The GameCube is not, generally, resolution-agnostic. The internal framebuffer is 640x528 pixels wide, and the hardware has this hardwired in certain places, lik

The GameCube is not, generally, resolution-agnostic. The internal framebuffer is 640x528 pixels wide, and the hardware has this hardwired in certain places, like the VI/scanout subsystem. Games themselves even allocate the scanout buffers (XFBs) with a constant size, but they usually just submit a command to copy from the GPU's internal framebuffer (the EFB), so Dolphin can just track the memory address they send in the command and swap that out with a larger framebuffer it allocated itself. This is what I mean by "virtual XFB".