D780 - Window space before the divide is drawn under the window-space viewport

Status: decided Date: 2026-10-09 known_by: published (gfx103.json PA_CL_VTE_CNTL: the six scale and offset enables, and VTX_XY_FMT / VTX_Z_FMT saying whether x, y and z arrive already divided by W)

A draw whose PA_CL_VTE_CNTL has every field orbistoun reads at zero has its positions in window space before the divide. There is no viewport scale or offset, and the hardware divides x, y and z by the fourth component, so the pixel is (X / W, Y / W) and the depth Z / W. Its primitive shader writes (X / S, Y / S, Z, W), and the draw takes the fixed window-space viewport D731 uses, scale S = WINDOW_SPACE_SCALE and offset zero. Vulkan's divide and scale then give back the same pixel and depth. D731's form, radeonsi's pre-divided one with 1/W in the fourth component, is unchanged.

Why: PPSA02664's fullscreen passes write PA_CL_VTE_CNTL zero, and every such draw was refused as a viewport transform turned off.