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> Use of float makes it unlikely that you’d run it on the PlayStation, which has no FPU.

I think this sentence just made me realize what made the PSX graphics look so "PSX", I'm guessing all the positions/translations and similar stuff were actually not floating point which they typically are (today at least), hence the classic look of triangles/meshes kind of "jumping"? Huh...

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The jumpy polygons are because the PSX's GPU only accepts vertex positions in screen coordinates, meaning that vertices always snap to hard integer values. There is no sub-pixel accuracy. That's not a limitation caused by the PSX's lack of an FPU though. A large part of the render pipeline and standard libraries are built around the use of fixed point math, i.e. using integers to simulate decimal values. The GTE co-processor which handles 3D math makes use of standardized fixed-point types. So the PSX would have been capable of calculating sub-pixel coordinate values, it's just that the communication between CPU and GPU was designed to use only integer screen coordinate values.

It's slightly more complicated than that. The PlayStation's geometry pipeline uses fixed-point coordinates with a decent amount of fractional precision (12 bits), however the GPU lacks support for subpixel rendering and operates entirely in screen space using integer X/Y pixel coordinates; all transformed vertices thus have to be rounded CPU-side before they reach the GPU. The GPU is also a 2D rasterizer only, with no perspective correction nor depth buffering, so transformed Z values are used on the CPU to sort polygons back to front (typically using hardware-assisted linked list bucket sorting) and dropped afterwards [1].

[1] https://github.com/spicyjpeg/ps1-bare-metal/blob/main/src/08...

Integers. You could almost emulate a PSX in a potato (Pentium MMX) with -ffast-math -O3 except for Alpha channel (transparencies) in textures.

No.

The reason is that the PlayStation doesn't have perspective-correct texcoord interpolation.

That's a separate issue from the wobbling.

Well, that’s half of it, and the other half of it is no sub-pixel coordinates.

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