[Copak731]

What and why

ubd_on() (inline uniform updates inside an open pass deferred to the pass end, the draws after them reading a shadow) was off whenever tbdr_on() was, "because TBDR mode reorders passes". So with DM_NVN_TBDR=1 every inline update inside a pass ended it again, bringing back the passes and attachment traffic the deferral had removed (BotW about 158 → 386 passes), and the TBDR mode's own gain could not be measured on its own.

TBDR mode's reorderers never move a draw across an update: defer_try refuses an OP_UPDATE_UB between the deferred pass and its target pass or in the target pass before its first draw, fuse_try stops at one, the multi-draw scan (mdx_run) stops at one that writes a record it copied, hoist_try moves only clear-only passes (they read no uniforms), and the layer lookahead already asks ubd_on. A deferred pass replayed later reads the updates made before it, whether still deferred (shadows) or landed. ubd_on therefore no longer depends on tbdr_on; DM_NVN_UB_DEFER=0 still turns the deferral off. Nothing changes by default (TBDR mode is off). A step toward #159, alongside #1340 (store lookahead and bindless readers); the two are independent.

Reference entry: docs/reference/rendering.md, "Deferred uniform updates in TBDR mode".

Checked

• Tests: new make -C dm/gfx/tests GAME=01007EF00011E000 check_t_tbdr_ubd (production mtl_exec with DM_NVN_TBDR=1, a fragment shader returning a uniform buffer's first float4, closed-form pixels): an update between two draws of one pass, one before a same-target continuation, one before a pass defer_try defers into a later one, and one between that pass and its target pass (must not be deferred). On main the pixels pass and the 6 counter checks fail (the updates end the passes); with the change 21/21. Negative control: with OP_UPDATE_UB taken out of defer_try's refusals, the last case draws the later update's colour (64 pixels wrong). make -C dm/gfx/tests GAME=01007EF00011E000 run: every other target as on main (t_border, t_transform_feedback, t_pso_archive fail in a checkout whose path has a space, dm/gfx/tests: three targets fail when the checkout path contains a space #1341; t_nvn aborts on both).
• Games run: none. The default replay is unchanged (tbdr_on() still off), so scripts/regress.py was not run.
• Devices and OS: MacBook, Apple M5, macOS 26.6.2, Xcode 27.2.

Docs

• The finding is in its docs/reference/rendering.md entry (and docs/env_switches.tsv), and python3 dm/tools/docs_symptoms.py was run (the symptom index)
• No game files, keys or data extracted from a game in the change or the attachments

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