emulate srgb format for generateMipmap

gpu/command_buffer/service/gles2_cmd_srgb_converter.cc

Index: gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc b/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
index 949d2d081341379edc51159ca976cbb7df4dc3d4..5ffbb47de31545874f7b9c2a2b5ac981c4a40b7d 100644
--- a/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
+++ b/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
@@ -331,5 +331,99 @@ void SRGBConverter::Blit(
   decoder->RestoreGlobalState();
 }
 
+void SRGBConverter::GenerateMipmap(const gles2::GLES2Decoder* decoder,
+                                   Texture* tex,
+                                   GLenum target) {
+  // This function generateMipmap for srgb texture.
+  // The steps are:
+  // 1) Do sampling from the base level of the sRGB texture and draw into
+  // a linear texture. During sampling, the sRGB format is converted to
+  // Linear format
+  // 2) Perform the glGenerateMipmap call against the linear texture
+  // 3) Iterate each mipmap level of the linear texture and draw back into
+  // the sRGB texture's corresponding mipmap. During drawing, the linear
+  // format is converted to sRGB format
+  DCHECK(srgb_converter_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, 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);
+  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;
+
+  // TODO(yizhou): An optimization. Attach 1 level at a time, once for every
+  // iteration of the loop.
+  for (GLint level = base_level + 1; level < base_level + mipmap_levels;
+       ++level) {
+    // copy mipmaps level by level from srgb_converter_textures_[1] to tex
+    // generate mipmap for tex manually
+    glBindTexture(GL_TEXTURE_2D, tex->service_id());
+    glTexImage2D(GL_TEXTURE_2D, level, internal_format, width, height, 0,
+                 GL_SRGB, type, NULL);
+    glFramebufferTexture2DEXT(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                              GL_TEXTURE_2D, tex->service_id(), level);
+
+    glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[1]);
+    glViewport(0, 0, width, height);
+    glDrawArrays(GL_TRIANGLES, 0, 6);
+    width >>= 1;
+    height >>= 1;
+  }
+
+  // Restore state
+  decoder->RestoreAllAttributes();
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+  decoder->RestoreBufferBindings();
+  decoder->RestoreFramebufferBindings();
+  decoder->RestoreGlobalState();
+  decoder->RestoreTextureState(tex->service_id());
+}
+
 }  // namespace gles2.
 }  // namespace gpu