rend3-egui image buttons do not use the alpha channel

[John-Nagle]

It looks like the Rend3->egui integration sends textures to wgpu with settings that don't use the alpha channel. Run the Rend3 example egui to test. The Rust logo in the corner is supposed to have a transparent background, but does not.

As far as I can tell, this is not a consequence of settings at the egui API level. I've tried setting widget background color to transparent and such. But I could be wrong.

Not high priority.

[John-Nagle]

Possibly related WGPU issue: https://www.reddit.com/gallery/wu8uln