4 ms·

> 320 * 200 pixels @ 30 fps means they needed to calculate 1,920,000 pixels per second. With a 33 Mhz CPU, that's ~17 clock cycles per pixel, and that doesn't a

> 320 * 200 pixels @ 30 fps means they needed to calculate 1,920,000 pixels per second. With a 33 Mhz CPU, that's ~17 clock cycles per pixel, and that doesn't account for time to handle game logic. GPUs, even the primitive PSX one, will draw many in a single CPU cycle. I can't find information on the PSX GPU fill rate but I'm sure it's faster than 1 pixel per CPU cycle. DOOM didn't use the GPU to draw the walls/floors as triangles but did use the GPU to draw the scene as vertical strips. DOOM also relied on the 1Kbyte "scratchpad RAM" which was the CPU cache mapped into the address space and not subject to DMA delays.

xgkickt 5y ago
>GPUs, even the primitive PSX one, will draw many in a single CPU cycle. I can't find information on the PSX GPU fill rate but I'm sure it's faster than 1 pixel per CPU cycle. Two pixels per cycle for flat shaded or rectangular primitives. Add another cycle for color interpolation, and another for on-cache texture reads (divided by how many texels are packed into 16 bits). The GPU is clocked around 53MHz so the range of 'many' here is roughly 1 to 4, ignorning that a CPU renderer would probably write two pixels at once. The CPU is also hampered by main memory reads taking a minimum of 5 cycles. Pipelining helps a little but extensive scratchpad use, such as putting the stack on it, was essential. DOOM PSX did use triangles for the walls, just that they were a single pixel wide.
Sohcahtoa82 5y ago
> GPUs, even the primitive PSX one, will draw many in a single CPU cycle. I can't find information on the PSX GPU fill rate but I'm sure it's faster than 1 pixel per CPU cycle. GPUs do it via massive parallelization. > DOOM didn't use the GPU to draw the walls/floors as triangles but did use the GPU to draw the scene as vertical strips. DOOM also relied on the 1Kbyte "scratchpad RAM" which was the CPU cache mapped into the address space and not subject to DMA delays. In the days of DOOM, did the video card even offer any sort of acceleration? I was under the impression that all the texture scaling was done on the CPU. So while it rendered walls as vertical strips, it would still have to interpolate across the strip on the CPU.
- Narishma 5y ago
  There's a misunderstanding about which version of Doom people are talking about. I think you're talking about the PC version while the person you replied to was talking about the PS1 version.
Narishma 5y ago
I may be misunderstanding but I think they were talking about the PC version of Doom.

xgkickt 5y ago

>GPUs, even the primitive PSX one, will draw many in a single CPU cycle. I can't find information on the PSX GPU fill rate but I'm sure it's faster than 1 pixel per CPU cycle. Two pixels per cycle for flat shaded or rectangular primitives. Add another cycle for color interpolation, and another for on-cache texture reads (divided by how many texels are packed into 16 bits). The GPU is clocked around 53MHz so the range of 'many' here is roughly 1 to 4, ignorning that a CPU renderer would probably write two pixels at once. The CPU is also hampered by main memory reads taking a minimum of 5 cycles. Pipelining helps a little but extensive scratchpad use, such as putting the stack on it, was essential. DOOM PSX did use triangles for the walls, just that they were a single pixel wide.

Sohcahtoa82 5y ago

> GPUs, even the primitive PSX one, will draw many in a single CPU cycle. I can't find information on the PSX GPU fill rate but I'm sure it's faster than 1 pixel per CPU cycle. GPUs do it via massive parallelization. > DOOM didn't use the GPU to draw the walls/floors as triangles but did use the GPU to draw the scene as vertical strips. DOOM also relied on the 1Kbyte "scratchpad RAM" which was the CPU cache mapped into the address space and not subject to DMA delays. In the days of DOOM, did the video card even offer any sort of acceleration? I was under the impression that all the texture scaling was done on the CPU. So while it rendered walls as vertical strips, it would still have to interpolate across the strip on the CPU.

Narishma 5y ago
There's a misunderstanding about which version of Doom people are talking about. I think you're talking about the PC version while the person you replied to was talking about the PS1 version.

Narishma 5y ago

I may be misunderstanding but I think they were talking about the PC version of Doom.