emulate srgb format for generateMipmap

gpu/command_buffer/service/gles2_cmd_srgb_converter.cc

+// Copyright (c) 2016 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 "gpu/command_buffer/service/gles2_cmd_srgb_converter.h"
+
+#include "gpu/command_buffer/service/texture_manager.h"
+#include "ui/gl/gl_version_info.h"
+
+namespace {
+
+void CompileShader(GLuint shader, const char* shader_source) {
+  glShaderSource(shader, 1, &shader_source, 0);
+  glCompileShader(shader);
+#ifndef NDEBUG
+  GLint compile_status;
+  glGetShaderiv(shader, GL_COMPILE_STATUS, &compile_status);
+  if (GL_TRUE != compile_status)
+    DLOG(ERROR) << "CopyTexImage: shader compilation failure.";
+#endif
+}
+
+}  // anonymous namespace
+
+namespace gpu {
+namespace gles2 {
+
+SRGBConverter::SRGBConverter(const gles2::FeatureInfo* feature_info)
+    : feature_info_(feature_info) {}
+
+SRGBConverter::~SRGBConverter() {}
+
+// Vertex shader, shared by both decoder program and encoder program
+static const char* vs_source =
+    "#version 150\n"
+    "out vec2 v_texcoord;\n"
+    "\n"
+    "void main()\n"
+    "{\n"
+    "    const vec2 quad_positions[6] = vec2[6]\n"
+    "    (\n"
+    "        vec2(0.0f, 0.0f),\n"
+    "        vec2(0.0f, 1.0f),\n"
+    "        vec2(1.0f, 0.0f),\n"
+    "\n"
+    "        vec2(0.0f, 1.0f),\n"
+    "        vec2(1.0f, 0.0f),\n"
+    "        vec2(1.0f, 1.0f)\n"
+    "    );\n"
+    "\n"
+    "    vec2 xy = vec2((quad_positions[gl_VertexID] * 2.0) - 1.0);\n"
+    "    gl_Position = vec4(xy, 0.0, 1.0);\n"
+    "    v_texcoord = quad_positions[gl_VertexID];\n"
+    "}\n";
+
+void SRGBConverter::InitializeSRGBDecoder(const gles2::GLES2Decoder* decoder) {
+  if (srgb_decoder_initialized_) {
+    return;
+  }
+
+  srgb_decoder_program_ = glCreateProgram();
+
+  // Compile the vertex shader
+  GLuint vs = glCreateShader(GL_VERTEX_SHADER);
+  CompileShader(vs, vs_source);
+  glAttachShader(srgb_decoder_program_, vs);
+  glDeleteShader(vs);
+
+  // Compile the fragment shader
+
+  // Sampling texels from a srgb texture to a linear image, it will convert
+  // the srgb color space to linear color space automatically as a part of
+  // filtering. See the section <sRGB Texture Color Conversion> in GLES and
+  // OpenGL spec. So in decoder, we don't need to decode again.
+  // However, sampling texels from a linear texture to a srgb image, it will
+  // not convert linear to srgb automatically. Shader should always operates
+  // in linear space. So in encoder, we need to encode explicitly in shader.
+  const char* fs_source =
+      "#version 150\n"
+      "uniform sampler2D u_source_texture;\n"
+      "in vec2 v_texcoord;\n"
+      "out vec4 output_color;\n"
+      "\n"
+      "void main()\n"
+      "{\n"
+      "    vec4 c = texture(u_source_texture, v_texcoord);\n"
+      "    output_color = c;\n"
+      "}\n";
+
+  GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
+  CompileShader(fs, fs_source);
+  glAttachShader(srgb_decoder_program_, fs);
+  glDeleteShader(fs);
+
+  glLinkProgram(srgb_decoder_program_);
+#ifndef NDEBUG
+  GLint linked = 0;
+  glGetProgramiv(srgb_decoder_program_, GL_LINK_STATUS, &linked);
+  if (!linked) {
+    DLOG(ERROR) << "BlitFramebuffer: program link failure.";
+  }
+#endif
+
+  GLuint texture_uniform =
+      glGetUniformLocation(srgb_decoder_program_, "u_source_texture");
+  glUseProgram(srgb_decoder_program_);
+  glUniform1i(texture_uniform, 0);
+
+  glGenTextures(srgb_decoder_textures_.size(), srgb_decoder_textures_.data());
+  glActiveTexture(GL_TEXTURE0);
+  for (auto srgb_decoder_texture : srgb_decoder_textures_) {
+    glBindTexture(GL_TEXTURE_2D, srgb_decoder_texture);
+
+    // Use linear, non-mipmapped sampling with the srgb decoder texture
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+  }
+
+  glGenFramebuffersEXT(1, &srgb_decoder_fbo_);
+  glGenVertexArraysOES(1, &srgb_decoder_vao_);
+
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+
+  srgb_decoder_initialized_ = true;
+}
+
+void SRGBConverter::InitializeSRGBEncoder(const gles2::GLES2Decoder* decoder) {
+  if (srgb_encoder_initialized_) {
+    return;
+  }
+
+  srgb_encoder_program_ = glCreateProgram();
+
+  // Compile the vertex shader
+  GLuint vs = glCreateShader(GL_VERTEX_SHADER);
+  CompileShader(vs, vs_source);
+  glAttachShader(srgb_encoder_program_, vs);
+  glDeleteShader(vs);
+
+  // Compile the fragment shader
+
+  // Sampling texels from a srgb texture to a linear image, it will convert
+  // the srgb color space to linear color space automatically as a part of
+  // filtering. See the section <sRGB Texture Color Conversion> in GLES and
+  // OpenGL spec. So in decoder, we don't need to decode again.
+  // However, sampling texels from a linear texture to a srgb image, it will
+  // not convert linear to srgb automatically. Shader should always operates
+  // in linear space. So in encoder, we need to encode explicitly in shader.
+  const char* fs_source =
+      "#version 150\n"
+      "uniform sampler2D u_source_texture;\n"
+      "in vec2 v_texcoord;\n"
+      "out vec4 output_color;\n"
+      "\n"
+      "float encode(float color)\n"
+      "{\n"
+      "    float encoded_color;\n"
+      "    if (color <= 0.0) {\n"
+      "        return 0.0;\n"
+      "    } else if (color < 0.0031308) {\n"
+      "        return color * 12.92;\n"
+      "    } else if (color < 1) {\n"
+      "        return pow(color, 0.41666) * 1.055 - 0.055;\n"
+      "    } else {\n"
+      "        return 1.0;\n"
+      "    }\n"
+      "}\n"
+      "\n"
+      "void main()\n"
+      "{\n"
+      "    vec4 c = texture(u_source_texture, v_texcoord);\n"
+      "    output_color = vec4(encode(c.r), encode(c.g), encode(c.b), c.a);\n"
+      "}\n";
+
+  GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
+  CompileShader(fs, fs_source);
+  glAttachShader(srgb_encoder_program_, fs);
+  glDeleteShader(fs);
+
+  glLinkProgram(srgb_encoder_program_);
+#ifndef NDEBUG
+  GLint linked = 0;
+  glGetProgramiv(srgb_encoder_program_, GL_LINK_STATUS, &linked);
+  if (!linked) {
+    DLOG(ERROR) << "SRGB Encoder for BlitFramebuffer: program link failure.";
+  }
+#endif
+
+  GLuint texture_uniform =
+      glGetUniformLocation(srgb_encoder_program_, "u_source_texture");
+  glUseProgram(srgb_encoder_program_);
+  glUniform1i(texture_uniform, 0);
+
+  glGenTextures(srgb_encoder_textures_.size(), srgb_encoder_textures_.data());
+  glActiveTexture(GL_TEXTURE0);
+  for (auto srgb_encoder_texture : srgb_encoder_textures_) {
+    glBindTexture(GL_TEXTURE_2D, srgb_encoder_texture);
+
+    // Use linear, non-mipmapped sampling with the srgb encoder texture
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+  }
+
+  glGenFramebuffersEXT(1, &srgb_encoder_fbo_);
+  glGenVertexArraysOES(1, &srgb_encoder_vao_);
+
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+
+  srgb_encoder_initialized_ = true;
+}
+
+void SRGBConverter::Destroy() {
+  if (srgb_decoder_initialized_) {
+    glDeleteProgram(srgb_decoder_program_);
+    srgb_decoder_program_ = 0;
+
+    glDeleteTextures(srgb_decoder_textures_.size(),
+                     srgb_decoder_textures_.data());
+    srgb_decoder_textures_.fill(0);
+
+    glDeleteFramebuffersEXT(1, &srgb_decoder_fbo_);
+    srgb_decoder_fbo_ = 0;
+
+    glDeleteVertexArraysOES(1, &srgb_decoder_vao_);
+    srgb_decoder_vao_ = 0;
+
+    srgb_decoder_initialized_ = false;
+  }
+
+  if (srgb_encoder_initialized_) {
+    glDeleteProgram(srgb_encoder_program_);
+    srgb_encoder_program_ = 0;
+
+    glDeleteTextures(srgb_encoder_textures_.size(),
+                     srgb_encoder_textures_.data());
+    srgb_encoder_textures_.fill(0);
+
+    glDeleteFramebuffersEXT(1, &srgb_encoder_fbo_);
+    srgb_encoder_fbo_ = 0;
+
+    glDeleteVertexArraysOES(1, &srgb_encoder_vao_);
+    srgb_encoder_vao_ = 0;
+
+    srgb_encoder_initialized_ = false;
+  }
+}
+
+void SRGBConverter::SRGBToLinear(const gles2::GLES2Decoder* decoder,
+                                 GLint srcX0,
+                                 GLint srcY0,
+                                 GLint srcX1,
+                                 GLint srcY1,
+                                 GLint dstX0,
+                                 GLint dstY0,
+                                 GLint dstX1,
+                                 GLint dstY1,
+                                 GLbitfield mask,
+                                 GLenum filter,
+                                 const gfx::Size& framebuffer_size,
+                                 GLuint src_framebuffer,
+                                 GLenum src_framebuffer_internal_format,
+                                 GLuint dst_framebuffer) {
+  // This function blits srgb image in src fb to linear image in dst fb.
+  // The steps are:
+  // 1) Copy and crop pixels from source srgb image to the 1st texture(srgb).
+  // 2) Sampling from the 1st texture and drawing to the 2nd texture(linear).
+  //    During this step, color space is converted from srgb to linear.
+  // 3) Finally, blit pixels from the 2nd texture to the target, which is
+  //    also a linear image.
+  DCHECK(srgb_decoder_initialized_);
+
+  // Copy the image from read buffer to the decoder's 1st texture(srgb).
+  // TODO(yunchao) If the read buffer is a fbo texture, we can sample
+  // directly from that texture. In this way, we can save gpu memory.
+  glBindFramebufferEXT(GL_FRAMEBUFFER, src_framebuffer);
+  glActiveTexture(GL_TEXTURE0);
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[0]);
+
+  // We should not copy pixels outside of the read framebuffer. If we read
+  // these pixels, they would become in-bound during BlitFramebuffer. However,
+  // Out-of-bounds pixels will be initialized to 0 in CopyTexSubImage. But they
+  // should read as if the GL_CLAMP_TO_EDGE texture mapping mode were applied
+  // during BlitFramebuffer when the filter is GL_LINEAR.
+  GLuint x = srcX1 > srcX0 ? srcX0 : srcX1;
+  GLuint y = srcY1 > srcY0 ? srcY0 : srcY1;
+  GLuint width = srcX1 > srcX0 ? srcX1 - srcX0 : srcX0 - srcX1;
+  GLuint height = srcY1 > srcY0 ? srcY1 - srcY0 : srcY0 - srcY1;
+  gfx::Rect c(0, 0, framebuffer_size.width(), framebuffer_size.height());
+  c.Intersect(gfx::Rect(x, y, width, height));
+  GLuint xoffset = c.x() - x;
+  GLuint yoffset = c.y() - y;
+  glCopyTexImage2D(GL_TEXTURE_2D, 0, src_framebuffer_internal_format, c.x(),
+                   c.y(), c.width(), c.height(), 0);
+
+  // Make a temporary linear texture as the decoder's 2nd texture, where we
+  // render the converted (srgb to linear) result to.
+  glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
+
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[1]);
+  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, c.width(), c.height(), 0, GL_RGBA,
+               GL_UNSIGNED_BYTE, nullptr);
+  glBindFramebufferEXT(GL_FRAMEBUFFER, srgb_decoder_fbo_);
+  glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
+                            srgb_decoder_textures_[1], 0);
+
+  // Sampling from the decoder's first texture(srgb) and drawing to the
+  // decoder's 2nd texture(linear),
+  glUseProgram(srgb_decoder_program_);
+  glViewport(0, 0, width, height);
+  glDisable(GL_SCISSOR_TEST);
+  glDisable(GL_DEPTH_TEST);
+  glDisable(GL_STENCIL_TEST);
+  glDisable(GL_CULL_FACE);
+  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+  glDepthMask(GL_FALSE);
+  glDisable(GL_BLEND);
+  glDisable(GL_DITHER);
+
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[0]);
+  glBindVertexArrayOES(srgb_decoder_vao_);
+
+  glDrawArrays(GL_TRIANGLES, 0, 6);
+
+  // Finally, bind the decoder framebuffer as read framebuffer,
+  // blit the converted texture in decoder fbo to the destination texture
+  // in destination framebuffer.
+  glBindFramebufferEXT(GL_READ_FRAMEBUFFER, srgb_decoder_fbo_);
+  glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, dst_framebuffer);
+  // Note that the source region has been changed in decoder framebuffer.
+  // The xoffset/yoffset can make bliting clamp to the correct edge if
+  // CLAMP_TO_EDGE is necessary.
+  glBlitFramebuffer(srcX0 < srcX1 ? 0 - xoffset : width - xoffset,
+                    srcY0 < srcY1 ? 0 - yoffset : height - yoffset,
+                    srcX0 < srcX1 ? width - xoffset : 0 - xoffset,
+                    srcY0 < srcY1 ? height - yoffset : 0 - yoffset, dstX0,
+                    dstY0, dstX1, dstY1, mask, filter);
+
+  // Restore state
+  decoder->RestoreAllAttributes();
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+  decoder->RestoreBufferBindings();
+  decoder->RestoreFramebufferBindings();
+  decoder->RestoreGlobalState();
+}
+
+void SRGBConverter::LinearToSRGB(const gles2::GLES2Decoder* decoder,
+                                 GLint srcX0,
+                                 GLint srcY0,
+                                 GLint srcX1,
+                                 GLint srcY1,
+                                 GLint dstX0,
+                                 GLint dstY0,
+                                 GLint dstX1,
+                                 GLint dstY1,
+                                 GLbitfield mask,
+                                 GLenum filter,
+                                 GLuint src_framebuffer,
+                                 GLenum src_framebuffer_internal_format,
+                                 GLenum src_framebuffer_format,
+                                 GLenum src_framebuffer_type,
+                                 GLuint dst_framebuffer) {
+  // This function blits linear image in src fb to srgb image in dst fb.
+  // The steps are:
+  // 1) BlitFramebuffer from source linear image to a temp linear texture.
+  // 2) Sampling from the temp texture and drawing to the target srgb
+  //    image. During this step, color space is converted from linear to srgb.
+
+  DCHECK(srgb_encoder_initialized_);
+
+  // Create a temp linear texture as draw buffer. Blit framebuffer from
+  // source linear image to the temp linear texture. Filtering is done
+  // during bliting. Note that the src and dst coordinates may be reversed.
+  glActiveTexture(GL_TEXTURE0);
+  glBindTexture(GL_TEXTURE_2D, srgb_encoder_textures_[0]);
+
+  GLuint width = dstX1 > dstX0 ? dstX1 - dstX0 : dstX0 - dstX1;
+  GLuint height = dstY1 > dstY0 ? dstY1 - dstY0 : dstY0 - dstY1;
+  glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
+  glTexImage2D(GL_TEXTURE_2D, 0, src_framebuffer_internal_format, width, height,
+               0, src_framebuffer_format, src_framebuffer_type, nullptr);
+
+  glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, srgb_encoder_fbo_);
+  glFramebufferTexture2DEXT(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                            GL_TEXTURE_2D, srgb_encoder_textures_[0], 0);
+  glBindFramebufferEXT(GL_READ_FRAMEBUFFER, src_framebuffer);
+  glBlitFramebuffer(srcX0, srcY0, srcX1, srcY1, dstX0 < dstX1 ? 0 : width,
+                    dstY0 < dstY1 ? 0 : height, dstX0 < dstX1 ? width : 0,
+                    dstY0 < dstY1 ? height : 0, mask, filter);
+
+  // Sampling from the linear texture and drawing to the target srgb image.
+  // During this step, color space is converted from linear to srgb. We should
+  // set appropriate viewport to draw to the correct location in target FB.
+  GLuint xstart = dstX0 < dstX1 ? dstX0 : dstX1;
+  GLuint ystart = dstY0 < dstY1 ? dstY0 : dstY1;
+  glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, dst_framebuffer);
+  glUseProgram(srgb_encoder_program_);
+  glViewport(xstart, ystart, width, height);
+  glDisable(GL_SCISSOR_TEST);
+  glDisable(GL_DEPTH_TEST);
+  glDisable(GL_STENCIL_TEST);
+  glDisable(GL_CULL_FACE);
+  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+  glDepthMask(GL_FALSE);
+  glDisable(GL_BLEND);
+  glDisable(GL_DITHER);
+
+  glBindTexture(GL_TEXTURE_2D, srgb_encoder_textures_[0]);
+  glBindVertexArrayOES(srgb_encoder_vao_);
+
+  glDrawArrays(GL_TRIANGLES, 0, 6);
+
+  // Restore state
+  decoder->RestoreAllAttributes();
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+  decoder->RestoreBufferBindings();
+  decoder->RestoreFramebufferBindings();
+  decoder->RestoreGlobalState();
+}
+
+void SRGBConverter::SRGBToSRGB(const gles2::GLES2Decoder* decoder,
+                               GLint srcX0,
+                               GLint srcY0,
+                               GLint srcX1,
+                               GLint srcY1,
+                               GLint dstX0,
+                               GLint dstY0,
+                               GLint dstX1,
+                               GLint dstY1,
+                               GLbitfield mask,
+                               GLenum filter,
+                               const gfx::Size& framebuffer_size,
+                               GLuint src_framebuffer,
+                               GLenum src_framebuffer_internal_format,
+                               GLuint dst_framebuffer) {
+  // This function blits srgb image in src fb to srgb image in dst fb.
+  // It needs to use decoder's resource, as well as encoder's resources,
+  // for instance, decoder's and encoder's fbos, programs and textuers.
+  // The steps are:
+  // 1) Copy and crop pixels from source srgb image to the 1st texture(srgb).
+  // 2) Sampling from the 1st texture and drawing to the 2nd texture(linear).
+  //    During this step, color space is converted from srgb to linear.
+  // 3) Blit pixels from the 2nd texture to the 3rd texture(linear).
+  // 4) Sampling from the 3rd texture and drawing to the dst image(srgb).
+  //    During this step, color space is converted from linear to srgb.
+  DCHECK(srgb_decoder_initialized_ && srgb_encoder_initialized_);
+
+  // Copy the image from read buffer to the decoder's 1st texture(srgb).
+  // TODO(yunchao) If the read buffer is a fbo texture, we can sample
+  // directly from that texture. In this way, we can save gpu memory.
+  glBindFramebufferEXT(GL_FRAMEBUFFER, src_framebuffer);
+  glActiveTexture(GL_TEXTURE0);
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[0]);
+
+  // We should not copy pixels outside of the read framebuffer. If we read
+  // these pixels, they would become in-bound during BlitFramebuffer. However,
+  // Out-of-bounds pixels will be initialized to 0 in CopyTexSubImage. But they
+  // should read as if the GL_CLAMP_TO_EDGE texture mapping mode were applied
+  // during BlitFramebuffer when the filter is GL_LINEAR.
+  GLuint x = srcX1 > srcX0 ? srcX0 : srcX1;
+  GLuint y = srcY1 > srcY0 ? srcY0 : srcY1;
+  GLuint width_read = srcX1 > srcX0 ? srcX1 - srcX0 : srcX0 - srcX1;
+  GLuint height_read = srcY1 > srcY0 ? srcY1 - srcY0 : srcY0 - srcY1;
+  gfx::Rect c(0, 0, framebuffer_size.width(), framebuffer_size.height());
+  c.Intersect(gfx::Rect(x, y, width_read, height_read));
+  GLuint xoffset = c.x() - x;
+  GLuint yoffset = c.y() - y;
+  glCopyTexImage2D(GL_TEXTURE_2D, 0, src_framebuffer_internal_format, c.x(),
+                   c.y(), c.width(), c.height(), 0);
+
+  // Make a temporary linear texture as the decoder's 2nd texture, where we
+  // render the converted (srgb to linear) result to.
+  glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
+
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[1]);
+  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, c.width(), c.height(), 0, GL_RGBA,
+               GL_UNSIGNED_BYTE, nullptr);
+  glBindFramebufferEXT(GL_FRAMEBUFFER, srgb_decoder_fbo_);
+  glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
+                            srgb_decoder_textures_[1], 0);
+
+  // Sampling from the decoder's first texture(srgb) and drawing to the
+  // decoder's 2nd texture(linear),
+  glUseProgram(srgb_decoder_program_);
+  glViewport(0, 0, width_read, height_read);
+  glDisable(GL_SCISSOR_TEST);
+  glDisable(GL_DEPTH_TEST);
+  glDisable(GL_STENCIL_TEST);
+  glDisable(GL_CULL_FACE);
+  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+  glDepthMask(GL_FALSE);
+  glDisable(GL_BLEND);
+  glDisable(GL_DITHER);
+
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[0]);
+  glBindVertexArrayOES(srgb_decoder_vao_);
+
+  glDrawArrays(GL_TRIANGLES, 0, 6);
+
+  // Create the 3rd texture(linear) as decoder's draw buffer. Blit framebuffer
+  // from the 2nd texture(linear) to the 3rd texture. Filtering is done
+  // during bliting. Note that the src and dst coordinates may be reversed.
+  glBindTexture(GL_TEXTURE_2D, srgb_encoder_textures_[0]);
+
+  GLuint width_draw = dstX1 > dstX0 ? dstX1 - dstX0 : dstX0 - dstX1;
+  GLuint height_draw = dstY1 > dstY0 ? dstY1 - dstY0 : dstY0 - dstY1;
+  glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
+  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width_draw, height_draw, 0, GL_RGBA,
+               GL_UNSIGNED_BYTE, nullptr);
+
+  glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, srgb_encoder_fbo_);
+  glFramebufferTexture2DEXT(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                            GL_TEXTURE_2D, srgb_encoder_textures_[0], 0);
+  glBindFramebufferEXT(GL_READ_FRAMEBUFFER, srgb_decoder_fbo_);
+  glBlitFramebuffer(srcX0 < srcX1 ? 0 - xoffset : width_read - xoffset,
+                    srcY0 < srcY1 ? 0 - yoffset : height_read - yoffset,
+                    srcX0 < srcX1 ? width_read - xoffset : 0 - xoffset,
+                    srcY0 < srcY1 ? height_read - yoffset : 0 - yoffset,
+                    dstX0 < dstX1 ? 0 : width_draw,
+                    dstY0 < dstY1 ? 0 : height_draw,
+                    dstX0 < dstX1 ? width_draw : 0,
+                    dstY0 < dstY1 ? height_draw : 0, mask, filter);
+
+  // Sampling from the 3rd texture(linear) and drawing to the target srgb image.
+  // During this step, color space is converted from linear to srgb. We should
+  // set appropriate viewport to draw to the correct location in target FB.
+  GLuint xstart = dstX0 < dstX1 ? dstX0 : dstX1;
+  GLuint ystart = dstY0 < dstY1 ? dstY0 : dstY1;
+  glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, dst_framebuffer);
+  glUseProgram(srgb_encoder_program_);
+  glViewport(xstart, ystart, width_draw, height_draw);
+
+  glBindTexture(GL_TEXTURE_2D, srgb_encoder_textures_[0]);
+  glBindVertexArrayOES(srgb_encoder_vao_);
+
+  glDrawArrays(GL_TRIANGLES, 0, 6);
+
+  // Restore state
+  decoder->RestoreAllAttributes();
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+  decoder->RestoreBufferBindings();
+  decoder->RestoreFramebufferBindings();
+  decoder->RestoreGlobalState();
+}
+
+void SRGBConverter::SRGBGenerateMipmap(const gles2::GLES2Decoder* decoder,
+                                       Texture* tex,
+                                       GLenum target) {
+  DCHECK(srgb_decoder_initialized_);
+
+  GLsizei width;
+  GLsizei height;
+  GLsizei depth;
+  GLenum type = 0;
+  GLenum internal_format = 0;
+  GLsizei base_level = tex->base_level();
+  tex->GetLevelSize(target, base_level, &width, &height, &depth);
+  tex->GetLevelType(target, 0, &type, &internal_format);
+  const GLint mipmap_level =
+      TextureManager::ComputeMipMapCount(target, width, height, depth);
+
+  // copy tex to srgb_decoder_textures_[0] with srgb format
+  glBindTexture(target, tex->service_id());
+  glBindFramebufferEXT(GL_READ_FRAMEBUFFER, srgb_encoder_fbo_);

[yunchao, 2016/09/13 08:55:40]

decoder_fbo_

+  glFramebufferTexture2DEXT(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                            GL_TEXTURE_2D, tex->service_id(), 0);
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[0]);
+  glTexImage2D(GL_TEXTURE_2D, 0, internal_format, width, height, 0, GL_SRGB,
+               GL_UNSIGNED_BYTE, nullptr);
+  glCopyTexImage2D(GL_TEXTURE_2D, 0, internal_format, 0, 0, width, height, 0);
+
+  // bind srgb_decoder_textures_[1] to draw framebuffer
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[1]);
+  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA,
+               GL_UNSIGNED_BYTE, nullptr);
+  glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, srgb_decoder_fbo_);
+  glFramebufferTexture2DEXT(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                            GL_TEXTURE_2D, srgb_decoder_textures_[1], 0);
+  // bind tex with srgb format and render with srgb_decoder_program_
+  glUseProgram(srgb_decoder_program_);
+  glViewport(0, 0, width, height);
+  glDisable(GL_SCISSOR_TEST);
+  glDisable(GL_DEPTH_TEST);
+  glDisable(GL_STENCIL_TEST);
+  glDisable(GL_CULL_FACE);
+  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+  glDepthMask(GL_FALSE);
+  glDisable(GL_BLEND);
+  glDisable(GL_DITHER);
+
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[0]);

[yunchao, 2016/09/13 08:55:40]

bind VAO

+  glDrawArrays(GL_TRIANGLES, 0, 6);
+
+  // tex and srgb_decoder_textures_[1] generateMipmap
+  glBindTexture(GL_TEXTURE_2D, tex->service_id());
+  glGenerateMipmapEXT(GL_TEXTURE_2D);
+  glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[1]);
+  glGenerateMipmapEXT(GL_TEXTURE_2D);
+
+  // bind tex with rgba format and render with srgb_encoder_program_
+  InitializeSRGBEncoder(decoder);

[yunchao, 2016/09/13 08:55:40]

remove this line

+  glUseProgram(srgb_encoder_program_);
+  glViewport(0, 0, width, height);
+  glDisable(GL_SCISSOR_TEST);
+  glDisable(GL_DEPTH_TEST);
+  glDisable(GL_STENCIL_TEST);
+  glDisable(GL_CULL_FACE);
+  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+  glDepthMask(GL_FALSE);
+  glDisable(GL_BLEND);
+  glDisable(GL_DITHER);

[yunchao, 2016/09/13 08:55:40]

remove these code

+
+  glBindVertexArrayOES(srgb_encoder_vao_);
+
+  for (GLint level = base_level; level < mipmap_level; level++) {
+    glBindTexture(GL_TEXTURE_2D, tex->service_id());
+    glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, srgb_encoder_fbo_);
+    glFramebufferTexture2DEXT(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                              GL_TEXTURE_2D, tex->service_id(), level);
+
+    glActiveTexture(GL_TEXTURE0);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
+                    GL_NEAREST_MIPMAP_NEAREST);
+    glBindTexture(GL_TEXTURE_2D, srgb_decoder_textures_[1]);
+
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, level);

[yunchao, 2016/09/13 08:55:40]

This line can get the similar effect with the line NEAREST_MIPMAP_NEAREST.

+    glViewport(0, 0, width, height);
+    glDrawArrays(GL_TRIANGLES, 0, 6);
+    width /= 2;
+    height /= 2;
+  }
+
+  // Restore state
+  decoder->RestoreAllAttributes();
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+  decoder->RestoreBufferBindings();
+  decoder->RestoreFramebufferBindings();
+  decoder->RestoreGlobalState();
+}
+
+}  // namespace gles2.
+}  // namespace gpu