Unlike UWP, WindowsAppSdk does not support HDR composition

[benstevens48]

Describe the bug

In UWP, I can create a CompositionDrawingSurface with pixel format DirectXPixelFormat.R16G16B16A16Float and it then follows the rules of system composition for HDR: if Windows HDR display mode is enabled, then the content is passed to the system compositor, which uses a floating point format without scaling, and can display values outside [0,1]. Any SDR content rendered to the drawing surface should be scaled by the app by (the display's SDR white level) / 80 (in my case this is (240 / 80). However, it seems this is not supported in WindowsAppSDK. It seems the surface just undergoes a simple scRGB to sRGB color transform (basically just gamma correction) then is rendered as SDR. I am wondering if this is because WindowsAppSDK is composing to an 8-bit swap chain?

Getting this supported is critical for me to migrate my photo-viewing app. In HDR mode, WindowsAppSDK should use a 16-bit floating point swap chain. SDR content should be scaled by (the display's SDR white level) / 80 when rendered to it and 16-bit composition surfaces should be rendered unchanged.

Steps to reproduce the bug

The following outputs look identical in HDR mode, when in fact the HDR-rendered version should (a) produce a brighter than SDR brightest rectangle and (b) otherwise be darker, assuming the display's SDR white level is set to > 80 nits, because the code below doesn't allow for the display's SDR white level.

 public sealed partial class MainWindow : Window {
     public MainWindow() {
         InitializeComponent();
     }

     Size surfaceSize = new Size(200, 50);

     private void renderHdrButton_Click(object sender, RoutedEventArgs e) {
         var rawPixelsPerViewPixel = renderHdrButton.XamlRoot.RasterizationScale;
         try {
             var pixelSize = new Size(Math.Round(surfaceSize.Width * rawPixelsPerViewPixel), Math.Round(surfaceSize.Height * rawPixelsPerViewPixel));
             var compositor = this.Compositor;
             var device = CanvasDevice.GetSharedDevice();
             var compositionDevice = CanvasComposition.CreateCompositionGraphicsDevice(compositor, device);
             var drawingVisualSurface = compositionDevice.CreateDrawingSurface(pixelSize, Microsoft.Graphics.DirectX.DirectXPixelFormat.R16G16B16A16Float, Microsoft.Graphics.DirectX.DirectXAlphaMode.Premultiplied);
             var drawingVisualSurfaceBrush = compositor.CreateSurfaceBrush(drawingVisualSurface);
             drawingVisualSurfaceBrush.HorizontalAlignmentRatio = 0;
             drawingVisualSurfaceBrush.VerticalAlignmentRatio = 0;
             drawingVisualSurfaceBrush.Stretch = CompositionStretch.None;
             drawingVisualSurfaceBrush.Scale = new Vector2((float)(1.0 / rawPixelsPerViewPixel), (float)(1.0 / rawPixelsPerViewPixel));
             var drawingVisualSprite = compositor.CreateSpriteVisual();
             drawingVisualSprite.Size = surfaceSize.ToVector2();
             drawingVisualSprite.Brush = drawingVisualSurfaceBrush;
             ElementCompositionPreview.SetElementChildVisual(drawingVisualContainer, drawingVisualSprite);
             using (var ds = CanvasComposition.CreateDrawingSession(drawingVisualSurface)) {
                 ds.Clear(new Vector4(0, 0, 0, 1));
                 var correctedVal = (float)Math.Pow(0.5, 2.2); //Correct for gamma
                 ds.FillRectangle(new Rect(0, 0, 50, 50), CanvasSolidColorBrush.CreateHdr(device, new Vector4(correctedVal, correctedVal, correctedVal, 1)));
                 ds.FillRectangle(new Rect(50, 0, 50, 50), CanvasSolidColorBrush.CreateHdr(device, new Vector4(1, 1, 1, 1)));
                 ds.FillRectangle(new Rect(100,0, 50,50), CanvasSolidColorBrush.CreateHdr(device, new Vector4(5, 5, 5, 1)));
             }
         } catch (Exception) {
         }
     }

     private void renderSdrButton_Click(object sender, RoutedEventArgs e) {
         var rawPixelsPerViewPixel = renderHdrButton.XamlRoot.RasterizationScale;
         try {
             var pixelSize = new Size(Math.Round(surfaceSize.Width * rawPixelsPerViewPixel), Math.Round(surfaceSize.Height * rawPixelsPerViewPixel));
             var compositor = this.Compositor;
             var device = CanvasDevice.GetSharedDevice();
             var compositionDevice = CanvasComposition.CreateCompositionGraphicsDevice(compositor, device);
             var drawingVisualSurface = compositionDevice.CreateDrawingSurface(pixelSize, Microsoft.Graphics.DirectX.DirectXPixelFormat.B8G8R8A8UIntNormalized, Microsoft.Graphics.DirectX.DirectXAlphaMode.Premultiplied);
             var drawingVisualSurfaceBrush = compositor.CreateSurfaceBrush(drawingVisualSurface);
             drawingVisualSurfaceBrush.HorizontalAlignmentRatio = 0;
             drawingVisualSurfaceBrush.VerticalAlignmentRatio = 0;
             drawingVisualSurfaceBrush.Stretch = CompositionStretch.None;
             drawingVisualSurfaceBrush.Scale = new Vector2((float)(1.0 / rawPixelsPerViewPixel), (float)(1.0 / rawPixelsPerViewPixel));
             var drawingVisualSprite = compositor.CreateSpriteVisual();
             drawingVisualSprite.Size = surfaceSize.ToVector2();
             drawingVisualSprite.Brush = drawingVisualSurfaceBrush;
             ElementCompositionPreview.SetElementChildVisual(drawingVisualContainerSdr, drawingVisualSprite);
             using (var ds = CanvasComposition.CreateDrawingSession(drawingVisualSurface)) {
                 ds.Clear(new Vector4(0, 0, 0, 1));
                 ds.FillRectangle(new Rect(0, 0, 50, 50), CanvasSolidColorBrush.CreateHdr(device, new Vector4(0.5f, 0.5f, 0.5f, 1)));
                 ds.FillRectangle(new Rect(50, 0, 50, 50), CanvasSolidColorBrush.CreateHdr(device, new Vector4(1, 1, 1, 1)));
                 ds.FillRectangle(new Rect(100, 0, 50, 50), CanvasSolidColorBrush.CreateHdr(device, new Vector4(5, 5, 5, 1)));
             }
         } catch (Exception) {
         }
     }
 }

Expected behavior

No response

Screenshots

No response

NuGet package version

Windows App SDK 1.8.5: 1.8.260209005

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 24H2 (26100, June 2025 Update)

IDE

No response

Additional context

No response

[lauren-ciha]

Thank you for your feedback! We're tracking this proposal on the WinUI repository: microsoft/microsoft-ui-xaml#67. Feel free to follow there for more updates.

[benstevens48]

@lauren-ciha That issue was about UWP as well (I think the poster maybe hadn't used CompositionDrawingSurface with floating point format correctly). What I'm referring to is a regression from UWP.

[lauren-ciha]

WinUI 3, the UI layer for Windows App SDK, does not have full HDR support at this time. Resolving this issue would be a part of the feature request in #67. Therefore, we are keeping this issue closed as a duplicate. Please add your issue description to the conversation in the WinUI repo, where the teams that own CompositionDrawingSurface can take a closer look.