He would rewrite custom rendering paths for various GPUs and common sets of extensions, allowing him to improve performance and/or improve graphics.
With Direct3D, Microsoft defines a common feature set that all GPUs supporting that version of Direct3D are required to support, and any extra functionality that GPUs might provide on top of that are locked away, completely inaccessible.
Checking the Doom 3 source code, he the main ARB and ARB2 pixel shaders paths (equivalent to dx8 shaders). Then for the older gpus that mostly support pixel shaders but not in a standards compliant way, he has an nv10 code path and a nv20 code path.
Then he has a r200 code path, which I think just improves performance on r200 graphics cards over regular ARB2.
Direct3D programmers disliking extensions make me think of the sour grapes fable.
But OpenGL providing extensions doesn't mean that Direct3D programmers are free of having to implement different code paths - if anything during the 90s with the proliferation of 3D cards and different capabilities flags, programmers had to take into account a lot of different possibilities in their rendering code (and most failed to do that with games having visual glitches everywhere).
> Direct3D is now better than OpenGL Says John Carmack
https://www.bit-tech.net/news/gaming/pc/carmack-directx-bett...
I don't like the term "poaching". It implies that the engineers who took better paying jobs did something wrong, whereas they were just trying to retain a bigger portion of the enormous value that they were creating.
My recollection was that it wasn't until NVidia started up (and broke 3dfx by poaching engineers) that OpenGL started to become 'better'. Intel was left in the dust until mobo support for DMA (?around DX5?), which allowed cards to gain quick access to RAM, which was vital for texturing (you always had to 'upload' textures to the card itself prior to that). It was the final nail in the coffin for 3fdx at that point, who still hadn't released a new card for ages, and OpenGL was finally on par with D3D. D3D had a retained mode which began to be really useful by about that time too.
At the time, many people wanted to use OpenGL because it was loads easier than Immediate Mode and a lot more intuitive to grok. I recall a certain prominant Doom developer berating D3D loudly in a private email list (John Cormack) about this very fact. Ironically, a few months later some guys released a demo for a game called "Unreal" using D3D and everyone was blown away. (circa 1995-6). More ironically, it wasn't for another year that GL Quake came to fruition.