Metal: after experimenting with EDR tone-mapping, it's here but disabled. It's unclear how best to render content from Windows. We get the system calibration peak nits in the Mastering Display Color Volume metadata, but this won't apply to most content.

VoidLink/Metal/MetalVideoRenderer.m

@@ -94,6 +94,12 @@ struct Vertex {
 
 static const NSUInteger MaxFramesInFlight = 3;
 
+// EDR tone-mapping is possible but it's unclear how
+// best to tone-map Windows content
+static BOOL useEDR = NO;
+
+CFStringRef __currentColorSpace;
+
 @implementation MetalVideoRenderer {
     dispatch_queue_t _sq;
     id<MTLDevice> _device;
@@ -106,7 +112,7 @@ static const NSUInteger MaxFramesInFlight = 3;
     CVMetalTextureCacheRef _textureCache;
     CVMetalTextureRef _cvMetalTextures[MAX_VIDEO_PLANES];
 
-    CGFloat _currentEDRHeadroom;
+    float _currentEDRHeadroom;
     int _lastColorSpace;
     BOOL _lastFullRange;
     size_t _lastFrameWidth;
@@ -166,6 +172,9 @@ static const NSUInteger MaxFramesInFlight = 3;
     if (_renderPassDescriptor) {
         _renderPassDescriptor = nil;
     }
+    if (__currentColorSpace) {
+        CFRelease(__currentColorSpace);
+    }
 }
 
 #if !TARGET_OS_TV
@@ -192,7 +201,7 @@ static const NSUInteger MaxFramesInFlight = 3;
 #endif
     if (headroom != _currentEDRHeadroom) {
         Log(LOG_I, @"EDR headroom changed to %.1f", headroom);
-        _currentEDRHeadroom = headroom;
+        _currentEDRHeadroom = (float)headroom;
     }
 }
 
@@ -232,11 +241,15 @@ static const NSUInteger MaxFramesInFlight = 3;
         CFDataRef masteringDisplayColorVolume = CVBufferCopyAttachment(frame.pixelBuffer, kCVImageBufferMasteringDisplayColorVolumeKey, nil);
         CFDataRef contentLightLevel = CVBufferCopyAttachment(frame.pixelBuffer, kCVImageBufferContentLightLevelInfoKey, nil);
         if (masteringDisplayColorVolume) {
+            // This tone-mapper does receive the host's max nits in MDCV when connecting to Windows,
+            // but I think using this for tone-mapping would break apps not using system calibration (most apps).
             layer.EDRMetadata = [CAEDRMetadata HDR10MetadataWithDisplayInfo:(__bridge NSData *)masteringDisplayColorVolume
                                                                 contentInfo:contentLightLevel ? (__bridge NSData *)contentLightLevel : nil
                                                          opticalOutputScale:100.0f];
         } else {
-            layer.EDRMetadata = [CAEDRMetadata HDR10MetadataWithMinLuminance:0.005f maxLuminance:1000.0f opticalOutputScale:100.0f];
+            layer.EDRMetadata = [CAEDRMetadata HDR10MetadataWithMinLuminance:0.005f
+                                                                maxLuminance:1000.0f
+                                                          opticalOutputScale:100.0f];
         }
         LogOnce(LOG_I, @"EDRMetadata set to colorspace %@, transfer function %@, %@", layer.colorspace, frame_trc, layer.EDRMetadata);
     });
@@ -328,21 +341,31 @@ static const NSUInteger MaxFramesInFlight = 3;
                                                                        : [NSString stringWithFormat:@"Unknown: %lu", (unsigned long)layer.pixelFormat]);
             }
 
-            if ([CAEDRMetadata isAvailable]) {
+#if TARGET_OS_TV
+            // These can only be changed on the main thread
+            dispatch_sync(dispatch_get_main_queue(), ^{
+                layer.colorspace = newColorSpace;
+                layer.pixelFormat = newPixelFormat;
+            });
+#else
+            if (useEDR && [CAEDRMetadata isAvailable]) {
                 [self applyEDRFromFrame:frame withColorspace:colorspace toLayer:layer];
             } else {
                 // These can only be changed on the main thread
                 dispatch_sync(dispatch_get_main_queue(), ^{
-#if !TARGET_OS_TV
                     if (isHDR) {
                         layer.wantsExtendedDynamicRangeContent = YES;
                     }
-#endif
                     layer.colorspace = newColorSpace;
                     layer.pixelFormat = newPixelFormat;
                 });
-                CGColorSpaceRelease(newColorSpace);
             }
+#endif
+            if (__currentColorSpace) {
+                CFRelease(__currentColorSpace);
+            }
+            __currentColorSpace = CGColorSpaceCopyName(newColorSpace);
+            CGColorSpaceRelease(newColorSpace);
         }
 
         // Create the new colorspace parameter buffer for our fragment shader
@@ -548,13 +571,12 @@ static const NSUInteger MaxFramesInFlight = 3;
             [renderEncoder setFragmentTexture:CVMetalTextureGetTexture(_cvMetalTextures[i]) atIndex:i];
         }
 
-//        if (layer.pixelFormat == MTLPixelFormatRGBA16Float) {
-//            [self pollCurrentEDRHeadroom];
-//            [renderEncoder setFragmentBytes:&_currentEDRHeadroom length:sizeof(CGFloat) atIndex:0];
-//        }
-
         [renderEncoder setVertexBuffer:_VideoVertexBuffer offset:0 atIndex:0];
         [renderEncoder setFragmentBuffer:_CscParamsBuffer offset:0 atIndex:0];
+        if (layer.pixelFormat == MTLPixelFormatRGBA16Float) {
+            [self pollCurrentEDRHeadroom];
+            [renderEncoder setFragmentBytes:&_currentEDRHeadroom length:sizeof(float) atIndex:1];
+        }
         [renderEncoder drawPrimitives:MTLPrimitiveTypeTriangleStrip vertexStart:0 vertexCount:4];
         [renderEncoder endEncoding];
 
@@ -628,4 +650,11 @@ static const NSUInteger MaxFramesInFlight = 3;
 - (void)resize:(CGSize)size {
 }
 
++ (NSString *)currentColorSpace {
+    if (__currentColorSpace) {
+        return (__bridge NSString *)__currentColorSpace;
+    }
+    return nil;
+}
+
 @end