Make sure prepass notices changes in alpha mode

[eero-lehtinen]

Objective

Fixes #19150

Solution

Normally the validate_cached_entity in

bevy/crates/bevy_pbr/src/prepass/mod.rs

Lines 1109 to 1126 in 86cc02d

	let Some((current_change_tick, pipeline_id)) =
	view_specialized_material_pipeline_cache.get(visible_entity)
	else {
	continue;
	};
	// Skip the entity if it's cached in a bin and up to date.
	if opaque_phase.as_mut().is_some_and(|phase| {
	phase.validate_cached_entity(*visible_entity, *current_change_tick)
	}) || alpha_mask_phase.as_mut().is_some_and(|phase| {
	phase.validate_cached_entity(*visible_entity, *current_change_tick)
	}) || opaque_deferred_phase.as_mut().is_some_and(|phase| {
	phase.validate_cached_entity(*visible_entity, *current_change_tick)
	}) || alpha_mask_deferred_phase.as_mut().is_some_and(|phase| {
	phase.validate_cached_entity(*visible_entity, *current_change_tick)
	}) {
	continue;
	}

marks unchanged entites as clean, which makes them remain in the phase.

If a material is changed to an alpha_mode that isn't supposed to be added to the prepass pipeline, the specialization system just continues and doesn't indicate to the cache that the entity is not clean anymore.

I made these invalid entities get removed from the pipeline cache so that they are correctly not marked clean and then removed from the phase.

Testing

Tested with the example code from the issue.

[eero-lehtinen]

It also seems bad that we are doing all these material and mesh lookups for alpha blended materials every frame just to ignore them. Maybe this check could be moved to be a bit earlier at least.

[tychedelia]

Really good catch, thanks!