Recently got my theme working with the model-viewer and I'm very pleased with it aside from one small issue with the Shopify thumbnail system. Upon uploading a 3D model, Shopify auto-generates a series of JPG thumbnails with white backgrounds and these get fed into the product images in various places throughout the store. If I had chosen a lighter theme, this would not be much of an issue but unfortunately my theme is black, which causes a stark contrast when my products are shown due to my 3D model being the featured image. One solution would be to make it the 2nd image and have users select it as a workaround but that isn't exactly preferred. Ideally there would be an option somewhere to either generate thumbnails with transparency (ideally PNG format) or the ability to choose the background color the thumbnails get rendered with. I've been pulling my hair out trying to figure out a workaround and I've run out of ideas so hopefully I've just missed something!
Solved! Go to the solution
This is an accepted solution.
Actually, you can supply your own preview image for 3d models.
Can't quite get Shopify own tutorial on this, but here is one from a theme maker, check steps 1-6 there:
Basically, when you've uploaded your 3d model, click it to open preview and in the right-top corner of the screen, under 3-dot ("more options") there is a "replace thumbnail" where you can upload your own image.