perf(agc): keep unchanged guest layers of a depth plane copy

[oneandonlydean]

What

Follow-up to #425, as asked in its review.

DepthPlaneCopy (sampling a depth surface as a 2D array, a cube or its integer bits) keeps each slice it read from guest memory in its staging buffer, together with the write generation it was read at. The next use reads and detiles that slice again only when:

• its address, size or tiling changed;
• the write tracker reports a write since (UnchangedSince);
• recorded GPU work writes the range (Recorder::SnapshotWriteOverlaps); or
• a depth surface held that slice in between.

Without write watching, every use reads, as before.

#425 is merged, so this head is rebased onto main 1c5e628 and holds only its own commit. It applied without conflicts and the change is the same.

Why

Every use read and detiled every slice no depth surface holds, even when nothing had written it.

The rule is the one a cached sampled snapshot already uses for a hit (cachedTexture: collect, then UnchangedSince), plus the pending-write check, so it is no looser than the existing texture path.

Tested

Linux (CachyOS, GCC 16.2.1, Release with CI's configure flags and ANYPS5_ENABLE_SPIRV_TOOLS=ON, full build and libs), RTX 4090, NVIDIA 610.57.04.

• ctest -R "agc|shader" (--parallel 4, ANYPS5_REQUIRE_VULKAN=1): 462/462 on this head (af716047), 461/461 on main 1c5e628. tools/check_conventions.py --base origin/main and tools/check_test_registration.py pass.

• The seven agc_driver_depth* tests under VK_LAYER_KHRONOS_validation: pass, no validation message.

• New agc_driver_depth_plane_guest_layers. A 2-layer D32 array: layer 0 is a depth surface, layer 1 is in watched guest memory. Checks:

  • the first use reads layer 1;
  • a second use without writes does not read it;
  • a CPU write and a driver store (MarkWritten) each make the next use read it again.

  It passes with the change (5 of 5 runs). On main 1c5e628 with only the test added it fails: sampling the depth planes again read the guest layer no depth surface holds although nothing wrote it.

• A 3D title we test with stops on main before its title scene without feat(libSceAgcDriver): storage image access to depth surfaces #4500, so it was measured on main 1c5e628 + feat(libSceAgcDriver): storage image access to depth surfaces #4500, with this and perf(agc): skip the depth plane copy when no slice changed #2491 together: frames per second in the title scene and in the menu after it.

  build	title fps	menu fps
  main 1c5e628 + feat(libSceAgcDriver): storage image access to depth surfaces #4500	0.8	0.65
  the same + this + perf(agc): skip the depth plane copy when no slice changed #2491	17.3	13.7

  Without the two changes the title scene runs at 0.6 to 0.9 fps from its first frame on (74 frames in 90 s); with them the run goes on into the first level. One run each; caches warm for the second row. In the second row feat(libSceAgcDriver): storage image access to depth surfaces #4500's store-back also bumps the write serial (see perf(agc): skip the depth plane copy when no slice changed #2491).

Not run on this head: the 2D title we test with (it ran on #2491's head, which contains this commit). Not tested on Windows or on AMD.

Checklist

• Based on current main (1c5e628, the merge of feat(agc): depth planes sampled as 2D arrays, cubes and integer views #425); no other open PR changes DepthPlaneCopy (feat(agc): retain and refresh sampled depth array storage #1368 samples depth arrays with its own storage, separately)
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed under Silent stubs in their library's technical debt file
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• Unblocks: none
• AI-assisted: yes (Claude Code)

[Mouhand-Kaddo]

Additional platform validation on standalone PR head 5f0e7304189174bbfc033f37138b06ed15e4e77a:

Windows: passed — Windows 11, supported WinLibs GCC 15.2.0 UCRT/POSIX/SEH r7; CMake 4.3.1 / Ninja.

Release / BUILD_TESTING=ON: built the selected test targets; 2 CTest cases, 0 failures, 0 CTest skips.

Tests: agc_driver_graphics, agc_driver_depth_plane_guest_layers.

Reproduce after building the test targets: ctest --test-dir <build> --verbose --no-tests=error --timeout 30 -R "^agc_driver_(depth_plane_guest_layers|graphics)$".

Vulkan: native AMD RX 6900 XT, driver 32.0.21045.5002.

Integration limitation: a local merge against main 948a526c2 has source conflicts; these results validate the standalone PR head, not a resolved merge.