Don't overdim SDR content in an HLG screenshot.

Aligning HLG and PQ to 1.0 == 203 nits made SDR assets in screenshots
too dim, since both the colorspace and the color transform applied
dimming. Removing dimming application from the color transform is a
larger change, so just compensate when configuring the screenshot in
SurfaceFlinger instead.

Bug: 280347733
Test: HwAccelerationTest
Test: Navigate in and out of recents
Change-Id: Idfdb74c0c3b977717b870b2bb9a469be37d27dc9

2 files changed, 15 insertions, 1 deletions

diff --git a/libs/shaders/shaders.cpp b/libs/shaders/shaders.cpp
index b8f2be111e..c85517a976 100644
--- a/libs/shaders/shaders.cpp
+++ b/libs/shaders/shaders.cpp
@@ -103,10 +103,14 @@ static void generateLuminanceNormalizationForOOTF(ui::Dataspace inputDataspace,
                     // tonemapping downstream.
                     // BT. 2100-2 operates on normalized luminances, so renormalize to the input to
                     // correctly adjust gamma.
+                    // Note that following BT. 2408 for HLG OETF actually maps 0.75 == ~264.96 nits,
+                    // rather than 203 nits, because 203 nits == OOTF(invOETF(0.75)), so even though
+                    // we originally scaled by 203 nits we need to re-normalize to 264.96 nits when
+                    // converting to the correct brightness range.
                     shader.append(R"(
                             float3 NormalizeLuminance(float3 xyz) {
                                 float ootfGain = pow(xyz.y / 1000.0, -0.2 / 1.2);
-                                return xyz * ootfGain / 203.0;
+                                return xyz * ootfGain / 264.96;
                             }
                         )");
                     break;
diff --git a/services/surfaceflinger/ScreenCaptureOutput.cpp b/services/surfaceflinger/ScreenCaptureOutput.cpp
index b70b53d05a..09dac23410 100644
--- a/services/surfaceflinger/ScreenCaptureOutput.cpp
+++ b/services/surfaceflinger/ScreenCaptureOutput.cpp
@@ -94,6 +94,16 @@ ScreenCaptureOutput::generateClientCompositionRequests(
         }
     }
 
+    if (outputDataspace == ui::Dataspace::BT2020_HLG) {
+        for (auto& layer : clientCompositionLayers) {
+            auto transfer = layer.sourceDataspace & ui::Dataspace::TRANSFER_MASK;
+            if (transfer != static_cast<int32_t>(ui::Dataspace::TRANSFER_HLG) &&
+                transfer != static_cast<int32_t>(ui::Dataspace::TRANSFER_ST2084)) {
+                layer.whitePointNits *= (1000.0f / 203.0f);
+            }
+        }
+    }
+
     Rect sourceCrop = mRenderArea.getSourceCrop();
     compositionengine::LayerFE::LayerSettings fillLayer;
     fillLayer.source.buffer.buffer = nullptr;