[Fix] GltfExporter correctly exports buffer views for non-interleaved vertex data

[mvaligursky]

• Previously, a non-interleaved vertex buffer was stored using a single buffer view, which is not correct according to specs, as there is no single stride that can be specified for elements using it.
• This stores a per element buffer view for non=interleaved vertex formats, and removes last validation errors.

Additionally, handling of unsupported textures is now handled without crashing (by ignoring them), for both gltf and usdz exporters.

[kungfooman]

I am running into validation errors for a scene like this:

Errors:

I figured that instead of pushing a new accessor all the time, you can first check if a similiar one already exists - and use that id:

The code under vertexFormat.elements.forEach((element, elementIndex) => {, it can be done like:

                        const compareAccessor = (a, b) => {
                            return a.bufferView == b.bufferView &&
                              a.byteOffset == b.byteOffset &&
                              a.componentType == b.componentType &&
                              a.type == b.type &&
                              a.count == b.count;
                          }
                        let idx = json.accessors.findIndex(_ => compareAccessor(_, accessor))
                        if (idx === -1) {
                            idx = json.accessors.push(accessor) - 1;
                        }

That gets rid of the accessor errors, but I have no time to test more right more... accessor min/max should probably also be compared.

[mvaligursky]

@kungfooman - thanks for the feedback, I fixed both issues.

[kungfooman]

Great work as always, I tested as far as I could and it works.

Only problem I have is the texture exporting code fails in SeeMore, because of a type issue. Instead of Texture#levels being some kind of image, it is actually a UInt8Array... and then it just crashes currently.

I wanted to fix it myself, but the size of the UInt8Array just doesn't make sense to me:

Apparently the texture size of that DDS is 1024x1024, but the length of the UInt8Array is 524.288. 1024*1024 is already 1.048.576🤔

[mvaligursky]

Great work as always, I tested as far as I could and it works.

Thanks! Much appreciate your testing and feedback!

Only problem I have is the texture exporting code fails in SeeMore,

I added code to ignore those for now, just to avoid the crash. Can be properly handled in a separate PR there is more work on textures / materials to be done.