Add sysprop to control HDR headroom

To accelerate tuning of the value allow it to be sysprop driven

Bug: 273624684
Test: change prop, verify silkfx headroom changes after re-launch
Change-Id: Ibad662b7ba06bd821c7a3ce48c19f4c94c716b5e

libs/hwui/Properties.cpp

@@ -91,6 +91,8 @@ bool Properties::isHighEndGfx = true;
 bool Properties::isLowRam = false;
 bool Properties::isSystemOrPersistent = false;
 
+float Properties::maxHdrHeadroomOn8bit = 5.f;  // TODO: Refine this number
+
 StretchEffectBehavior Properties::stretchEffectBehavior = StretchEffectBehavior::ShaderHWUI;
 
 DrawingEnabled Properties::drawingEnabled = DrawingEnabled::NotInitialized;
@@ -150,6 +152,11 @@ bool Properties::load() {
 
     enableWebViewOverlays = base::GetBoolProperty(PROPERTY_WEBVIEW_OVERLAYS_ENABLED, true);
 
+    auto hdrHeadroom = (float)atof(base::GetProperty(PROPERTY_8BIT_HDR_HEADROOM, "").c_str());
+    if (hdrHeadroom >= 1.f) {
+        maxHdrHeadroomOn8bit = std::min(hdrHeadroom, 100.f);
+    }
+
     // call isDrawingEnabled to force loading of the property
     isDrawingEnabled();
 

libs/hwui/Properties.h

@@ -218,6 +218,8 @@ enum DebugLevel {
 
 #define PROPERTY_MEMORY_POLICY "debug.hwui.app_memory_policy"
 
+#define PROPERTY_8BIT_HDR_HEADROOM "debug.hwui.8bit_hdr_headroom"
+
 ///////////////////////////////////////////////////////////////////////////////
 // Misc
 ///////////////////////////////////////////////////////////////////////////////
@@ -321,6 +323,8 @@ public:
     static bool isLowRam;
     static bool isSystemOrPersistent;
 
+    static float maxHdrHeadroomOn8bit;
+
     static StretchEffectBehavior getStretchEffectBehavior() {
         return stretchEffectBehavior;
     }

libs/hwui/renderthread/CanvasContext.cpp

@@ -311,7 +311,7 @@ float CanvasContext::setColorMode(ColorMode mode) {
     }
     switch (mColorMode) {
         case ColorMode::Hdr:
-            return 3.f;  // TODO: Refine this number
+            return Properties::maxHdrHeadroomOn8bit;
         case ColorMode::Hdr10:
             return 10.f;
         default: