PowerVR-Series1

It is a shame that SciTech Display Doctor / UniVBE was never opene sourced. It probably contains a lot of wisdom and info to get all those special modes and probably would of been helpful for quirks and such that documentation lacks and only a concrete implementation would of found. On a side note, the PowerVR-Series1[0] released their source code for their GPU but stated that > As of right now, due to licensing concerns we have been unable to supply some libraries and headers provided by SciTech Software for "The Universal VESA VBE" I wonder if there has been efforts by this community, such if anybody has a connection to SciTech / Kendall Bennett / or finding out if IBM had source code releasing rights for that part of the operating system when they made it the native driver to OS/2. [0] https://github.com/powervr-graphics/PowerVR-Seri

Imagination released the driver and simulator sources for PowerVR series 1 last year [0] which is a fun resource to see how tiling GPUs started. Series 1 is particularly weird because it doesn't use triangles, it uses infinite planes, which may be clipped by other planes - meaning that convex polygons with more sides are faster than the equivalent in triangles. Sadly no RTL but I'm guessing the simulator is based on it given some of the weird coding patterns. [0] - https://github.com/powervr-graphics/PowerVR-Series1

I had some fun digging through the PowerVR Series 1 source code [0] that was released earlier in the year. It includes a simulator that you can use to piece together how the hardware itself worked, some of it certainly looks like a rough translation from the RTL... [0] - https://github.com/powervr-graphics/PowerVR-Series1

PowerVR was especially funky. They used planes to ‘carve’ out polygons. It meant that they could genuinely draw convex polygons with arbitrary numbers of side by using ~N+1 planes. I found it kind of cool to try and read through the simulator code in their open source release [0]. I imagine there would be an interesting write up if someone sat down and really wanted to understand it. [0] - https://github.com/powervr-graphics/PowerVR-Series1

The code [1] includes an implementation of the FastInvSqrt that date back at least to 1996. There's an assembly and a C version, referred as SLOW_SQRT_DIV :). It uses float/int pruning through union (in C) and one or two rounds of Newton-Raphson refinements. Interestingly corrections aren't done with a fixed value (part of the famous 0x5F3759DF) but through a LUT [2], which I guess, yield better results but was a bit slower on 90's arch. [1] https://github.com/powervr-graphics/PowerVR-Series1/blob/mai... [2] https://github.com/powervr-graphics/PowerVR-Series1/blob/mai...

Code is problematic: multilne defines: https://github.com/powervr-graphics/PowerVR-Series1/blob/c8c... Looks like they didn't know the "do{...}while(0)" trick.