	gl_display_, egl_config, EGL_NO_CONTEXT, context_attribs);
	CHECK_NE(gl_context_, EGL_NO_CONTEXT) << eglGetError();
	stub_context->AddExtensionsString(
	reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS)));
	stub_context->AddExtensionsString(
	eglQueryString(gl_display_, EGL_EXTENSIONS));
	stub_context->SetGLVersionString(
	reinterpret_cast<const char*>(glGetString(GL_VERSION)));
	#endif
	clients_ = params.clients;
	CHECK_GT(clients_.size(), 0U);
	LayoutRenderingAreas();

	#if defined(OS_WIN)
	window_ = CreateWindowEx(0,
	L"Static",
	L"VideoDecodeAcceleratorTest",
	WS_OVERLAPPEDWINDOW \| WS_VISIBLE,
	0,
	0,
	screen_size_.width(),
	screen_size_.height(),
	NULL,
	NULL,
	NULL,
	NULL);
	CHECK(window_ != NULL);
	#else
	int depth = DefaultDepth(x_display_, DefaultScreen(x_display_));

	#if defined(GL_VARIANT_GLX)
	CHECK_EQ(depth, x_visual_->depth);
	#endif

	XSetWindowAttributes window_attributes;
	window_attributes.background_pixel =
	BlackPixel(x_display_, DefaultScreen(x_display_));
	window_attributes.override_redirect = true;

	x_window_ = XCreateWindow(x_display_,
	DefaultRootWindow(x_display_),
	0,
	0,
	screen_size_.width(),
	screen_size_.height(),
	0 /* border width */,
	depth,
	CopyFromParent /* class */,
	CopyFromParent /* visual */,
	(CWBackPixel \| CWOverrideRedirect),
	&window_attributes);
	XStoreName(x_display_, x_window_, "VideoDecodeAcceleratorTest");
	XSelectInput(x_display_, x_window_, ExposureMask);
	XMapWindow(x_display_, x_window_);
	#endif

	#if GL_VARIANT_EGL
	#if defined(OS_WIN)
	gl_surface_ =
	eglCreateWindowSurface(gl_display_, egl_config, window_, NULL);
	#else
	gl_surface_ =
	eglCreateWindowSurface(gl_display_, egl_config, x_window_, NULL);
	#endif
	CHECK_NE(gl_surface_, EGL_NO_SURFACE);
	#endif

	#if GL_VARIANT_GLX
	CHECK(glXMakeContextCurrent(x_display_, x_window_, x_window_, gl_context_));
	#else // EGL
	CHECK(eglMakeCurrent(gl_display_, gl_surface_, gl_surface_, gl_context_))
	<< eglGetError();
	#endif

	// Must be done after a context is made current.
	gfx::InitializeDynamicGLBindings(kGLImplementation, stub_context.get());

	if (render_as_thumbnails_) {
	CHECK_EQ(clients_.size(), 1U);

	GLint max_texture_size;
	glGetIntegerv(GL_MAX_TEXTURE_SIZE, &max_texture_size);
	CHECK_GE(max_texture_size, params.thumbnails_page_size.width());
	CHECK_GE(max_texture_size, params.thumbnails_page_size.height());

	thumbnails_fbo_size_ = params.thumbnails_page_size;
	thumbnail_size_ = params.thumbnail_size;

	glGenFramebuffersEXT(1, &thumbnails_fbo_id_);
	glGenTextures(1, &thumbnails_texture_id_);
	glBindTexture(GL_TEXTURE_2D, thumbnails_texture_id_);
	glTexImage2D(GL_TEXTURE_2D,
	0,
	GL_RGB,
	thumbnails_fbo_size_.width(),
	thumbnails_fbo_size_.height(),
	0,
	GL_RGB,
	GL_UNSIGNED_SHORT_5_6_5,
	NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glBindTexture(GL_TEXTURE_2D, 0);

	glBindFramebufferEXT(GL_FRAMEBUFFER, thumbnails_fbo_id_);
	glFramebufferTexture2DEXT(GL_FRAMEBUFFER,
	GL_COLOR_ATTACHMENT0,
	GL_TEXTURE_2D,
	thumbnails_texture_id_,
	0);

	GLenum fb_status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER);
	CHECK(fb_status == GL_FRAMEBUFFER_COMPLETE) << fb_status;
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
	glClear(GL_COLOR_BUFFER_BIT);
	glBindFramebufferEXT(GL_FRAMEBUFFER, 0);
	}

	// These vertices and texture coords. map (0,0) in the texture to the
	// bottom left of the viewport. Since we get the video frames with the
	// the top left at (0,0) we need to flip the texture y coordinate
	// in the vertex shader for this to be rendered the right way up.
	// In the case of thumbnail rendering we use the same vertex shader
	// to render the FBO the screen, where we do not want this flipping.
	static const float kVertices[] =
	{ -1.f, 1.f, -1.f, -1.f, 1.f, 1.f, 1.f, -1.f, };
	static const float kTextureCoords[] = { 0, 1, 0, 0, 1, 1, 1, 0, };
	static const char kVertexShader[] = STRINGIZE(
	varying vec2 interp_tc;
	attribute vec4 in_pos;
	attribute vec2 in_tc;
	uniform bool tex_flip;
	void main() {
	if (tex_flip)
	interp_tc = vec2(in_tc.x, 1.0 - in_tc.y);
	else
	interp_tc = in_tc;
	gl_Position = in_pos;
	});

	#if GL_VARIANT_EGL
	static const char kFragmentShader[] =
	"#extension GL_OES_EGL_image_external : enable\n"
	"precision mediump float;\n"
	"varying vec2 interp_tc;\n"
	"uniform sampler2D tex;\n"
	"#ifdef GL_OES_EGL_image_external\n"
	"uniform samplerExternalOES tex_external;\n"
	"#endif\n"
	"void main() {\n"
	" vec4 color = texture2D(tex, interp_tc);\n"
	"#ifdef GL_OES_EGL_image_external\n"
	" color += texture2D(tex_external, interp_tc);\n"
	"#endif\n"
	" gl_FragColor = color;\n"
	"}\n";
	#else
	static const char kFragmentShader[] = STRINGIZE(
	varying vec2 interp_tc;
	uniform sampler2D tex;
	void main() {
	gl_FragColor = texture2D(tex, interp_tc);
	});
	#endif
	program_ = glCreateProgram();
	CreateShader(
	program_, GL_VERTEX_SHADER, kVertexShader, arraysize(kVertexShader));
	CreateShader(program_,
	GL_FRAGMENT_SHADER,
	kFragmentShader,
	arraysize(kFragmentShader));
	glLinkProgram(program_);
	int result = GL_FALSE;
	glGetProgramiv(program_, GL_LINK_STATUS, &result);
	if (!result) {
	char log[4096];
	glGetShaderInfoLog(program_, arraysize(log), NULL, log);
	LOG(FATAL) << log;
	}
	glUseProgram(program_);
	glDeleteProgram(program_);

	glUniform1i(glGetUniformLocation(program_, "tex_flip"), 0);
	glUniform1i(glGetUniformLocation(program_, "tex"), 0);
	GLint tex_external = glGetUniformLocation(program_, "tex_external");
	if (tex_external != -1) {
	glUniform1i(tex_external, 1);
	}
	int pos_location = glGetAttribLocation(program_, "in_pos");
	glEnableVertexAttribArray(pos_location);
	glVertexAttribPointer(pos_location, 2, GL_FLOAT, GL_FALSE, 0, kVertices);
	int tc_location = glGetAttribLocation(program_, "in_tc");
	glEnableVertexAttribArray(tc_location);
	glVertexAttribPointer(tc_location, 2, GL_FLOAT, GL_FALSE, 0, kTextureCoords);

	if (frame_duration_ != base::TimeDelta()) {
	render_timer_.reset(new base::RepeatingTimer<RenderingHelper>());
	render_timer_->Start(
	FROM_HERE, frame_duration_, this, &RenderingHelper::RenderContent);
	}
	done->Signal();
	}

	void RenderingHelper::UnInitialize(base::WaitableEvent* done) {
	CHECK_EQ(base::MessageLoop::current(), message_loop_);

	// Deletion will also stop the timer.
	render_timer_.reset();

	if (render_as_thumbnails_) {
	glDeleteTextures(1, &thumbnails_texture_id_);
	glDeleteFramebuffersEXT(1, &thumbnails_fbo_id_);
	}
	#if GL_VARIANT_GLX

	glXDestroyContext(x_display_, gl_context_);
	#else // EGL
	CHECK(eglMakeCurrent(
	gl_display_, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT))
	<< eglGetError();
	CHECK(eglDestroyContext(gl_display_, gl_context_));
	CHECK(eglDestroySurface(gl_display_, gl_surface_));
	CHECK(eglTerminate(gl_display_));
	#endif
	gfx::ClearGLBindings();
	Clear();
	done->Signal();
	}

	void RenderingHelper::CreateTexture(uint32 texture_target,
	uint32* texture_id,
	const gfx::Size& size,
	base::WaitableEvent* done) {
	if (base::MessageLoop::current() != message_loop_) {
	message_loop_->PostTask(FROM_HERE,
	base::Bind(&RenderingHelper::CreateTexture,
	base::Unretained(this),
	texture_target,
	texture_id,
	size,
	done));
	return;
	}
	glGenTextures(1, texture_id);
	glBindTexture(texture_target, *texture_id);
	if (texture_target == GL_TEXTURE_2D) {
	glTexImage2D(GL_TEXTURE_2D,
	0,
	GL_RGBA,
	size.width(),
	size.height(),
	0,
	GL_RGBA,
	GL_UNSIGNED_BYTE,
	NULL);
	}
	glTexParameteri(texture_target, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(texture_target, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	// OpenGLES2.0.25 section 3.8.2 requires CLAMP_TO_EDGE for NPOT textures.
	glTexParameteri(texture_target, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(texture_target, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
	CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
	done->Signal();
	}

	// Helper function to set GL viewport.
	static inline void GLSetViewPort(const gfx::Rect& area) {
	glViewport(area.x(), area.y(), area.width(), area.height());
	glScissor(area.x(), area.y(), area.width(), area.height());
	}

	void RenderingHelper::RenderThumbnail(uint32 texture_target,
	uint32 texture_id) {
	CHECK_EQ(base::MessageLoop::current(), message_loop_);
	const int width = thumbnail_size_.width();
	const int height = thumbnail_size_.height();
	const int thumbnails_in_row = thumbnails_fbo_size_.width() / width;
	const int thumbnails_in_column = thumbnails_fbo_size_.height() / height;
	const int row = (frame_count_ / thumbnails_in_row) % thumbnails_in_column;
	const int col = frame_count_ % thumbnails_in_row;

	gfx::Rect area(col * width, row * height, width, height);

	glUniform1i(glGetUniformLocation(program_, "tex_flip"), 0);
	glBindFramebufferEXT(GL_FRAMEBUFFER, thumbnails_fbo_id_);
	GLSetViewPort(area);
	RenderTexture(texture_target, texture_id);
	glBindFramebufferEXT(GL_FRAMEBUFFER, 0);
	++frame_count_;
	}

	void RenderingHelper::RenderTexture(uint32 texture_target, uint32 texture_id) {
	// The ExternalOES sampler is bound to GL_TEXTURE1 and the Texture2D sampler
	// is bound to GL_TEXTURE0.
	if (texture_target == GL_TEXTURE_2D) {
	glActiveTexture(GL_TEXTURE0 + 0);
	} else if (texture_target == GL_TEXTURE_EXTERNAL_OES) {
	glActiveTexture(GL_TEXTURE0 + 1);
	}
	glBindTexture(texture_target, texture_id);
	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
	glBindTexture(texture_target, 0);
	CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
	}

	void RenderingHelper::DeleteTexture(uint32 texture_id) {
	glDeleteTextures(1, &texture_id);
	CHECK_EQ(static_cast<int>(glGetError()), GL_NO_ERROR);
	}

	NativeContextType RenderingHelper::GetGLContext() { return gl_context_; }

	void* RenderingHelper::GetGLDisplay() {
	#if GL_VARIANT_GLX
	return x_display_;
	#else // EGL
	return gl_display_;
	#endif
	}

	void RenderingHelper::Clear() {
	clients_.clear();
	message_loop_ = NULL;
	gl_context_ = NULL;
	#if GL_VARIANT_EGL
	gl_display_ = EGL_NO_DISPLAY;
	gl_surface_ = EGL_NO_SURFACE;
	#endif
	render_as_thumbnails_ = false;
	frame_count_ = 0;
	thumbnails_fbo_id_ = 0;
	thumbnails_texture_id_ = 0;

	#if defined(OS_WIN)
	if (window_) {
	DestroyWindow(window_);
	window_ = NULL;
	}
	#else
	// Destroy resources acquired in Initialize, in reverse-acquisition order.
	if (x_window_) {
	CHECK(XUnmapWindow(x_display_, x_window_));
	CHECK(XDestroyWindow(x_display_, x_window_));
	x_window_ = (Window)0;
	}
	// Mimic newly created object.
	x_display_ = NULL;
	#endif
	}

	void RenderingHelper::GetThumbnailsAsRGB(std::vector<unsigned char>* rgb,
	bool* alpha_solid,
	base::WaitableEvent* done) {
	CHECK(render_as_thumbnails_);

	const size_t num_pixels = thumbnails_fbo_size_.GetArea();
	std::vector<unsigned char> rgba;
	rgba.resize(num_pixels * 4);
	glBindFramebufferEXT(GL_FRAMEBUFFER, thumbnails_fbo_id_);
	glPixelStorei(GL_PACK_ALIGNMENT, 1);
	// We can only count on GL_RGBA/GL_UNSIGNED_BYTE support.
	glReadPixels(0,
	0,
	thumbnails_fbo_size_.width(),
	thumbnails_fbo_size_.height(),
	GL_RGBA,
	GL_UNSIGNED_BYTE,
	&rgba[0]);
	glBindFramebufferEXT(GL_FRAMEBUFFER, 0);
	rgb->resize(num_pixels * 3);
	// Drop the alpha channel, but check as we go that it is all 0xff.
	bool solid = true;
	unsigned char* rgb_ptr = &((*rgb)[0]);
	unsigned char* rgba_ptr = &rgba[0];
	for (size_t i = 0; i < num_pixels; ++i) {
	rgb_ptr++ = rgba_ptr++;
	rgb_ptr++ = rgba_ptr++;
	rgb_ptr++ = rgba_ptr++;
	solid = solid && (*rgba_ptr == 0xff);
	rgba_ptr++;
	}
	*alpha_solid = solid;

	done->Signal();
	}

	void RenderingHelper::RenderContent() {
	CHECK_EQ(base::MessageLoop::current(), message_loop_);
	glUniform1i(glGetUniformLocation(program_, "tex_flip"), 1);

	if (render_as_thumbnails_) {
	// In render_as_thumbnails_ mode, we render the FBO content on the
	// screen instead of the decoded textures.
	GLSetViewPort(render_areas_[0]);
	RenderTexture(GL_TEXTURE_2D, thumbnails_texture_id_);
	} else {
	for (size_t i = 0; i < clients_.size(); ++i) {
	if (clients_[i]) {
	GLSetViewPort(render_areas_[i]);
	clients_[i]->RenderContent(this);
	}
	}
	}

	#if GL_VARIANT_GLX
	glXSwapBuffers(x_display_, x_window_);
	#else // EGL
	eglSwapBuffers(gl_display_, gl_surface_);
	CHECK_EQ(static_cast<int>(eglGetError()), EGL_SUCCESS);
	#endif
	}

	// Helper function for the LayoutRenderingAreas(). The \|lengths\| are the
	// heights(widths) of the rows(columns). It scales the elements in
	// \|lengths\| proportionally so that the sum of them equal to \|total_length\|.
	// It also outputs the coordinates of the rows(columns) to \|offsets\|.
	static void ScaleAndCalculateOffsets(std::vector<int>* lengths,
	std::vector<int>* offsets,
	int total_length) {
	int sum = std::accumulate(lengths->begin(), lengths->end(), 0);
	for (size_t i = 0; i < lengths->size(); ++i) {
	lengths->at(i) = lengths->at(i) * total_length / sum;
	offsets->at(i) = (i == 0) ? 0 : offsets->at(i - 1) + lengths->at(i - 1);
	}
	}

	void RenderingHelper::LayoutRenderingAreas() {
	// Find the number of colums and rows.
	// The smallest n * n or n * (n + 1) > number of clients.
	size_t cols = sqrt(clients_.size() - 1) + 1;
	size_t rows = (clients_.size() + cols - 1) / cols;

	// Find the widths and heights of the grid.
	std::vector<int> widths(cols);
	std::vector<int> heights(rows);
	std::vector<int> offset_x(cols);
	std::vector<int> offset_y(rows);

	for (size_t i = 0; i < clients_.size(); ++i) {
	const gfx::Size& window_size = clients_[i]->GetWindowSize();
	widths[i % cols] = std::max(widths[i % cols], window_size.width());
	heights[i / cols] = std::max(heights[i / cols], window_size.height());
	}

	ScaleAndCalculateOffsets(&widths, &offset_x, screen_size_.width());
	ScaleAndCalculateOffsets(&heights, &offset_y, screen_size_.height());

	// Put each render_area_ in the center of each cell.
	render_areas_.clear();
	for (size_t i = 0; i < clients_.size(); ++i) {
	const gfx::Size& window_size = clients_[i]->GetWindowSize();
	float scale =
	std::min(static_cast<float>(widths[i % cols]) / window_size.width(),
	static_cast<float>(heights[i / cols]) / window_size.height());

	// Don't scale up the texture.
	scale = std::min(1.0f, scale);

	size_t w = scale * window_size.width();
	size_t h = scale * window_size.height();
	size_t x = offset_x[i % cols] + (widths[i % cols] - w) / 2;
	size_t y = offset_y[i / cols] + (heights[i / cols] - h) / 2;
	render_areas_.push_back(gfx::Rect(x, y, w, h));
	}
	}
	} // namespace content