Adjust screenshot behavior of HDR content

Cap the max amount of HDR headroom beyond which the
layer is clipped. This avoids over-dimming the SDR content
range in the resulting SDR screenshot

Test: screenshot of silkfx
Bug: 286942637
Change-Id: I67df32d9c192da18df516972ed92e9bd64063186

2 files changed, 10 insertions, 1 deletions

diff --git a/libs/renderengine/skia/SkiaRenderEngine.cpp b/libs/renderengine/skia/SkiaRenderEngine.cpp
index 5854135afe..fda6ea189e 100644
--- a/libs/renderengine/skia/SkiaRenderEngine.cpp
+++ b/libs/renderengine/skia/SkiaRenderEngine.cpp
@@ -86,6 +86,7 @@ namespace {
 // Debugging settings
 static const bool kPrintLayerSettings = false;
 static const bool kFlushAfterEveryLayer = kPrintLayerSettings;
+static constexpr bool kEnableLayerBrightening = true;
 
 } // namespace
 
@@ -699,7 +700,8 @@ void SkiaRenderEngine::drawLayersInternal(
 
     // ...and compute the dimming ratio if dimming is requested
     const float displayDimmingRatio = display.targetLuminanceNits > 0.f &&
-                    maxLayerWhitePoint > 0.f && display.targetLuminanceNits > maxLayerWhitePoint
+                    maxLayerWhitePoint > 0.f &&
+                    (kEnableLayerBrightening || display.targetLuminanceNits > maxLayerWhitePoint)
             ? maxLayerWhitePoint / display.targetLuminanceNits
             : 1.f;
 
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 79378befcc..fe2db940f7 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -7419,6 +7419,13 @@ ftl::SharedFuture<FenceResult> SurfaceFlinger::renderScreenImpl(
                                       renderArea->getHintForSeamlessTransition());
             sdrWhitePointNits = state.sdrWhitePointNits;
             displayBrightnessNits = state.displayBrightnessNits;
+            if (sdrWhitePointNits > 1.0f) {
+                // Restrict the amount of HDR "headroom" in the screenshot to avoid over-dimming
+                // the SDR portion. 2.0 chosen by experimentation
+                constexpr float kMaxScreenshotHeadroom = 2.0f;
+                displayBrightnessNits =
+                        std::min(sdrWhitePointNits * kMaxScreenshotHeadroom, displayBrightnessNits);
+            }
 
             if (requestedDataspace == ui::Dataspace::UNKNOWN) {
                 renderIntent = state.renderIntent;