Treat HLG images as 2.2 gamma on SDR displays.

This dramatically improves the quality of these images and is a
simple fix until real tone mapping can be provided.

Bug: 1216691
Change-Id: I8bde11bf4649f46115775d45472c099489b25a1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3297063
Reviewed-by: ccameron <ccameron@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#944819}

cc/paint/paint_image.cc

@@ -316,7 +316,10 @@ int PaintImage::height() const {
              : GetSkImageInfo().height();
 }
 
-gfx::ContentColorUsage PaintImage::GetContentColorUsage() const {
+gfx::ContentColorUsage PaintImage::GetContentColorUsage(bool* is_hlg) const {
+  if (is_hlg)
+    *is_hlg = false;
+
   // Right now, JS paint worklets can only be in sRGB
   if (paint_worklet_input_)
     return gfx::ContentColorUsage::kSRGB;
@@ -328,10 +331,15 @@ gfx::ContentColorUsage PaintImage::GetContentColorUsage() const {
     return gfx::ContentColorUsage::kSRGB;
 
   skcms_TransferFunction fn;
-  if (!color_space->isNumericalTransferFn(&fn) &&
-      (skcms_TransferFunction_isPQish(&fn) ||
-       skcms_TransferFunction_isHLGish(&fn))) {
-    return gfx::ContentColorUsage::kHDR;
+  if (!color_space->isNumericalTransferFn(&fn)) {
+    if (skcms_TransferFunction_isPQish(&fn))
+      return gfx::ContentColorUsage::kHDR;
+
+    if (skcms_TransferFunction_isHLGish(&fn)) {
+      if (is_hlg)
+        *is_hlg = true;
+      return gfx::ContentColorUsage::kHDR;
+    }
   }
 
   // If it's not HDR and not SRGB, report it as WCG.

cc/paint/paint_image.h

@@ -282,7 +282,7 @@ class CC_PAINT_EXPORT PaintImage {
     return paint_worklet_input_ ? nullptr : GetSkImageInfo().colorSpace();
   }
 
-  gfx::ContentColorUsage GetContentColorUsage() const;
+  gfx::ContentColorUsage GetContentColorUsage(bool* is_hlg = nullptr) const;
 
   // Returns whether this image will be decoded and rendered from YUV data
   // and fills out |info|. |supported_data_types| indicates the bit depths and

cc/tiles/gpu_image_decode_cache.cc

@@ -2934,14 +2934,28 @@ sk_sp<SkColorSpace> GpuImageDecodeCache::ColorSpaceForImageDecode(
 
 bool GpuImageDecodeCache::NeedsColorSpaceAdjustedForUpload(
     const DrawImage& image) const {
-  return image.sdr_white_level() != gfx::ColorSpace::kDefaultSDRWhiteLevel &&
-         image.paint_image().GetContentColorUsage() ==
-             gfx::ContentColorUsage::kHDR;
+  bool is_hlg = false;
+  if (image.paint_image().GetContentColorUsage(&is_hlg) !=
+      gfx::ContentColorUsage::kHDR) {
+    return false;
+  }
+
+  // Attempt basic "tonemapping" of HLG content when rendering to SDR.
+  if (is_hlg && !image.target_color_space().IsHDR())
+    return true;
+
+  return image.sdr_white_level() != gfx::ColorSpace::kDefaultSDRWhiteLevel;
 }
 
 sk_sp<SkColorSpace> GpuImageDecodeCache::ColorSpaceForImageUpload(
     const DrawImage& image) const {
   DCHECK(NeedsColorSpaceAdjustedForUpload(image));
+  if (!image.target_color_space().IsHDR()) {
+    // HLG is designed such that treating it as 2.2 gamma content works well.
+    constexpr skcms_TransferFunction kGamma22 = {2.2, 1, 0, 0, 0, 0, 0};
+    return SkColorSpace::MakeRGB(kGamma22, SkNamedGamut::kRec2020);
+  }
+
   return gfx::ColorSpace(*image.paint_image().color_space())
       .GetWithSDRWhiteLevel(image.sdr_white_level())
       .ToSkColorSpace();