From 6a3088cbd0111e516d8e75d8a7aaede2aea54818 Mon Sep 17 00:00:00 2001
From: Sally Qi <sallyqi@google.com>
Date: Mon, 28 Mar 2022 22:11:22 -0700
Subject: [PATCH] Add HLG transfer function to proper dataspace

- fix the issue of color washout in the textureview
- scale down hlg to [0, 1] in skia
- app side should enable wideColorGamut for it

Bug: 224841108
Test: test HLG video on Instagram
Change-Id: If9da8495139a0579667c64dcd8a61e9554b7da58
---
 libs/hwui/utils/Color.cpp | 26 +++++++++++++++++++++++++-
 libs/hwui/utils/Color.h   |  3 +++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/libs/hwui/utils/Color.cpp b/libs/hwui/utils/Color.cpp
index 2293ace0bd16b..28f547703dde0 100644
--- a/libs/hwui/utils/Color.cpp
+++ b/libs/hwui/utils/Color.cpp
@@ -165,6 +165,14 @@ android_dataspace ColorSpaceToADataSpace(SkColorSpace* colorSpace, SkColorType c
         if (SkColorSpace::Equals(colorSpace, rec2020PQ.get())) {
             return HAL_DATASPACE_BT2020_PQ;
         }
+        // HLG
+        const auto hlgFn = GetHLGScaleTransferFunction();
+        if (hlgFn.has_value()) {
+            auto rec2020HLG = SkColorSpace::MakeRGB(hlgFn.value(), SkNamedGamut::kRec2020);
+            if (SkColorSpace::Equals(colorSpace, rec2020HLG.get())) {
+                return static_cast<android_dataspace>(HAL_DATASPACE_BT2020_HLG);
+            }
+        }
         LOG_ALWAYS_FATAL("Only select non-numerical transfer functions are supported");
     }
 
@@ -247,6 +255,14 @@ sk_sp<SkColorSpace> DataSpaceToColorSpace(android_dataspace dataspace) {
             return nullptr;
     }
 
+    // HLG
+    if ((dataspace & HAL_DATASPACE_TRANSFER_MASK) == HAL_DATASPACE_TRANSFER_HLG) {
+        const auto hlgFn = GetHLGScaleTransferFunction();
+        if (hlgFn.has_value()) {
+            return SkColorSpace::MakeRGB(hlgFn.value(), gamut);
+        }
+    }
+
     switch (dataspace & HAL_DATASPACE_TRANSFER_MASK) {
         case HAL_DATASPACE_TRANSFER_LINEAR:
             return SkColorSpace::MakeRGB(SkNamedTransferFn::kLinear, gamut);
@@ -264,7 +280,6 @@ sk_sp<SkColorSpace> DataSpaceToColorSpace(android_dataspace dataspace) {
             return SkColorSpace::MakeRGB(SkNamedTransferFn::kRec2020, gamut);
         case HAL_DATASPACE_TRANSFER_UNSPECIFIED:
             return nullptr;
-        case HAL_DATASPACE_TRANSFER_HLG:
         default:
             ALOGV("Unsupported Gamma: %d", dataspace);
             return nullptr;
@@ -381,5 +396,14 @@ skcms_TransferFunction GetPQSkTransferFunction(float sdr_white_level) {
     return fn;
 }
 
+// Skia skcms' default HLG maps encoded [0, 1] to linear [1, 12] in order to follow ARIB
+// but LinearEffect expects a decoded [0, 1] range instead to follow Rec 2100.
+std::optional<skcms_TransferFunction> GetHLGScaleTransferFunction() {
+    std::optional<skcms_TransferFunction> hlgFn = {};
+    skcms_TransferFunction_makeScaledHLGish(&hlgFn.value(), 1.f / 12.f, 2.f, 2.f, 1.f / 0.17883277f,
+                                            0.28466892f, 0.55991073f);
+    return hlgFn;
+}
+
 }  // namespace uirenderer
 }  // namespace android
diff --git a/libs/hwui/utils/Color.h b/libs/hwui/utils/Color.h
index 1654072fd2643..00f910f45c382 100644
--- a/libs/hwui/utils/Color.h
+++ b/libs/hwui/utils/Color.h
@@ -23,6 +23,8 @@
 #include <math.h>
 #include <system/graphics.h>
 
+#include <optional>
+
 struct ANativeWindow_Buffer;
 struct AHardwareBuffer_Desc;
 
@@ -127,6 +129,7 @@ struct Lab {
 Lab sRGBToLab(SkColor color);
 SkColor LabToSRGB(const Lab& lab, SkAlpha alpha);
 skcms_TransferFunction GetPQSkTransferFunction(float sdr_white_level = 0.f);
+std::optional<skcms_TransferFunction> GetHLGScaleTransferFunction();
 
 } /* namespace uirenderer */
 } /* namespace android */