GLTFExporter output file size regression

[elalish]

Describe the bug

Importing a glTF with jpeg textures and reexporting it is now causing a major bloat in file size compared to the original (~2.5x for DamagedHelmet). I'm pretty sure this is due to #23857, as we're now using the convertToBlob method of OffscreenCanvas instead of the toBlob method of Canvas. This feels like it might also be a Chrome bug? It is correctly outputting JPEGs of the proper dimensions, they are just much larger, like the quality setting is defaulting to something a lot higher than the usual 0.85. @donmccurdy @robertlong Thoughts? Our regression tests caught this in <model-viewer> when I tried to upgrade.

To Reproduce

Steps to reproduce the behavior:

1. Go to the model-viewer editor and select DamagedHelmet
2. Click on "Download Scene"
3. Open the zip and inspect DamagedHelmet.glb - note it is now 9.3MB

Expected behavior

The GLB should be ~4MB, similar to the 3.8MB original

Screenshots

If applicable, add screenshots to help explain your problem (drag and drop the image).

Platform:

• Device: Desktop
• OS: MacOS
• Browser: Chrome
• Three.js version: r140

[robertlong]

It does sound like a Chrome bug but I think the best option is to only use OffscreenCanvas when in a WebWorker context, avoiding this code path entirely for the vast majority of users. I'll work on a patch. Thanks for catching this! I did not notice the large file size regression.

[robertlong]

It looks like Blink has a default JPEG quality of 92% and default WebP quality of 80%. And yeah for some reason this default quality is not being used when using convertToBlob. I can go ahead and use those defaults for those mimetypes if that makes sense? OffscreenCanvas really is only supported in Blink-powered engines right now and those defaults seem like good defaults for us to use for now.

[robertlong]

With these default quality levels, I'm only seeing a 4 byte difference between the DamagedHelmet using Canvas.toBlob and OffscreenCanvas.convertToBlob. Not sure where the 4 bytes are being reduced 🤔 but I'd put that as acceptable.

[robertlong]

I've made a patch available here #23998

[elalish]

Have you filed this issue on Chrome?