wgpu's default DX12 compiler (Auto) loads whichever dxcompiler.dll the DLL
search path finds first. LightCraft ships none, so it picked up another
program's copy; one without dxil.dll beside it (e.g. DXC 1.7) warns that
the DXIL is unsigned, wgpu treats that as a compile error, its
indirect-validation pipelines fail, the device is lost and the window
never opens ("Parent device is lost", exit code 1).
Every wgpu instance (window and both compute devices) now uses
lightcraft_gpu::backend::backend_options(): wgpu's env options with the
DX12 compiler pinned to FXC (d3dcompiler_47.dll, part of Windows), unless
WGPU_DX12_COMPILER asks for another.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
`--help`, the module doc and the README promise that a `--memory` session
"writes nothing", and the desktop app broke that in two places:
- `PrefsWriter` saved `ui.json` whenever the UI state changed (issue #164),
so a throwaway session's `thumbSize`, window layout or language replaced
the user's saved settings — the README showcase script does exactly that.
- The GPU crash sentinel from #136 armed itself in every session except
`LIGHTCRAFT_NO_PREFS` (issue #169); `with_init_marker` creates the
settings folder to hold `gpu-init.marker`, removes the marker and leaves
the folder, so a `--memory` run on a fresh home left an empty
`Library/Application Support/LightCraft` behind.
Now `PrefsWriter` carries its target path (`None` for `--memory`,
`LIGHTCRAFT_NO_PREFS` or no home folder) and writes nothing without one; it
also writes nothing while the session is the one offered when the library
can't be opened (the question window and Continue Without Saving, which
`docs/control-protocol.md` already describes as writing nothing) and
resumes when `app.openLibrary` ends it. `gpu_crash_check(in_memory)` neither
arms the sentinel nor removes a marker in a `--memory` session; it still
reads one (new `read_init_marker`), so GPU rendering starts off there too
and the next ordinary launch reports and clears it. A `--memory` session
still reads `ui.json`, but a damaged one is reported and left in place
rather than set aside. Normal launches are unchanged.
Tests: `prefs_writer_writes_nothing_in_a_memory_or_temporary_session`,
`memory_session_leaves_the_gpu_marker_and_folder_alone`,
`memory_session_leaves_a_damaged_ui_json_alone` (apps/lightcraft), and
`read_init_marker` coverage in the gpu crate's marker test.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
wgpu loads the driver of every backend in an instance's set while it
enumerates adapters. The compute device (crates/gpu) hard-coded
Backends::PRIMARY (Vulkan + DX12 + Metal) and ignored WGPU_BACKEND, and
was created from LightcraftApp::new on a background thread at launch, so
a crashing Vulkan driver (Intel UHD 630, igvk64.dll) killed the process
before the window appeared; the window (egui-wgpu) also listed Vulkan.
- lightcraft_gpu::backend: DX12 only on Windows (Metal on macOS, as before
on Linux) for both the compute device and the window;
LIGHTCRAFT_GPU_BACKEND=dx12|vulkan|metal|gl|auto|off, else WGPU_BACKEND;
backends missing from the build fall back to the default.
- The device is created only when GPU rendering is enabled, after the
first frame; the preference is applied before the window opens.
- Crash sentinel: gpu-init.marker in the settings folder around device
creation; if left behind, the next launch starts with GPU rendering off
and a notice saying how to turn it back on.
- Tests: backend parsing/selection, sentinel, window defaults, headless
snapshot with LIGHTCRAFT_GPU=0 / LIGHTCRAFT_GPU_BACKEND=off.
- Docs: gpu-pipeline.md (backends, env vars, troubleshooting), whats-new,
parity LR-BEHAV-GPU.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
