Add support for creating glutin EGL displays on Windows using Angle

[tronical]

Angle provides libEGL.dll, which glutin loads. The only change necessary is to get the platform display via EGL_PLATFORM_ANGLE_ANGLE and treating it as a legacy display.

Fixes #1508

• Tested on all platforms changed
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality

[kchibisov]

Thanks.

It's sort of weird that Windows EGL was simply forgotten in the display creation, since I don't see any method touching RWHND for it...

[tronical]

I'll push fixes to the review comments as follow-up patches. In the event that this finds approval in the end, I'd squash them into one, if that's okay.

[kchibisov]

In addition, could you post the screenshot of default example running on ANGLE (want to see output of example), so I could see how it works, given that I can't test it.

[tronical]

Proof ;)

[kchibisov]

@tronical oh, could it work in qemu setup or only vmware specific? Or where you using gpu passthrough for that?

[tronical]

@tronical oh, could it work in qemu setup or only vmware specific? Or where you using gpu passthrough for that?

I'm using VMware's D3D drivers, those I think do pass-through to some extent. But in principle this should work absolutely anywhere, as D3D comes with the WARP software renderer. I think/hope that Angle falls back to selecting that if no other was found. Otherwise the angle extensions also allow to explicitly select a warp D3D device. This could be an interesting glutin API extension in the future.

Toolkits that use Warp often have some environment variable that allows users to explicitly opt into using warp.

[kchibisov]

Looks good after cargo +nightly fmt.

[tronical]

Formatting fixed and squashed.

[kchibisov]

Thanks!