Make the occlusion culling debug draw mode draw a translucent overlay

[Calinou]

This allows for easy, depth-aware navigation in the 3D editor while being able to view which meshes are occluders and which meshes aren't.

I've tested this change with both Forward+ and Mobile rendering methods. No Vulkan validation errors are reported when running with --gpu-validation on either rendering method. (The Compatibility rendering method currently doesn't support most debug draw modes, including the occlusion culling buffer. Occlusion culling itself does work though.)

Thanks @myaaaaaaaaa for the help 🙂

Testing project: test_occlusion_culling_buffer.zip

• This closes Make the occlusion culling debug draw mode display a translucent overlay instead of replacing the viewport godot-proposals#2911.

Preview

The two cubes in the front have occluders, while the cube in the back doesn't.

[BlueCube3310]

I think this is a useful change, especially since the jittered buffer makes it very difficult to see the shapes of the objects. Needs a rebase though

[Calinou]

Rebased and tested again, it works as expected.

The "vignette" effect is also gone (it was already fixed in master). I've updated the screenshot in OP accordingly.

[BlueCube3310]

Looks good to me, I tested it on several scenes with many meshes and it works correctly. Additionally it makes it easier to notice how the occluders interact with the scene

[clayjohn]

This should just be a flag otherwise we are increasing load times for no reason

[Calinou]

I've pushed a second commit to attempt this, but it doesn't seem to work on my end (it just renders as it did before).

[BlueCube3310]

This should probably be

Suggested change

	copy.push_constant.flags |= COPY_TO_FB_FLAG_OCCLUSION_CULLING_BUFFER;
	copy_to_fb.push_constant.flags |= COPY_TO_FB_FLAG_OCCLUSION_CULLING_BUFFER;

[Calinou]

Thanks 🙂 I've tried this but now I just see a fully opaque red viewport when the debug draw mode is enabled. So there's still an issue somewhere else.

[BlueCube3310]

The correct pipeline is never applied since it relies on the "COPY_TO_FB_OCCLUSION_CULLING_BUFFER" mode that doesn't get used now