D936 - A layered depth-only draw is drawn a pass per depth slice

Status: decided Date: 2026-10-21 known_by: published

A draw may have the hardware read each primitive's layer (PA_CL_VS_OUT_CNTL.USE_VTX_RENDER_TARGET_INDX) while no colour buffer is bound (CB_COLOR0_INFO COLOR_INVALID, D779). The layer then indexes the depth view's slices, DB_DEPTH_VIEW.SLICE_START to SLICE_MAX (gfx103.json: bits 10:0 with 12:11 above them, and 23:13 with 31:30). Where that view spans more than one slice, the draw runs once per slice. Each pass binds that slice's depth target, as a cube's faces are bound (D918), and keeps the primitives whose layer is its own, counted from zero (D859). After the last pass the submission's own targets are bound again.

D859 read a draw's slices from CB_COLOR0_VIEW alone. For a depth-only draw that view is unset, so it ran the draw once, keeping layer zero, and every primitive aimed at another slice was culled.

Why: Grand Theft Auto V draws each point light's shadow cube in one depth-only draw, and its primitive shader sends each triangle to its face. Only face 0 was drawn. The lighting pass then sampled faces 1 to 5, which nothing had drawn, and the backend refused the segment.

Rejected:

• An array depth attachment with the host's Layer output: every depth target, pipeline and depth read-back would carry a layer count only layered draws use, as D859 already found for colour.