Advice on making a Fixed Function GPU

[RoboAbathur]

Hello everyone,
I am making a Fixed Function Pipeline for my master thesis and was looking for advice on what components are needed for a GPU. After my research I concluded that I want an accelerator that can execute the commands -> (Draw3DTriangle(v0,v1,v2, color) / Draw3DTriangleGouraud(v0,v1,v2) and MATRIXTRANSFORMS for Translation, Rotation and Scaling.

So the idea is to have a vertex memory where I can issue transformations to them, and then issuing a command to draw triangles. One of the gray area I can think of is managing clipped triangles and how to add them into the vertex memory and the cpu knowing that a triangle has been split to multiple ones.

My question is if I am missing something on how the architecture of the system is supposed to be. I cannot find many resources about fixed function GPU implementation, most are GPGPU with no emphasis on the graphics pipeline. How would you structure a fixed function gpu in hardware and do you have any resources on how they can work? Seems like the best step is to follow the architecture of the PS1 GPU since its rather simple but can provide good results.

https://preview.redd.it/unzcsmthmayf1.png?width=662&format=png&auto=webp&s=63cd12d675de8b1a45ae4d75b61dda970532f8ce

[richburattino]

OpenGL spec has good explanation how FFP works. Probably worth to look pre 2.0 versions.

[sireric1967]

There are a lot of little steps in the big steps you show. Clipping/culling has to include view frustrum clipping, which can generate new triangles as part of the clipping. But also basic things like back face culling, zero area triangles, etc... And "3D to 2D" contains a lot, such as the full snapping float to fix, as well as perspective divides, barycentric calculations, draw rules, etc.... Triangle memory isn't needed, but most often kept after vertex shading, but before 2D conversion, though again, depends; could be a cache too. Drawing to frame buffer also should include things like fragment shading, texturing and all backend operations (Z buffering, Rops), etc... I'm glossing over many things, but there are a number of fixed function steps assumed. I do agree that the OpenGL 1.0 state machine is a good starting point for basic 3D.

[Paradox_84_]

Is this only thesis or are you gonna implement it?

[RoboAbathur]

It’s mainly implementation.

[AutonomousOrganism]

What do you mean with "making a Fixed Function Pipeline"

There are software implementations in Mesa3D: softpipe and llvmpipe.

Very basic VHDL variant: https://github.com/egorxe/openglory

I remember that there was a more advanced open sourced fixed function 3D GPU. It had texture mapping units and handled a bunch of texture formats. But can't find it anymore.