[brycekottke]

video_core: diagnostics for task/mesh skips and null TIC descriptors

• I have read and followed the Contribution Guidelines.
• I have read and followed the AI Policy.
• I have read and followed the Coding Guidelines to the best of my ability.
• I have put [HUMANMADE] in the title if the pr was human-made

Summary

While debugging a black screen at the cutscene-to-gameplay transition in
Ocarina of Time (NUP, 0400486024DEC000) on Intel Xe-LP, three places hid the
root cause silently. This PR adds diagnostics for them:

1. vk_pipeline_cache.cpp: CreateGraphicsPipeline returned nullptr for
   task/mesh pipelines on devices without VK_EXT_mesh_shader without any log
   (a silent return nullptr), so affected draws only showed up as
   "Draw skipped ... miss=creation-failed". It now logs which stage and
   pipeline hash was skipped and why.
2. vulkan_device.cpp: one line at device init reporting VK_EXT_mesh_shader
   availability (extension loaded, taskShader/meshShader feature bits, final
   enabled state), so "does this device take the mesh path" is answerable
   from a log alone. ANV only enables task/mesh on Arc-class hardware; on
   Xe-LP the extension is advertised by other vendors' stacks but silently
   absent here, which cost a full debugging session to establish.
3. Null TIC diagnostics: a format-0 TIC decodes to address 0, 1x1x1 — a
   benign placeholder the game binds to handle 0 (the lookup already falls
   back to A8B8G8R8). shader_environment.cpp logs the raw words of such
   TICs bound in shaders (handle included), and image_info.cpp logs the
   raw words of format-0 TICs entering the texture cache, deduplicated per
   descriptor. This distinguishes the placeholder from a real unmapped NX2
   format, which would otherwise look identical in the format_lookup_table
   assert.

Root cause of the black screen itself (for the record): the title's gameplay
scene passes use NVN task + mesh programs, which are skipped entirely on
devices without VK_EXT_mesh_shader; the offscreen scene targets stay empty.
Confirmed by running the same title on llvmpipe (supports task/mesh in
software): no skips, no black screen. This is a hardware support gap, not an
emulator bug — a compute lowering for task/mesh programs is the eventual
fix, and NX2_NOTES row 89 records the ISBE layout such a lowering needs.
These diagnostics exist so the next person reaches that conclusion in
minutes instead of hours.

This PR was written with AI assistance (agent-assisted debugging and patch
authoring), reviewed and tested by a human.

Type of change

• [] Bug fix
• Game compatibility / game-support
• Performance
• New feature
• Refactor / cleanup
• CI / build
• Documentation

Related issues

None found; this documents the diagnosis of the Xe-LP black screen.

Testing

• Tested on Windows
• Tested on Linux
• Tested on macOS
• Tested on NVIDIA
• Tested on AMD
• Tested on Intel

Games tested:

The Legend of Zelda: Ocarina of Time (NUP) — reaches gameplay on llvmpipe
with no mesh skips; on Intel Xe-LP the new warnings fire exactly once per
placeholder descriptor and once per skipped task/mesh pipeline.

Checklist

• I built it locally and it compiles without new warnings
• I did not add any copyrighted game data, keys or firmware
• Docs updated if needed
• I added AI Disclosure if one was used

Screenshots / logs

Before (Xe-LP, gameplay transition):

Draw skipped (no pipeline): vs=0x... ps=0x... rt0=0x... 128x128 miss=creation-failed
(repeated, no reason given; screen stays black)

After:

Skipping task shader pipeline 0x46cc6aaba42f700f: the device has no VK_EXT_mesh_shader
VK_EXT_mesh_shader: extension NOT loaded taskShader=0 meshShader=0 -> enabled=false
TIC with INVALID format bound to handle 0x0: raw={...} addr=0x0 1x1x1 type=0 hv=3
(warning, once per distinct placeholder descriptor)

[github-actions]

Retargeted to nx2-experimental for pre-build testing. It will be promoted to nx2 after validation.

[brycekottke]

Hope this helps a bit. while i was debugging a black screen in Ocarina of Time on a X1 thinkpad (i know, not much of a graphics card. Intel Xe-LP) i found a few places failing silently. this PR just adds log lines for skipped task/mesh pipelines, VK_EXT_mesh_shader availability at device init, and placeholder TIC descriptors. there's more details in the PR description. anyway. great work y'all! very cool project.