GPU calculated physics works just fine when results are brought back to the Cpu.
Raycasting for game logic is cpu based as you mention because the game logic itself is on the cpu. Yet solvers and the true heavy lifting does work well on gpu.
Except, and this is the true reason we see little gpu physics, no one has spare gpu room. Thus cpu side physics wins for most games. Outside specific physics focused games giving up graphics for faster physics is not a profitable trade.
I say this as a gamedev myself who has several times made this exact decision.
The biggest problem with GPU physics is that it's a very difficult problem to tackle and you'll run into compatibility issues between the hardware vendors. It'll work on Nvidia hardware and won't work on AMD or vice versa.
Many games do have spare GPU room to spare, but since there are no good GPU-accelerated solutions for physics they don't have much of a choice.
> The biggest problem with GPU physics is that it's a very difficult problem to tackle
This is a completely meaningless statement.
> you'll run into compatibility issues between the hardware vendors
Those compatibility issues already exist in the form of DX or OpenGL drivers, and most games have to face them. Writing a sim in OpenCL would work on both Nvidia and AMD, and even on Integrated GPUs.
> Many games do have spare GPU room to spare
Many smaller games mighy but most big games do not. And those games with GPU room to spare normally have CPU to spare.
>since there are no good GPU-accelerated solutions for physics
How is "difficult to implement" a meaningless statement?
>Those compatibility issues already exist in the form of DX or OpenGL drivers, and most games have to face them. Writing a sim in OpenCL would work on both Nvidia and AMD, and even on Integrated GPUs.
With completely different performance characteristics and very difficult to diagnose bugs.
>Many smaller games mighy but most big games do not. And those games with GPU room to spare normally have CPU to spare.
Maybe if you're talking about mainstream AAA single player titles, but many multiplayer titles tend to have CPU limits instead.
>There is - PhysX.
Which only works on nvidia hardware and is thus a useless solution.
Raycasting for game logic is cpu based as you mention because the game logic itself is on the cpu. Yet solvers and the true heavy lifting does work well on gpu.
Except, and this is the true reason we see little gpu physics, no one has spare gpu room. Thus cpu side physics wins for most games. Outside specific physics focused games giving up graphics for faster physics is not a profitable trade.
I say this as a gamedev myself who has several times made this exact decision.