ClearColorConfig::None doesn't correctly disable clear behavior

[tychedelia]

Bevy version

0.13 (main branch).

What you did

Configured a simple 3d scene with ClearColorConfig::None on the only camera.

What went wrong

The screen is cleared each frame, instead of persisting draws between updates.

Additional information

Likely stemming from changes in #10325.

0.12:
0.13:

[alice-i-cecile]

How severe is this, and can you work around it? Trying to assess if fixing this should block the release.

[rparrett]

Simple repro: modify the render_to_texture to use ClearColorConfig::None. The "inner brown cube" should be all smeary, but it is not.

[tychedelia]

@alice-i-cecile We're porting Nannou to Bevy (nannou-org/nannou#953), and this is pretty fundamental to supporting a Processing like "sketch" creative coding setup (i.e., where the user "sketches" on a canvas). We're just getting started and probably won't be 100% baked until closer 0.14, but we'd ideally like to be able to track a stable release during our development for previews rather than following main.

[james-j-obrien]

I make use of this for a similar feature to nannou. I don't believe there is a work around that doesn't come with some performance loss. The simplest I can think of is keeping last frame's texture around so you can bind it when rendering the next frame and sample it, but that is a non-trivial amount of code across both rust and wgsl and comes with a perf hit.