D904 - A dispatch samples through its guest sampler

Status: decided Date: 2026-10-19

A compute program's image sample reads through the sampler its program names, the same as a draw's (D690): filter, address modes and border are decoded from the sampler words, and a Vulkan sampler is cached per device and sampling. A fetch ignores the sampler.

A compute stage has no derivatives. A sample there is translated only at a named level (_lz, _l) or with explicit gradients (_d). A sample whose level would come from derivatives is refused by name. A table border colour is refused as it is for draws.

Why: Grand Theft Auto V's compute programs sample their inputs with image_sample_lz. With no sampler bound the dispatch could not be built.

Rejected:

• One nearest sampler for every dispatch: it drops the linear filtering the programs ask for.
• Treating an implicit-level sample in compute as level 0 silently: the hardware takes its derivatives from the quad, and the guess is not written down anywhere.