gltf-transform optimize removes uv1 attribute from geometry.

[subhankar-trisetra]

Here are the differences in the geometry attributes before and after optimization using gltf-transform.
Before:

After:
Notice the missing uv1 property form here

Command I used:

gltf-transform optimize without_compression.glb scene_opt.glb --compress draco --flatten false --join false --palette false --texture-compress auto

Is there a way to fix this?

UPDATE:

If we run each step separately, it seems to preserve the uv1 channel and the final output is 1mb greater than just running the optimize command e.g.:

gltf-transform dedup without_compression.glb scene_opt.glb
gltf-transform instance scene_opt.glb scene_opt.glb
gltf-transform weld scene_opt.glb scene_opt.glb
gltf-transform simplify scene_opt.glb scene_opt.glb
gltf-transform resample scene_opt.glb scene_opt.glb
gltf-transform prune scene_opt.glb scene_opt.glb
gltf-transform sparse scene_opt.glb scene_opt.glb
gltf-transform png scene_opt.glb scene_opt.glb
gltf-transform jpeg scene_opt.glb scene_opt.glb
gltf-transform draco scene_opt.glb scene_opt.glb

The issue that I'm majorly facing is: uv1 is essential for me to store the lightmap data, and necessary for lightmaps to get applied in threejs. uv0 channel is kept for the uvs.

UPDATE

Upon doing some digging, what I found is:

glTF-Transform/packages/cli/src/cli.ts

Lines 361 to 366 in 255b715

	prune({
	keepAttributes: false,
	keepIndices: false,
	keepLeaves: false,
	keepSolidTextures: false,
	}),

And I believe the keepAttributes: false property in prune function is responsible for removing the uv1 attributes. Correct me if I'm wrong over here.

[donmccurdy]

Hi @subhankar-trisetra! You're correct that the keepAttributes: false option is responsible for removing UVs (and other vertex attributes) that are unused in the given file. Currently the optimize CLI command doesn't expose that as a flag. If you're doing this programmatically in a script you can of course choose whichever options, or I'd be open to PRs adding this flag to the optmize CLI command.

[subhankar-trisetra]

Hi @donmccurdy As I'm putting up the PR, just wanted to know what would be the correct way to accept the params for the prune function, using a stringified JSON as an argument or separate arguments for each params.
i.e. --prune-options '{"keepAttributes":false}' or --prune-attributes true --prune-indices false

[subhankar-trisetra]

Here's my PR: #1298

I went with option 2 for the above query. Please do let me know if anything needs to be changed.