naituw/metaledr-ios

Demo of using Metal to render EDR / HDR content on iOS platform

MetalEDR-iOS

Demo of using Metal to render EDR/HDR content on iOS platform.

How it works

This demo uses a hack to activate EDR display on iOS platform:

• By setting up an invisible AVPlayerLayer, and plays short HDR video clip in the backgrond
• inspired by https://github.com/kiding/wanna-see-a-whiter-white

Then we can use Metal with a Float Point pixel format to output EDR contents.

Limitation

The "EDR trigger" hack basically has the same effect with metalLayer.wantsExtendedDynamicRangeContent = YES;,

But we still missing APIs like -[NSScreen maximumExtendedDynamicRangeColorComponentValue], so it's very hard to apply appropriate tone-mapping within Metal rendering process.

This demo outputs the raw pixel values loaded by CoreGraphics without applying any tone-mapping, so the colors will clip at current EDR max value and may seems off.

Credit

• Inspired by:
  • https://kidi.ng/wanna-see-a-whiter-white/
• HDR Video (EDR Trigger):
  • https://github.com/kiding/wanna-see-a-whiter-white
• HDR Image Resources:
  • https://github.com/AcademySoftwareFoundation/openexr-images/tree/master/TestImages
• Some sample code from:
  • https://developer.apple.com/wwdc21/10161
  • https://developer.apple.com/documentation/metal/using_a_render_pipeline_to_render_primitives?language=objc

metaledr-ios's Issues

Better workaround

Hey,

Thank you so much for sharing this demo!

I was playing a lot with this and found that there is an easier way to enable EDR on the MTKView:
The wantsExtendedDynamicRangeContent property is actually there on iOS as well, just not public. So you can just use KVO to enable EDR rendering:

[self.layer setValue:[NSNumber numberWithBool:YES] forKey:@"wantsExtendedDynamicRangeContent"];

No need to add a hidden AVPlayerLayer anymore. 🙂

Similarly, you can also query the EDR properties of the screen:

[[UIScreen mainScreen] valueForKey:@"extendedDynamicRangeCurrentHeadroom"];
[[UIScreen mainScreen] valueForKey:@"extendedDynamicRangePotentialHeadroom"];
[[UIScreen mainScreen] valueForKey:@"extendedDynamicRangeReferenceHeadroom"];

I hope that helps. Thanks again!

iOS 15.4

This technique no longer works on iOS 15.4 you need to set wantsExtendedDynamicRangeContent like mentioned in issue #1