feat(qt): renderer tier, GPU selection and a real shader build

Joren/qbz

0 Fork 0

Closes PARITY-DEBT #83 and #104, and unblocks the immersive shader scenes.

THE TIER. Slint resolves one bool, use_gpu_renderer, and hands it to three
features: the shader scenes, the dynamic background and half of reduce-motion.
This port had none of it, which is why the scenes could not be offered — off
the GPU tier they render black and nothing could tell. QbzShell now carries
rendererApi, gpuTier, shaderScenesAvailable and appBackgroundAvailable, all
written from one latch. Only QML can source it: QRhi picks the backend after
QGuiApplication, so the pre-init code knows only what it asked for.

Per-item GraphicsInfo.api stays where it is. "Can this item draw?" and "should
this feature be offered?" are different questions, and routing the first
through Rust would make every cover wait on a round trip.

SHADERS ARE BUILT NOW. build.rs bakes every .frag/.vert to .qsb with ten
variants and the batching rewrite. They used to be baked by hand and committed
carrying no GLES variants at all, so any GLES context failed them with "No
GLSL shader code found" — which is exactly how the NPB Large visualiser went
blank while this branch was being tested. Adding a scene is now dropping a
.frag in the folder.

GPU SELECTION enumerates real devices through Vulkan and lists them by model,
never by class: a machine with no discrete GPU can no longer be told to use
one. Legacy class keys still resolve, but only against hardware that exists.
Picking a non-default device implies the Vulkan backend, which the row's own
description states in all eight locales — measured as the only route that
keeps a working context: DRI_PRIME lands on llvmpipe and the NVIDIA PRIME
pair lands on OpenGL ES.

The renderer row gains the auto-revert sentinel and the frame-liveness
watchdog it shipped without. The sentinel arms only for a choice that truly
forces a backend, and liveness means frames rendered over a window, not merely
a window that opened.

Also fixes the kiosk toggle overwriting the tier half of reduce-motion.

Verified by 312 tests, both QML audits, the offscreen smoke, and a probe
against the real hybrid GPU: both devices enumerate by name and the stored
preference applies.

cc

This commit is contained in: