[FifteenPen]

What and why

Nintendo Switch Sports Resort's sea (title screen, menus) drew black: its normals were right, its colour 0.

Cause. 612 of the game's 11,059 shaders, all pixel shaders, read system register 0x84 with S2UR: the fragment's size in pixels (X in bits 8..15, Y in 16..23; Mesa NAK's NAK_SV_VARIABLE_RATE), which variable rate shading makes 2 or 4. The translator did not know the register and gave 0. The sea shaders divide a blend weight by the fragment's area, so the colour came out NaN, which blend_zero (dm_az) writes as 0.

Change. SReg.VariableRate (132) reads 0x10100 in EmitSReg: the host shades every pixel, so 1 x 1. Chain change (cdef7a05ad69): translator binaries rebuilt, dmsh_chain.lock and dmsh_chain.h updated.

Reference entry: The fragment's shading-rate size reads 1 x 1.

Checked

• Tests, on this branch (main 5e1c1ae + this change), Apple silicon:
  • DMSH_TEST_XLATE=… python3 dm/gfx/tests/test_dmsh_ampere_mem.py: the new ShadingRate test passes (float(65792)); main's translator gives float(0). The file's three Pokopia tests fail with main's committed translator as well, before this change.
  • python3 -m unittest dm/tools/tests/test_docs.py, python3 dm/tools/docs_symptoms.py.
• Game run: Nintendo Switch Sports Resort (04008E001F098000, v65536), a Mac app from a provisional profile. The tree was main 04811a6 with other PRs (the game needs NVN: account for four-byte direct indexed draws using control memory #1609, SDK 21 virtual output device properties and event-only stream open (Wonder Edition movie) #1561 and the file system and hid PRs opened beside this one to boot), with this translator change: all 11,059 shaders build, and the sea on the title screen and in the menus draws blue instead of black.
• Devices and OS: Apple M4 Pro, macOS 27.2.
• Other games: the shader packages of the six other Switch 2 games on this Mac (Donkey Kong Bananza, Drag x Drive, Kirby Air Riders, Mario Kart World, Star Fox, and two builds of Ocarina of Time) have no S2R / S2UR of register 0x84, so their translation changes only in the chain version. regress.py impact: none of the profiles with usage manifests is affected; regress.py check was not run.
• Not checked: iOS.

Docs

• The finding is in its docs/reference/<subsystem>.md entry, and python3 dm/tools/docs_symptoms.py was run (the symptom index)
• A chain tool changed: dmsh_chain.py --header was run and dm/gfx/nvn/dmsh_chain.h is part of the change
• No game files, keys or data extracted from a game in the change or the attachments

[seedds]

Landed on main as b581efc with you credited as co-author, as part of the Nintendo Switch Sports Resort port (profile and note: f4b7e77). Chosen over #2373, which puts the same value in AS2r only: EmitSReg is reached by both Maxwell's S2R and Ampere's S2R / S2UR. Thank you!