Use high precision texture format during srgb conversion emulation for blitFramebuffer

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 180 matching lines @@
   // 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.
   // If we need to blit from linear to srgb or vice versa, some steps will be
   // skipped.
   DCHECK(srgb_converter_initialized_);
+  // Use RGBA32F as the temp texture's internalformat to prevent precision
+  // loss during srgb conversion. But it is not color-renderable and
+  // texture-filterable in ES context.
+  DCHECK(!feature_info_->gl_version_info().is_es);
 
   // Set the states
   glActiveTexture(GL_TEXTURE0);
   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);
@@ skipping 21 matching lines @@
     xoffset = c.x() - x;
     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 2nd texture, where we
     // render the converted (srgb to linear) result to.
     glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 
     glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
-    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F,
                  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_converter_textures_[1], 0);
 
     // Sampling from the 1st texture(srgb) and drawing to the
     // 2nd texture(linear),
     glUseProgram(srgb_converter_program_);
     glViewport(0, 0, width_read, height_read);
@@ skipping 12 matching lines @@
   // from the 2nd texture(linear) to the 3rd texture. Filtering is done
   // during bliting. Note that the src and dst coordinates may be reversed.
   GLuint width_draw = 0, height_draw = 0;
   if (encode) {
     glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[0]);
 
     width_draw = dstX1 > dstX0 ? dstX1 - dstX0 : dstX0 - dstX1;
     height_draw = dstY1 > dstY0 ? dstY1 - dstY0 : dstY0 - dstY1;
     glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
     glTexImage2D(
-        GL_TEXTURE_2D, 0, decode ? GL_RGBA : src_framebuffer_internal_format,
+        GL_TEXTURE_2D, 0, decode ? GL_RGBA32F : src_framebuffer_internal_format,
         width_draw, height_draw, 0,
         decode ? GL_RGBA : src_framebuffer_format,
         decode ? GL_UNSIGNED_BYTE : src_framebuffer_type,
         nullptr);
 
     glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, srgb_encoder_fbo_);
     glFramebufferTexture2DEXT(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                               GL_TEXTURE_2D, srgb_converter_textures_[0], 0);
   } else {
     // Set approriate draw framebuffer if encoding is skipped.
@@ skipping 134 matching lines @@
   decoder->RestoreActiveTexture();
   decoder->RestoreProgramBindings();
   decoder->RestoreBufferBindings();
   decoder->RestoreFramebufferBindings();
   decoder->RestoreGlobalState();
   decoder->RestoreTextureState(tex->service_id());
 }
 
 }  // namespace gles2.
 }  // namespace gpu