Gate LTC LUTs behind a feature and merge them to a texture array by beicause · Pull Request #24065 · bevyengine/bevy

beicause · 2026-05-02T00:29:32Z

Objective

Alternative to #24004.

#23288 adds ltc luts for rect light support which implicitly requires bevy_image/ktx2 and bevy_image/zstd otherwise loading ltc luts will panic.

We either accept to always enable area light supoort (#24004), or add a feature to opt out it (this PR).

Solution

Gate ltc luts behind a feature and merge them to a texture array.

Testing

rect_light example works.

github-actions · 2026-05-02T00:37:52Z

Your PR caused a change in the graphical output of an example or rendering test. This might be intentional, but it could also mean that something broke!
You can review it at https://pixel-eagle.com/project/B04F67C0-C054-4A6F-92EC-F599FEC2FD1D?filter=PR-24065

If it's expected, please add the M-Deliberate-Rendering-Change label.

If this change seems unrelated to your PR, you can consider updating your PR to target the latest main branch, either by rebasing or merging main into it.

github-actions · 2026-05-02T00:45:38Z

Your PR caused a change in the graphical output of an example or rendering test. This might be intentional, but it could also mean that something broke!
You can review it at https://pixel-eagle.com/project/B04F67C0-C054-4A6F-92EC-F599FEC2FD1D?filter=PR-24065

If it's expected, please add the M-Deliberate-Rendering-Change label.

If this change seems unrelated to your PR, you can consider updating your PR to target the latest main branch, either by rebasing or merging main into it.

JMS55 · 2026-05-02T01:01:26Z

Please make sure the new lut passes ktx validate: #23900

kfc35 · 2026-05-02T01:15:54Z

This PR makes progress on #23975, so I’ll add it to the milestone for expedited consideration

With this, the deferred_rendering example works for 1) Deferred and 2) Forward, but 3) Forward + Prepass doesn’t work. I’ll add more detail in the GH issue.

JMS55 · 2026-05-02T01:51:56Z

I like this more than the other PR.

Maybe we should rename the feature to "rect_lights" or something though? Idk

beicause · 2026-05-02T01:55:00Z

I like this more than the other PR.

Maybe we should rename the feature to "rect_lights" or something though? Idk

PointLight may use ltc luts too #23400

JMS55 · 2026-05-02T01:57:53Z

Ahh right, nvm.

JMS55 · 2026-05-02T01:58:33Z

How about "area_lights"?

beicause · 2026-05-02T02:06:18Z

How about "area_lights"?

"area_lights" sounds like we should gate the RectLight code as well. How about "area_light_luts"?

JMS55 · 2026-05-02T02:08:49Z

"area_lights" sounds like we should gate the RectLight code as well

Why not do that? They need the LUTs to function, no?

beicause · 2026-05-02T02:24:30Z

"area_lights" sounds like we should gate the RectLight code as well

Why not do that? They need the LUTs to function, no?

I'm not sure about this, it would add complexity. We didn't do it for tonemapping_luts either.

kfc35

Checked out the branch and everything looks the same wrt RectLights. Did not find any issues in the code. As I have also mentioned, it also allows the deferred_rendering example to run too!

I just have a (long) non-blocking comment about requiring the feature for the testbed.

kfc35 · 2026-05-02T14:57:33Z

 name = "testbed_3d"
 path = "examples/testbed/3d.rs"
 doc-scrape-examples = true
+required-features = ["area_light_luts"]


non-blocking comment: I know that I recently added a rect_light to the lights scene, but I don’t know if this should necessarily be added as a required feature in Cargo.toml, similar to how the ui testbed doesnt require the debug ui feature flag. The ui testbed doesn’t insert the debug outline scene if the feature isn’t enabled. Perhaps something similar should be done for the 3d testbed? It’ll allow the 3d testbed to keep growing in feature complexity without needing to specify a growing list of required flags.

A related question is, do we expect the app to fail loudly if the app creator adds a RectLight, but did not enable the associated feature? If the answer is no, then I think I wouldn’t require the feature here. I also then wouldn’t do any feature gating of the RectLight in the testbed so that case could theoretically be tested.

I agree that it should be added in example-run.yml though, which you have done. I also would still require it for the rect_light example as well

Co-authored-by: Kevin Chen <chen.kevin.f@gmail.com>

JMS55 · 2026-05-03T14:09:34Z

One comment: Is there somewhere we can error_once! log if area lights are used without the feature being enabled?

alice-i-cecile · 2026-05-03T17:57:30Z

One comment: Is there somewhere we can error_once! log if area lights are used without the feature being enabled?

Blocking on this :) Looks good otherwise.

@beicause

…s to `DownlevelFlags(INDEPENDENT_BLEND)` (bevyengine#24067) # Objective - Help out with bevyengine#23975 - Fixes an issue on WebGL2 as a result of bevyengine#23629 - Supporting bevyengine#23975 on WebGL2 necessitates fixing the “Forward + Prepass” option on the `deferred_rendering` example. The WebGPU focused solution to bevyengine#23629 requires this PR to also allow the “Forward + Prepass” option to work. ## Solution - @beicause mentioned gating the whole pipeline of `background_motion_vectors.rs` to `DownlevelFlags(INDEPENDENT_BLEND)` as implied in the error message in [this issue comment](bevyengine#23975 (comment)). It works! ## Testing - Included the change from this PR on top of bevyengine#24065, and it fixes the `deferred_rendering` example on WebGL2.

JMS55 · 2026-05-04T03:28:37Z

Use error_once!().

beicause · 2026-05-04T03:34:28Z

The code later in this file also uses Local<bool>, I think it's slightly faster than once.

Users can potentially insert in their own AreaLightLuts (though it's uncommon).

…yengine#24065) # Objective Alternative to bevyengine#24004. bevyengine#23288 adds ltc luts for rect light support which implicitly requires `bevy_image/ktx2` and `bevy_image/zstd` otherwise loading ltc luts will panic. We either accept to always enable area light supoort (bevyengine#24004), or add a feature to opt out it (this PR). ## Solution Gate ltc luts behind a feature and merge them to a texture array. ## Testing `rect_light` example works. --------- Co-authored-by: Kevin Chen <chen.kevin.f@gmail.com>

beicause added 3 commits May 2, 2026 07:59

Gate ltc luts behind a feature and merge them to a texture array

75a1596

Add required feature to rect_light example

7361cc0

CI

a85c48c

testbed_3d requires ltc_luts

2a4bb58

beicause force-pushed the feature-gate-ltc branch from 57c1f35 to 2a4bb58 Compare May 2, 2026 00:44

kfc35 added A-Rendering Drawing game state to the screen S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels May 2, 2026

github-project-automation Bot added this to Rendering May 2, 2026

github-project-automation Bot moved this to Needs SME Triage in Rendering May 2, 2026

beicause mentioned this pull request May 2, 2026

Merge LTC and DFG LUTs into a texture array #24004

Closed

kfc35 added this to the 0.19 milestone May 2, 2026

kfc35 mentioned this pull request May 2, 2026

Deferred rendering example fails on WebGL2 #23975

Closed

kfc35 added the D-Modest A "normal" level of difficulty; suitable for simple features or challenging fixes label May 2, 2026

kfc35 added D-Straightforward Simple bug fixes and API improvements, docs, test and examples and removed D-Modest A "normal" level of difficulty; suitable for simple features or challenging fixes labels May 2, 2026

Merge remote-tracking branch 'upstream/main' into feature-gate-ltc

b7d3c47

kfc35 mentioned this pull request May 2, 2026

Fix(bg motion vectors): gate BackgroundMotionVectorsPlugin pipelines to DownlevelFlags(INDEPENDENT_BLEND) #24067

Merged

beicause added 2 commits May 2, 2026 11:28

Rename ltc_luts to area_light_luts

611b067

fmt

14ed41d

kfc35 approved these changes May 2, 2026

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beicause and others added 2 commits May 2, 2026 23:40

Apply suggestions from code review

05f593d

Co-authored-by: Kevin Chen <chen.kevin.f@gmail.com>

update docs

8172984

JMS55 approved these changes May 3, 2026

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JMS55 added S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it and removed S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels May 3, 2026

alice-i-cecile added S-Waiting-on-Author The author needs to make changes or address concerns before this can be merged and removed S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it labels May 3, 2026

beicause added 2 commits May 4, 2026 11:07

Merge remote-tracking branch 'upstream/main' into feature-gate-ltc

31d2a9b

warn if rect light is used without area_light_luts feature

97e1d00

alice-i-cecile added S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it and removed S-Waiting-on-Author The author needs to make changes or address concerns before this can be merged labels May 4, 2026

alice-i-cecile enabled auto-merge May 4, 2026 03:41

alice-i-cecile added this pull request to the merge queue May 4, 2026

Merged via the queue into bevyengine:main with commit 0ff7c35 May 4, 2026
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github-project-automation Bot moved this from Needs SME Triage to Done in Rendering May 4, 2026

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beicause commented May 2, 2026

Objective

Solution

Testing

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