Apparently, doing a full Draco compression does affect the indices. I tested it with a simple model earlier, and there, the indices remained the same. But with the attached model, they are modified. (It might magically depend on the complexity of the model…? And … the new indices appear to be stored something that resembles a sparse accessor (but is not) … I’d have to read more here…)
The original model has ~46.2 MB, and a small segment of it looks like this:
compressionLevel=0, the model has ~16.8 MB, and looks like this:
One can see that the topology is right, but with the lines are bit squiggly due to the quantization. The default quantiztation for the positions is 11 bits (the README currently says 14, but it’s 11 - that has to be fixed).
So I also tried it with 14 quantization bits for the positions, and this results in ~18 MB, looking like this:
At this perspective, that’s hardly distinguishable from the original one.
compressionLevel=1, it goes down to ~13.1 MB, but … the indices are messed up:
But… this might not be toooo surprising. (In fact, I found it surprising that the indices did not seem to change when I tested it with a simpler model…)
Of course, the linked PR is only a slight improvement, compared a full re-write of the (changed) indices (but… it only took a few minutes to implement it, so that’s OK I guess). But when setting
compressionLevel=0, it should now be possible to transport the outline extension through
gltf-pipeline Draco compression, and this still reduces the size considerably.
Attached is the one with
test13-draco-compressionLevel-0-14bit.glb (17.6 MB)