Add depth buffer option

[joseyose]

Right now in the example you are only rendering a triangle so there's no need for a depth buffer, but as soon you try to integrate this in application that is depth testing the ui will not draw correctly.

[cohaereo]

Closed this on accident, sorry for that.

I thought that EGUI wouldn't need a depth buffer? I'm guessing they're not doing Z-sorting yet? I personally haven't had any problems with it, so if you could give an example of the lack of depth testing causing graphical issues, that would be great!

[joseyose]

No worries!
Here's the example included of just adding depth test and clearing both the color and depth buffer:

[cohaereo]

Did some testing myself, was able to reproduce that exact same issue.
I saw you already fixed this on your fork, if you can PR your changes I'll update the crate

[joseyose]

I need to do some more testing, but I'll try and do a PR if it's working as intended.