HDR Output

HDR_Output.md

HDR Output

This is an overview of HDR output support on different platforms.

DXGI

Windows 10 Creators Update added native HDR support to DXGI:

• must be enabled for display in Settings
• requires flip-mode swap chain

Detecting HDR

For any IDXGIOutput:

• obtain IDXGIOutput6
• use GetDesc1
• HDR color space will be:
  • RGB_FULL_G2084_NONE_P2020
• SDR color space will be:
  • RGB_FULL_G22_NONE_P709

Sample code:

IDXGIOutput6 *output6 = nullptr;
output->QueryInterface(&output6)
DXGI_OUTPUT_DESC1 oDesc;
output6->GetDesc1(&oDesc);

bool supportsHDR = (oDesc.ColorSpace == DXGI_COLOR_SPACE_RGB_FULL_G2084_NONE_P2020);

Display metadata

In DXGI_OUTPUT_DESC1:

• MinLuminance provides min luminance in nits
• MaxLuminance provides max luminance in nits, likely for just a small area of the display
• MaxFullFrameLuminance provides max luminance in nits that's valid for the entire display

IDXGIFactory1::IsCurrent can be called each frame to notify the app when display properties change.

Rendering

The recommended way to render HDR content is to use DXGI's RGB_FULL_G10_NONE_P709 color space with R16G16B16A16_FLOAT back buffer.

Do not use RGB10 for back buffers!

The color space RGB_FULL_G10_NONE_P709:

• linear sRGB with extended range = scRGB
• native composition format on Windows
• luminance is 80 nits for (1,1,1), so 1000 nits white is 12.5
• color primaries are Rec 709 / sRGB
• wide gamut supported via negative colors

How to use:

• obtain IDXGISwapChain3
• check support using CheckColorSpaceSupport
• set color space using SetColorSpace1

Never use SetHDRMetaData, obtain the range from DXGI_OUTPUT_DESC1 and tonemap to it.

References

https://learn.microsoft.com/en-us/windows/win32/direct3darticles/high-dynamic-range https://developer.nvidia.com/downloads/hdr-gdc-2018 https://www.asawicki.info/news_1703_programming_hdr_monitor_support_in_direct3d

macOS

macOS calls its HDR features EDR (extended dynamic range).

Detecting HDR

CAMetalLayer always supports EDR.

Dispay metadata

NSScreen provides two values:

• maximumPotentialExtendedDynamicRangeColorComponentValue should be used for checking the EDR capability of the display. If the value is 1.0, the display does not support EDR. If it's greater, the display supports EDR.
• maximumExtendedDynamicRangeColorComponentValue should be used after requesting EDR for tonemapping

The metadata corresponds directly to component values with (e.g. 100 nits = 1.0; 1000 nits = 10.0).

NSApplicationDidChangeScreenParametersNotification can be used to notify the app when the max component value changes.

Rendering

• use RGBA16Float format
• set metalLayer.wantsExtendedDynamicRangeContent on CAMetalLayer
• set color space to kCGColorSpaceExtendedLinearSRGB

Sample code:

CAMetalLayer *metalLayer = [CAMetalLayer new];
metalLayer.wantsExtendedDynamicRangeContent = YES;
metalLayer.pixelFormat = MTLPixelFormatRGBA16Float;
const CFStringRef name = kCGColorSpaceExtendedLinearSRGB;
CGColorSpaceRef colorspace = CGColorSpaceCreateWithName(name);
metalLayer.colorspace = colorspace;
CGColorSpaceRelease(colorspace);

References

https://developer.apple.com/documentation/metal/hdr_content/displaying_hdr_content_in_a_metal_layer?language=objc https://developer.apple.com/documentation/metal/hdr_content/performing_your_own_tone_mapping?language=objc

Vulkan

It's a mess right now, can't document it properly. Use Vulkan only on Linux.