OBJ loader doesn't handle negative vertex indices

[avinxshKD]

Increasing access

Increasing access
Allows properly loading OBJ files that use negative indices (standard OBJ format feature).

Most appropriate sub-area of p5.js?

• WebGL

Feature enhancement details
The OBJ loader has a TODO about not supporting negative vertex indices, which are actually pretty common in OBJ files.

In src/webgl/loading.js around line 615:
// TODO: Faces can technically use negative numbers to refer to the

Most appropriate sub-area of p5.js?

• Accessibility
• Color
• Core/Environment/Rendering
• Data
• DOM
• Events
• Image
• IO
• Math
• Typography
• Utilities
• WebGL
• Build process
• Unit testing
• Internationalization
• Friendly errors
• Other (specify if possible)

Feature enhancement details

In the OBJ format, negative numbers count backwards from the most recent vertex. So -1 means the last vertex that was defined, -2 means second-to-last, etc. A lot of modeling software uses this.

Right now p5.js either ignores these or handles them incorrectly, which can mess up how models look when loaded.

Should be fixable by converting negative indices to positive ones based on the current vertex count (like vertexCount + negativeIndex + 1).

[welcome]

Welcome! 👋 Thanks for opening your first issue here! And to ensure the community is able to respond to your issue, please make sure to fill out the inputs in the issue forms.

For guidance on contributing, check out our contributing guidelines and other resources for contributors.
💬 If you have questions or need support, feel free to join the Processing Foundation Forum or visit our Community page.
📜 Please also review our Code of Conduct to understand our community standards.
Thank You!

[avinxshKD]

@davepagurek @perminder-17 Pls do let me know if im mistaken or did not taken care of smthg, thanks

[davepagurek]

Good catch, that's in the spec on Wikipedia too, TIL! https://en.wikipedia.org/wiki/Wavefront_.obj_file#Vertex_indices Possibly in implementation we can switch to using .at(-1) (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/at) instead of square bracket array indices to help with that.