Video Color Managament

cc/output/color_lut_cache.cc

+// Copyright 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 "cc/output/color_lut_cache.h"
+
+#include <stdint.h>
+#include <vector>
+
+#include "gpu/command_buffer/client/gles2_interface.h"
+#include "ui/gfx/color_transform.h"
+
+// After a LUT has not been used for this many frames, we release it.
+const uint32_t kMaxFramesUnused = 10;
+
+ColorLUTCache::ColorLUTCache(gpu::gles2::GLES2Interface* gl)
+    : lut_cache_(0), gl_(gl) {}
+
+ColorLUTCache::~ColorLUTCache() {
+  GLuint textures[10];
+  size_t n = 0;
+  for (const auto& cache_entry : lut_cache_) {
+    textures[n++] = cache_entry.second.first;
+    if (n == arraysize(textures)) {
+      gl_->DeleteTextures(n, textures);
+      n = 0;
+    }
+  }
+  if (n)
+    gl_->DeleteTextures(n, textures);
+}
+
+namespace {
+
+unsigned char FloatToLUT(float f) {
+  return std::min<int>(255, std::max<int>(0, floorf(f * 255.0f + 0.5f)));
+}
+};
+
+unsigned int ColorLUTCache::MakeLUT(const gfx::ColorSpace& from,
+                                    gfx::ColorSpace to,
+                                    int lut_samples) {
+  if (to == gfx::ColorSpace()) {
+    to = gfx::ColorSpace::CreateSRGB();
+  }
+  std::unique_ptr<gfx::ColorTransform> transform(
+      gfx::ColorTransform::NewColorTransform(
+          from, to, gfx::ColorTransform::Intent::PERCEPTUAL));
+
+  int lut_entries = lut_samples * lut_samples * lut_samples;
+  float inverse = 1.0f / (lut_samples - 1);
+  std::vector<unsigned char> lut(lut_entries * 4);
+  std::vector<gfx::ColorTransform::TriStim> samples(lut_samples * 3);
+  unsigned char* lutp = lut.data();
+  for (int y = 0; y < lut_samples; y++) {
+    for (int v = 0; v < lut_samples; v++) {
+      for (int u = 0; u < lut_samples; u++) {
+        samples[u].set_x(y * inverse);
+        samples[u].set_y(u * inverse);
+        samples[u].set_z(v * inverse);
+      }
+      transform->transform(samples.data(), samples.size());
+      for (int u = 0; u < lut_samples; u++) {
+        *(lutp++) = FloatToLUT(samples[u].x());
+        *(lutp++) = FloatToLUT(samples[u].y());
+        *(lutp++) = FloatToLUT(samples[u].z());
+        *(lutp++) = 255;  // alpha
+      }
+    }
+  }
+
+  unsigned int lut_texture;
+  gl_->GenTextures(1, &lut_texture);
+  gl_->BindTexture(GL_TEXTURE_2D, lut_texture);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+  gl_->TexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, lut_samples,
+                  lut_samples * lut_samples, 0, GL_RGBA, GL_UNSIGNED_BYTE,
+                  lut.data());

[ccameron, 2016/08/08 18:45:07]

We should be using GL_TEXTURE_3D for the lut -- then we can sample using a vec3,
and we don't have to do any work to clamp the R coordinate.

[hubbe, 2016/08/08 19:45:38]

No we should not, GL_TEXTURE_3D has absolutely awful performance on some
platforms, which is why skia doesn't use it in it's 3d-lut implementation
either.

+  return lut_texture;
+}
+
+unsigned int ColorLUTCache::GetLUT(const gfx::ColorSpace& from,
+                                   const gfx::ColorSpace& to,
+                                   int lut_samples) {
+  CacheKey key(from, std::make_pair(to, lut_samples));
+  auto iter = lut_cache_.Get(key);
+  if (iter != lut_cache_.end()) {
+    iter->second.second = current_frame_;
+    return iter->second.first;
+  }
+
+  unsigned int lut = MakeLUT(from, to, lut_samples);
+  lut_cache_.Put(key, std::make_pair(lut, current_frame_));
+  return lut;
+}
+
+void ColorLUTCache::Swap() {
+  current_frame_++;
+  while (!lut_cache_.empty() &&
+         current_frame_ - lut_cache_.rbegin()->second.first >
+             kMaxFramesUnused) {
+    gl_->DeleteTextures(1, &lut_cache_.rbegin()->second.first);
+    lut_cache_.ShrinkToSize(lut_cache_.size() - 1);
+  }
+}