dtourolleandClaude Opus 5
cf8f5b632f
The oldest open item in the project (ARCH §6.1, spike S1, AC-8). Every frame
in develop was read off the GPU into a `SharedPixelBuffer` and handed back to
Slint to upload again: ~7 ms at 4K against a 0.28 ms compute pass, 96% of the
frame spent carrying pixels to the CPU and back so they could be drawn where
they already were.
Slint 1.17 will adopt a `wgpu::Texture` directly, and the whole of what that
needs is arrangement rather than code.
**One device, made before the window.** A texture belongs to the device that
allocated it, so the compute passes and the compositor cannot each open their
own. `GpuContext::new_shared` opens one and hands back the instance and
adapter alongside it; `dr_ui::shared_gpu` gives all four to
`BackendSelector::require_wgpu_29(WGPUConfiguration::Manual { .. })`. That
call has to come before the first window, because creating one selects a
backend for you — which is why the GPU is now opened at the top of `run`
rather than two hundred lines down beside the other controllers.
dr-gpu still names no UI type. It hands out raw wgpu and does not ask who is
compositing (ARCH §6.5a).
**Vulkan only on the shared path**, where headless keeps its GL fallback.
wgpu's GL backend reaches its display through EGL at instance creation, and
before a window exists there is no display handle to give it — so a GL
instance cannot later produce the window surface Slint needs from it. A
machine with no Vulkan gets no shared device and browses without develop,
which is the same degradation as no adapter at all.
**`renderer-femtovg` becomes `renderer-femtovg-wgpu`.** The old one is FemtoVG
over OpenGL and cannot be handed a wgpu texture at all. It is not kept
alongside as a fallback: FemtoVG-over-GL has no branch for an imported
texture, falls through to "render this image into a buffer", gets nothing, and
draws nothing — a blank canvas with no error, which is worse than the failure
it would be papering over. The consequence is stated plainly in the manifest:
the desktop app now needs a working wgpu adapter to open a window.
**Two output textures, not one, and this is the part that is not obvious.**
Slint repaints when the image property *changes*, and it decides that with
`PartialEq` — which for two images over the same `wgpu::Texture` says
"unchanged". A pass that reused a single target would have rendered every
slider move correctly on the GPU and shown none of them: right, and invisible.
`AdjustPass` alternates between two targets, so consecutive frames are
genuinely different values. It also settles the read-while-write question that
one queue was already answering.
`RENDER_ATTACHMENT` is added to both render targets. Neither pass uses it;
Slint rejects an imported texture without it, on the reasoning that a
compositor handed a texture may need to draw into it.
**`AdjustPass::read_output` is deleted rather than gated.** It and
`export_pixels` were the same transfer under two names, and the comments
explaining why they were separate are the point of the whole criterion:
reading pixels back to *display* them is the defect, reading them back to
*encode a file* is the only way a file is made. The display twin is now gone
outright, which is stronger than a feature flag — it cannot be turned back on.
`export_pixels` is untouched and still ungated. The `readback` feature comes
off dr-ui, darkroom-desktop and darkroom-android; it stays in dr-gpu, where it
still gates `RenderTarget::read_pixels` and the segmentation field readback.
`examples/develop` moves to `export_pixels`, which is honest — it writes a
PPM — and so no longer needs the feature.
Four tests, each named for what it protects and each of which fails without a
screen if the property it guards breaks:
- the adjust target satisfies every condition Slint's import checks, asserted
in the crate that owns the descriptor, because a descriptor that drifts
fails at runtime on a real display and nothing else would notice;
- consecutive renders are different textures, and the third is the first
again, so the alternation is a rotation and not an allocation per frame;
- the develop canvas has no CPU pixel buffer and does have a wgpu texture —
AC-8 itself, in the terms Slint uses;
- consecutive frames compare unequal as `slint::Image`, which is the property
the repaint actually depends on.
The zoom test's readback moves into the test module. It has to: there is no
library function that copies a displayed frame to the CPU any more, and that
is the point — the round-trip now exists in the test binary and nowhere a
shipping build can reach.
**What is not proven.** No GUI was run. What is verified is that the texture
satisfies the import contract, that the import succeeds, that the canvas is a
texture rather than a buffer, and that consecutive frames are distinguishable.
What is unverified is everything that needs a display: that Slint's FemtoVG
wgpu renderer adopts the Manual configuration on a real surface, that the
picture appears the right way up and the right colour, and the frame timing
that motivated the whole exercise. Android is untouched by testing — the
android backend routes a WGPU29 request to Skia, whose wgpu surface does
handle imported textures, but that is read from the source, not observed.
56 dr-gpu tests and 255 dr-ui tests pass, clippy clean under `-D warnings`,
fmt clean.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
35 lines
1.3 KiB
TOML
35 lines
1.3 KiB
TOML
[package]
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name = "darkroom-android"
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version.workspace = true
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edition.workspace = true
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rust-version.workspace = true
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license.workspace = true
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# A cdylib, not a bin: Android loads the app as a shared library and calls
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# `android_main` through android-activity's glue. Nothing execs a binary, so
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# there is no `main` to provide.
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[lib]
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name = "darkroom"
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crate-type = ["cdylib"]
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[dependencies]
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# No backend feature to select: dr-ui picks its Slint backend from the target,
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# so building for aarch64-linux-android gets android-activity automatically.
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dr-ui.workspace = true
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# For `session::set_data_dir`: only the platform entry point knows where Android
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# lets this app keep files, and it must be set before any store is opened.
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dr-sync-nextcloud.workspace = true
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# Directly, not just through dr-ui: `android_main` takes an `AndroidApp` and
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# calls `slint::android::init`, both of which come from this crate. The backend
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# feature comes from dr-ui's target-specific dependency.
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slint.workspace = true
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log.workspace = true
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android_logger = "0.15"
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[features]
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# Mirrors darkroom-desktop: the CPU readback path is gone since S1 landed
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# zero-copy. It mattered more here than on desktop — the same wrong path with
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# far less memory bandwidth to absorb it (ARCH §6.1) — but it is untested on a
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# device, since S1 was verified on desktop only.
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default = []
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