Ah, this is a classic "RGB overlay", as pioneered by Matrox for the workstation market, which doesn't really mean much, and I assume is fully emulated on a mode

Ah, this is a classic "RGB overlay", as pioneered by Matrox for the workstation market, which doesn't really mean much, and I assume is fully emulated on a modern chip. Nothing like a modern overlay pipe like you see in the CRTCs on mobile chips.