optimize precision for conversion from srgb to linear

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 {
@@ skipping 342 matching lines @@
   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, base_level, &type, &internal_format);
   const GLint mipmap_levels =
       TextureManager::ComputeMipMapCount(target, width, height, depth);
 
-  // bind srgb_decoder_textures_[1] to draw framebuffer
   glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
-  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA,
-               GL_UNSIGNED_BYTE, nullptr);
+  if (feature_info_->ext_color_buffer_float_available() &&
+      feature_info_->oes_texture_float_linear_available()) {
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, width, height, 0, GL_RGBA,
+                 GL_UNSIGNED_BYTE, nullptr);
+  } else {
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 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_converter_textures_[1], 0);
 
   // bind texture with srgb format and render with srgb_converter_program_
   glUseProgram(srgb_converter_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);
 
   glBindVertexArrayOES(srgb_converter_vao_);
   glActiveTexture(GL_TEXTURE0);
   glBindTexture(GL_TEXTURE_2D, tex->service_id());
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 
   glDrawArrays(GL_TRIANGLES, 0, 6);
 
-  // generateMipmap for srgb_decoder_textures_[1]
   glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
   glGenerateMipmapEXT(GL_TEXTURE_2D);
 
   // bind tex with rgba format and render with srgb_converter_program_
   glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, srgb_encoder_fbo_);
   glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                   GL_NEAREST_MIPMAP_NEAREST);
   width >>= 1;
   height >>= 1;
@@ skipping 23 matching lines @@
   decoder->RestoreActiveTexture();
   decoder->RestoreProgramBindings();
   decoder->RestoreBufferBindings();
   decoder->RestoreFramebufferBindings();
   decoder->RestoreGlobalState();
   decoder->RestoreTextureState(tex->service_id());
 }
 
 }  // namespace gles2.
 }  // namespace gpu