I have a set of thin layers with fine holes in them. At most angles these are rendering badly, with a mess of lines all over the surface. I can post the file, is anyone else seeing the same issue?
problem.skp (1.5 MB)
That’s not a bug. You are seeing what is known as Z-fighting. The faces are so close together the graphics card is unable to determine which one is in front of which. It’s an OpenGL thing.
The top component is 0.05 mm thick. When you zoom out so you can see the whole 5 meter square thing, that top component might as well have zero thickness.
I deleted the bottom face of the yellow component and moved it up by 2 mm and the Z-fighting goes away.
Ah, thanks for that diagnosis. Yikes, I already distorted the real object to be too thick, and not broad enough. Darn. I will need to add more distortion, unfortunately.
WIth 24 bit precision (16 million) on a Float32 I was not expecting a 100,000 ratio to hit this limit. I guess the calculations need more margin.
The z-fighting issue arises because computer graphic systems use a process of “z-buffering” to determine what is in front of what else. This process breaks the infinite range of distance from the camera into a collection of finite ranges and sorts geometry into the range bins for testing what is in front of what. The range bins use lower precision than the CPU and encounter situations in which two items fall in the same bin more often. The larger the depth range of the model and the farther away the camera is, the worse the problem becomes
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Thanks for the additional info about the z-buffering. Actually, I found the drawing is more reliable when the viewpoint moves further away. It is also much less likely to have artefacts when the viewpoint moves to straight-on or from the left. I’m guessing that the order objects are listed to OpenGL may be having some influence on precedence.