Cold Specialization #17567
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Cold Specialization #17567
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tychedelia
added
A-Rendering
pcwalton
reviewed
Jan 27, 2025
| .render_lightmaps | ||
| .get(&entity) | ||
| .map(|lightmap| lightmap.slab_index); | ||
| self.shared.lightmap_slab_index = lightmap_slab_index; |
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Check pass ordering here. Are we sure that render_lightmaps is populated before this runs?
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Okay, will check. I also think that Lightmap needs to be added to the invalidation logic.
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Looks like we're good, as RenderLightmaps is populated during the extraction phase, and RenderMeshInstanceGpuBuilder::update is called during the collection subphase of the render phase.
alice-i-cecile
added
C-Performance
Closed
pcwalton
approved these changes
Jan 27, 2025
| .render_lightmaps | ||
| .get(&entity) | ||
| .map(|lightmap| lightmap.slab_index); | ||
| self.shared.lightmap_slab_index = lightmap_slab_index; |
There was a problem hiding this comment.
Looks like we're good, as RenderLightmaps is populated during the extraction phase, and RenderMeshInstanceGpuBuilder::update is called during the collection subphase of the render phase.
Co-authored-by: Patrick Walton <[email protected]>
Co-authored-by: Patrick Walton <[email protected]>
Co-authored-by: Patrick Walton <[email protected]>
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Cold Specialization
Objective
An ongoing part of our quest to retain everything in the render world, cold-specialization aims to cache pipeline specialization so that pipeline IDs can be recomputed only when necessary, rather than every frame. This approach reduces redundant work in stable scenes, while still accommodating scenarios in which materials, views, or visibility might change, as well as unlocking future optimization work like retaining render bins.
Solution
Queue systems are split into a specialization system and queue system, the former of which only runs when necessary to compute a new pipeline id. Pipelines are invalidated using a combination of change detection and ECS ticks.
The difficulty with change detection
Detecting “what changed” can be tricky because pipeline specialization depends not only on the entity’s components (e.g., mesh, material, etc.) but also on which view (camera) it is rendering in. In other words, the cache key for a given pipeline id is a view entity/render entity pair. As such, it's not sufficient simply to react to change detection in order to specialize -- an entity could currently be out of view or could be rendered in the future in camera that is currently disabled or hasn't spawned yet.
Why ticks?
Ticks allow us to ensure correctness by allowing us to compare the last time a view or entity was updated compared to the cached pipeline id. This ensures that even if an entity was out of view or has never been seen in a given camera before we can still correctly determine whether it needs to be re-specialized or not.
Testing
TODO: Tested a bunch of different examples, need to test more.
Migration Guide
TODO
AssetEventshas been moved into thePostUpdateschedule.