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Index problems in some projects

Hi guys, any idea why some of the projects are having these issues? (see images).

I did a frame capture and it seems that one of the triangle indices is a crazy huge number. Possibly a problem loading the obj file? This only seems to happen on the macOS target. The iOS target doesn’t show the problem.


Hi @knight556

Please could I have some more details:

Is this the latest edition of Metal by Tutorials (v2)?

Does this happen on provided sample code?

What version of macOS and Xcode are you running?

What is your hardware?


  • Yes this is the very latest edition of the book
  • Yes this happens with the sample code
  • macOS 10.15 and Xcode 11.1 (no betas)
  • MacBook Pro 13" 2018

@knight556 - It’s an interesting problem, thank you for bringing it to our attention :slight_smile:.

Thanks to @mhorga, I’ve been able to reproduce the problem on my MacBook Pro, by running on my Intel GPU, rather than my AMD one. Your MacBook only has the integrated Intel GPU, I believe.

I’ve been testing on the Chapter 9 Scene Graph scene, and it appears to be only the ground plane that’s causing the problem. I don’t know why, for the moment, but it works when I replace the ground plane with a large flattened box.

I’ll attach that here, so that you can use it in place of the ground plane, and we’ll continue to examine the problem and see why. (1.4 KB)

Hi @caroline, any new information about this problem?

@knight556 - all I can speculate is that it must be some oddity with the Intel chip where it needs more geometry on the plane. I actually tried that before and it didn’t work, but I used Blender, which might have produced a different output.

This is an export from Houdini which works for me. (995 Bytes)

Check it and make sure it works for you.

If it does, take a look at the file in TextEdit and compare it to the other one. There’s not a lot of difference, so I can’t see why the Intel chip has difficulty.

@caroline Is this something that needs to be reported to Apple? Seems like a bug.

Yes, it does seem like a bug.

@caroline Are you able to report this to Apple? Would be great to see it resolved :grinning:

I’ll take another look at it in a couple of weeks, as I’m preparing to go to SIGGRAPH Asia :dancer: next week, and it always takes me ages to put together a project for bug reporting.