Revert Screen Space Transmission Gate for Mesh Bind Groups

[kfc35]

Objective

• Alongside Fix: Add SyncComponents for SSAO, ensuring SSAOResources is synced #24086, helps with view bindgroup layout changes can cause crash #24084, although I think we should double check any other added conditionals for bind group entries to make sure they are accurate.

Solution

So, originally the SCREEN_SPACE_TRANSMISSION was enabled with key.intersects(MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_RESERVED_BITS). However, a low quality transmission would make this false, since low’s MeshPipelineKey is configured like this: const SCREEN_SPACE_SPECULAR_TRANSMISSION_LOW = 0 << Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_SHIFT_BITS;. So, a ScreenSpaceTransmission with Low Quality would break rendering (since another if-block merely checks that the ScreenSpaceTransmission component exists)

Making it so that the low transmission truly does not include the view_transmission_textures makes the transmission render not properly - the spheres disappear!

So, I think the proper fix here is to remove the gating around transmission textures.
Edit: Another potential fix is to change the condition of the intersects but I’m not sure how to encode what we want unless we want to add another bit for ScreenSpaceTransmission component exists essentially? Happy to close this PR if that is an acceptable direction.

Testing

cargo run --example transmission works for all quality levels.

[kfc35]

This screen space transmission issue is causing problems (and strobing!) with a couple other examples at least:
fog_volumes and meshlet

[beicause]

I can accept this since ScreenSpaceTransmission is a required component and enabled by default. We can add a way to disable it in a separate PR.

[JMS55]

Why not check all the bits for the different quality levels?

[kfc35]

If I understand your question and the code correctly, the quality level is encoded in 2 bits (for low, medium, high, and ultra), a low quality level is encoded as a 0, and we want SCREEN_SPACE_TRANSMISSION to be enabled in that scenario anyway (or else low quality just doesn’t render — I tested with the transmission example). Checking the bits for each individual quality would be redundant in that case since any combo of bits should result in screen space transmission being enabled, so I’m removing the useless gating.

I’m interpreting that you mean to check every individual quality level as already done so here:

bevy/crates/bevy_pbr/src/render/mesh.rs

Lines 3555 to 3567 in 5b1581d

	let blur_quality =
	key.intersection(MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_RESERVED_BITS);
	shader_defs.push(ShaderDefVal::Int(
	"SCREEN_SPACE_SPECULAR_TRANSMISSION_BLUR_TAPS".into(),
	match blur_quality {
	MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_LOW => 4,
	MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_MEDIUM => 8,
	MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_HIGH => 16,
	MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_ULTRA => 32,
	_ => unreachable!(), // Not possible, since the mask is 2 bits, and we've covered all 4 cases
	},
	));