Comment by dragontamer

Cloth / Hair physics in those games were graphics-only physics.

They could collide with any mesh that was inside of the GPU's memory. But those calculations cannot work on any information stored on CPU RAM. Well... not efficiently anyway.

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When the Cloth simulator in Blender runs, it generates all kinds of information the CPU needs for other steps. In effect, Blender's cloth physics serves as an input to animation frames, which is all CPU-side information.

Again: i know cloth physics executes on GPUs very well in isolation. But I'd be surprised if BLENDER's specific cloth physics would ever be efficient on a GPU. Because as it turns out, calculations kind of don't matter in the big-picture. There's a lot of other things you need to do after those calculations (animations, key frames, and other such interactions). And if all that information is stored randomly in 100GB of CPU RAM, it'd be very hard to untangle that data and get it to a GPU (and back).

In a Video Game PHYSX setting, you just display the cloth physics to the screen. In Blender, a 3d animation program, you have to do a lot more with all that information and touch many other data-structures.

PCIe is very slow compared to RAM.