Widget Compositing

The UI renderer already needs its own specific UI shader because we do shape clipping. So why not generalize this support for shaders into allowing widgets to do fancy things with them? Imagine how much more artistic Socially Distant's bloom effect would feel if we could apply it selectively where and when it makes sense. This would also make background blur effects much less janky to implement.

Widget compositing would allow you to write your own UI shader and assign it as a material to a widget. That widget, and children of it, would then be rendered using this custom UI material instead of the default one. If the material calls for it, the UI renderer will provide a texture that the material can sample from so one can apply effects to things behind a widget (think: blurring a background).

Since we already split widget meshes based on what texture is applied to them, it would be trivial to just use a material instance instead. This would allow a terminal emulator or syntax highlighter to render some text with a glow effect, and some without. This'd impact performance, but it'd be an artistic benefit in Socially Distant.