[Command Buffer] emulate SRGB color format for BlitFramebuffer in OpenGL

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
new file mode 100644
index 0000000000000000000000000000000000000000..ecadd063a55769280844ed2ae62ad8adc407f868
--- /dev/null
+++ b/gpu/command_buffer/service/gles2_cmd_srgb_converter.cc
@@ -0,0 +1,329 @@
+// 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() {}
+
+
+
+void SRGBConverter::InitializeSRGBConverterProgram() {
+  if (srgb_converter_program_) {
+    return;
+  }
+
+  srgb_converter_program_ = glCreateProgram();
+
+  // Compile the vertex shader
+  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"

[Ken Russell (switch to Gerrit), 2016/09/16 22:32:29]

Embedding the vertex positions in the vertex shader seems a little too clever --
is there a good reason to not just allocate a small buffer object and hook it up
to the VAO you're already allocating?

[piman, 2016/09/16 22:53:29]

I'm actually ok with this. That's also done in the CopyTexImageResourceManager
and other places. Personally, I think it is simpler, and actually likely more
efficient, than managing a vertex buffer, its lifetime, its bindings, its
updates.

[Ken Russell (switch to Gerrit), 2016/09/16 23:19:42]

OK, fine by me then.

+      "    );\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";
+  GLuint vs = glCreateShader(GL_VERTEX_SHADER);
+  CompileShader(vs, vs_source);
+  glAttachShader(srgb_converter_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 during decoding, we don't need to use the equation to
+  // explicitly decode srgb to linear in fragment shader.
+  // Drawing to a srgb image, it will convert linear to srgb automatically.
+  // See the section <sRGB Conversion> in GLES and OpenGL spec. So during
+  // encoding, we don't need to use the equation to explicitly encode linear
+  // to srgb in fragment shader.
+  // As a result, we just use a simple fragment shader to do srgb conversion.
+  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_converter_program_, fs);
+  glDeleteShader(fs);
+
+  glLinkProgram(srgb_converter_program_);
+#ifndef NDEBUG
+  GLint linked = 0;
+  glGetProgramiv(srgb_converter_program_, GL_LINK_STATUS, &linked);
+  if (!linked) {
+    DLOG(ERROR) << "BlitFramebuffer: program link failure.";
+  }
+#endif
+
+  GLuint texture_uniform =
+      glGetUniformLocation(srgb_converter_program_, "u_source_texture");
+  glUseProgram(srgb_converter_program_);
+  glUniform1i(texture_uniform, 0);
+}
+
+void SRGBConverter::InitializeSRGBConverter(
+    const gles2::GLES2Decoder* decoder) {
+  if (srgb_converter_initialized_) {
+    return;
+  }
+
+  InitializeSRGBConverterProgram();
+
+  glGenTextures(
+      srgb_converter_textures_.size(), srgb_converter_textures_.data());
+  glActiveTexture(GL_TEXTURE0);
+  for (auto srgb_converter_texture : srgb_converter_textures_) {
+    glBindTexture(GL_TEXTURE_2D, srgb_converter_texture);
+
+    // Use linear, non-mipmapped sampling with the srgb converter 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_);
+  glGenFramebuffersEXT(1, &srgb_encoder_fbo_);
+
+  glGenVertexArraysOES(1, &srgb_converter_vao_);
+
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+
+  srgb_converter_initialized_ = true;
+}
+
+void SRGBConverter::Destroy() {
+  if (srgb_converter_initialized_) {
+    glDeleteTextures(srgb_converter_textures_.size(),
+                     srgb_converter_textures_.data());
+    srgb_converter_textures_.fill(0);
+
+    glDeleteFramebuffersEXT(1, &srgb_decoder_fbo_);
+    srgb_decoder_fbo_ = 0;
+    glDeleteFramebuffersEXT(1, &srgb_encoder_fbo_);
+    srgb_encoder_fbo_ = 0;
+
+    glDeleteVertexArraysOES(1, &srgb_converter_vao_);
+    srgb_converter_vao_ = 0;
+
+    glDeleteProgram(srgb_converter_program_);
+    srgb_converter_program_ = 0;
+
+    srgb_converter_initialized_ = false;
+  }
+}
+
+void SRGBConverter::Blit(
+    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,
+    GLenum src_framebuffer_format,
+    GLenum src_framebuffer_type,
+    GLuint dst_framebuffer,
+    bool decode,
+    bool encode) {
+  // This function blits srgb image in src fb to srgb 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) 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_);
+
+  // 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);
+  glDisable(GL_DITHER);
+
+  // Copy the image from read buffer to the 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.
+  GLuint width_read = 0, height_read = 0, xoffset = 0, yoffset = 0;
+  if (decode) {
+    glBindFramebufferEXT(GL_FRAMEBUFFER, src_framebuffer);
+    glBindTexture(GL_TEXTURE_2D, srgb_converter_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;
+    width_read = srcX1 > srcX0 ? srcX1 - srcX0 : srcX0 - srcX1;
+    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));
+    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,
+                 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);
+
+    glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[0]);
+    glBindVertexArrayOES(srgb_converter_vao_);
+
+    glDrawArrays(GL_TRIANGLES, 0, 6);
+  }
+
+  // Create the 3rd texture(linear) as encoder_fbo's draw buffer. But we can
+  // reuse the 1st texture and re-allocate the image. Then 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.
+  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,
+        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);
+  // Set approriate read/draw framebuffer if decoding or encoding is skipped.
+  } else {
+    glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, dst_framebuffer);
+  }
+
+  if (decode) {
+    glBindFramebufferEXT(GL_READ_FRAMEBUFFER, srgb_decoder_fbo_);

[piman, 2016/09/16 20:49:27]

nit: this is already done in the decode path (srgb_decoder_fbo_ gets bound to
GL_FRAMEBUFFER, which means it's bound to both GL_READ_FRAMEBUFFER and
GL_DRAW_FRAMEBUFFER). So maybe the else clause below could move to l.257, such
that it goes

if (decode) {
  // ...
  // [do the copy/crop]
  // ...
  glBindFramebufferEXT(GL_FRAMEBUFFER, srgb_decoder_fbo_);
  // ...
  // [do the decode draw]
  // ...
} else {
  glBindFramebufferEXT(GL_READ_FRAMEBUFFER, src_framebuffer);
}
  

[yunchao, 2016/09/17 15:14:13]

Done.

+  } else {
+    glBindFramebufferEXT(GL_READ_FRAMEBUFFER, src_framebuffer);
+  }
+
+  glBlitFramebuffer(
+      decode ? (srcX0 < srcX1 ? 0 - xoffset : width_read - xoffset) : srcX0,
+      decode ? (srcY0 < srcY1 ? 0 - yoffset : height_read - yoffset) : srcY0,
+      decode ? (srcX0 < srcX1 ? width_read - xoffset : 0 - xoffset) : srcX1,
+      decode ? (srcY0 < srcY1 ? height_read - yoffset : 0 - yoffset) : srcY1,
+      encode ? (dstX0 < dstX1 ? 0 : width_draw) : dstX0,
+      encode ? (dstY0 < dstY1 ? 0 : height_draw) : dstY0,
+      encode ? (dstX0 < dstX1 ? width_draw : 0) : dstX1,
+      encode ? (dstY0 < dstY1 ? height_draw : 0) : dstY1,
+      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.
+  if (encode) {
+    GLuint xstart = dstX0 < dstX1 ? dstX0 : dstX1;
+    GLuint ystart = dstY0 < dstY1 ? dstY0 : dstY1;
+    glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER, dst_framebuffer);
+    glUseProgram(srgb_converter_program_);
+    glViewport(xstart, ystart, width_draw, height_draw);
+
+    glBindTexture(GL_TEXTURE_2D, srgb_converter_textures_[0]);
+    glBindVertexArrayOES(srgb_converter_vao_);
+
+    glDrawArrays(GL_TRIANGLES, 0, 6);
+  }
+
+  // Restore state
+  decoder->RestoreAllAttributes();
+  decoder->RestoreTextureUnitBindings(0);
+  decoder->RestoreActiveTexture();
+  decoder->RestoreProgramBindings();
+  decoder->RestoreBufferBindings();
+  decoder->RestoreFramebufferBindings();
+  decoder->RestoreGlobalState();
+}
+
+}  // namespace gles2.
+}  // namespace gpu