Hand Android's develop frame to the compositor as a texture again
With Skia drawing pre-rotated on wgpu's Vulkan swapchain, Android no longer needs to draw with Skia over OpenGL, which was the only reason the develop view read its frame back through memory (TD-1). So `unstable-wgpu-29` moves back to the common slint dependency. The android-activity backend then builds `SkiaRenderer::default_wgpu_29`, and `shared_gpu` loses its Android arm. The one wgpu device is handed to Slint through `BackendSelector::require_wgpu_29` on both platforms. `slint::android::init_with_event_listener` runs before `dr_ui::run`, so the selector reaches the Android adapter before its window exists. `renderer-femtovg-wgpu` stays desktop-only, since Android has no FemtoVG. The two `#[cfg(target_os = "android")]` readbacks in `develop::render` (the frame through `export_pixels` and the focus overlay through `read_overlay`) are gone. `read_overlay` stays for the tests that check what the overlay marks. Built for arm64 and release-signed. Not yet run on the tablet.
This commit is contained in:
@@ -470,7 +470,7 @@ impl FocusPeakPass {
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// TEXTURE_BINDING to be sampled by the compositor.
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// RENDER_ATTACHMENT is not used by anything here and is required
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// anyway: Slint rejects an imported texture without it. COPY_SRC
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// is for `read_overlay` and its two callers.
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// is for `read_overlay` and the tests that call it.
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usage: wgpu::TextureUsages::STORAGE_BINDING
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| wgpu::TextureUsages::TEXTURE_BINDING
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| wgpu::TextureUsages::RENDER_ATTACHMENT
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@@ -490,18 +490,11 @@ impl FocusPeakPass {
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/// TRACES: AC-8
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/// Copy the overlay to the CPU, as RGBA8 rows with no padding.
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///
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/// **Two callers, and neither is the desktop display path.** The tests
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/// below are one: an overlay is a claim about which pixels are sharp, and
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/// there is no way to check that claim without looking at the pixels. The
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/// other is the Android develop view, which reads the *frame* back for the
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/// reasons `technical-debt.md` TD-1 records — wgpu's Android swapchain
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/// tears a portrait window, so Slint is not drawing with wgpu there and no
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/// texture can be handed over. An overlay that stayed on the device on a
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/// platform where the picture underneath it does not would simply never be
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/// seen.
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///
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/// On desktop nothing calls this, and ARCH §6.1 holds on the path that
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/// matters: the overlay reaches the compositor as a texture.
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/// **The tests below are the only caller, and never the display path.** An
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/// overlay is a claim about which pixels are sharp, and there is no way to
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/// check that claim without looking at the pixels. On screen, on desktop
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/// and Android alike, the overlay reaches the compositor as a texture and
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/// ARCH §6.1 holds. (Android read it back here until TD-1 was paid off.)
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pub fn read_overlay(&self) -> Result<(Vec<u8>, u32, u32), GpuError> {
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let Some(layer) = self.layers[self.current].as_ref() else {
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return Err(GpuError::Readback("no overlay has been rendered".into()));
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@@ -6,7 +6,7 @@
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//! module doc said for eight releases that it held no pipeline and no masks.
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//! It holds both now, plus demosaic, detail, segmentation masks, two
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//! histograms and focus peaking. The zero-copy claim is still the one that
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//! matters, and TD-1 records the one platform where it does not hold.
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//! matters, and since TD-1 was paid off it holds on Android too.
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//!
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//! Deliberately free of UI dependencies (ARCH §6.5a). The texture is handed
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//! out as a `wgpu::Texture`; who composites it is not this crate's concern.
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+37
-37
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+11
-13
@@ -87,14 +87,16 @@ rusqlite.workspace = true
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# Consequence worth stating plainly: the desktop app now needs a working wgpu
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# adapter to open a window at all. Slint refuses a CPU adapter for this
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# renderer unless `SLINT_WGPU_CPU` is set in the environment.
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# TEST BUILD: the wgpu renderer features have moved to the desktop-only
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# dependency below. On Android they made `AndroidWindowAdapter` choose
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# `SkiaRenderer::default_wgpu_29`, and so put the app on wgpu's Vulkan
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# swapchain — which hardcodes `preTransform = IDENTITY` (gfx-rs/wgpu#3345).
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# Without them the Android backend uses `SkiaRenderer::default`, which on
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# Android resolves to Skia over OpenGL, where the driver owns the display
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# rotation and there is no transform to get wrong.
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slint = { workspace = true, features = ["compat-1-2"] }
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#
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# On Android the renderer is Skia, not FemtoVG — the android-activity backend
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# has no other — so `renderer-femtovg-wgpu` stays with winit below, and only
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# `unstable-wgpu-29` is shared. With it, `AndroidWindowAdapter` builds
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# `SkiaRenderer::default_wgpu_29`: Skia drawing on wgpu's Vulkan swapchain,
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# which is what lets it sample our texture. That swapchain used to tear in
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# portrait on a landscape-mounted panel (gfx-rs/wgpu#3345), and Android drew
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# with Skia over OpenGL behind a readback instead; the patched wgpu-hal and
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# Skia renderer in third_party/ pre-rotate it, which closed TD-1.
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slint = { workspace = true, features = ["compat-1-2", "unstable-wgpu-29"] }
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wgpu.workspace = true
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anyhow.workspace = true
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# `SettingsError` distinguishes an io failure from a malformed file, which the
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@@ -110,11 +112,7 @@ serde_norway = { workspace = true, optional = true }
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# under `cfg(target_os = "android")`, so this only has to name the feature;
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# cargo resolves it away entirely on desktop.
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[target.'cfg(not(target_os = "android"))'.dependencies]
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slint = { workspace = true, features = [
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"backend-winit",
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"renderer-femtovg-wgpu",
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"unstable-wgpu-29",
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] }
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slint = { workspace = true, features = ["backend-winit", "renderer-femtovg-wgpu"] }
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# The manual's `file:` URL (`manual::desktop_open`): a Windows path and a
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# path with a space in it are both URLs only after encoding, and this is the
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# crate the workspace already encodes URLs with.
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@@ -278,31 +278,10 @@ impl DevelopSession {
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// in `AdjustPass`'s texture descriptor — so a failure here is a
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// descriptor that drifted, not anything the caller did. Say that,
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// rather than surfacing "InvalidUsage" to a photographer.
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#[cfg(not(target_os = "android"))]
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{
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slint::Image::try_from(texture.clone())
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.map_err(|e| format!("the render target is not importable by the compositor: {e}"))
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}
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// Android draws with Skia over OpenGL and cannot sample a
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// `wgpu::Texture`, so the frame comes back through memory. See
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// `crate::shared_gpu`'s Android arm for why that is the trade on this
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// platform. The pass still runs on the GPU; only this last hop does not.
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#[cfg(target_os = "android")]
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{
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let _ = texture;
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let (rgba, w, h) = self
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.adjust
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.export_pixels()
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.map_err(|e| format!("reading the rendered frame back: {e}"))?;
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let mut buf = slint::SharedPixelBuffer::<slint::Rgba8Pixel>::new(w, h);
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let wanted = (w as usize) * (h as usize) * 4;
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let src = &rgba[..wanted.min(rgba.len())];
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buf.make_mut_bytes()[..src.len()].copy_from_slice(src);
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Ok(slint::Image::from_rgba8(buf))
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}
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}
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/// TRACES: FR-DSP-7
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/// Count the frame that is currently on the canvas.
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///
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@@ -463,8 +442,6 @@ impl DevelopSession {
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.ok()?
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.clone();
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#[cfg(not(target_os = "android"))]
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{
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// A layer over the canvas rather than a tint in it, so nothing
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// here reaches the histogram or an export — see `FocusPeakPass`
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// for the whole of that argument.
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@@ -473,25 +450,6 @@ impl DevelopSession {
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.ok()
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}
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// Android draws with Skia over OpenGL and cannot sample a
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// `wgpu::Texture`, so the overlay follows the frame it belongs to back
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// through memory (technical-debt.md TD-1). The measurement still
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// happens on the GPU; only this last hop does not.
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#[cfg(target_os = "android")]
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{
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let _ = overlay;
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let (rgba, w, h) = pass
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.read_overlay()
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.inspect_err(|e| log::warn!("reading the focus overlay back: {e}"))
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.ok()?;
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let mut buf = slint::SharedPixelBuffer::<slint::Rgba8Pixel>::new(w, h);
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let wanted = (w as usize) * (h as usize) * 4;
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let src = &rgba[..wanted.min(rgba.len())];
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buf.make_mut_bytes()[..src.len()].copy_from_slice(src);
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Some(slint::Image::from_rgba8(buf))
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}
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}
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/// Render the *whole* frame for the crop overlay to be drawn over.
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///
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/// Crop mode cannot use [`Self::render`]: that applies the crop, so the
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+9
-45
@@ -1071,7 +1071,13 @@ enum PointsUpdate {
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///
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/// `None` means develop is unavailable and the viewer falls back to embedded
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/// previews — the same degradation as a machine with no adapter at all.
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#[cfg(not(target_os = "android"))]
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///
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/// **The same on Android**, where Slint draws with Skia rather than FemtoVG
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/// but on this device all the same. It used to open a device of its own
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/// there and read every frame back (TD-1), because wgpu's Vulkan swapchain
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/// could not pre-rotate and a portrait window tore on the tablet's
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/// landscape-mounted panel. The patched wgpu-hal and Skia renderer in
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/// `third_party/` pre-rotate it now; see technical-debt.md TD-1.
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fn shared_gpu() -> Option<dr_gpu::GpuContext> {
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let shared = match pollster::block_on(dr_gpu::GpuContext::new_shared()) {
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Ok(shared) => shared,
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@@ -1112,45 +1118,6 @@ fn shared_gpu() -> Option<dr_gpu::GpuContext> {
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Some(ctx)
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}
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/// TRACES: FR-DSP-1 | AC-8
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/// Open the compute device on Android — and do **not** give it to Slint.
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///
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/// # Why this platform is different
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///
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/// The desktop version above exists so one `wgpu::Texture` can be written by
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/// the adjust pass and sampled by the compositor without a round-trip. That
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/// requires Slint to be drawing with wgpu, and on Android drawing with wgpu
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/// means drawing on wgpu's Vulkan swapchain — which hardcodes
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/// `preTransform = IDENTITY` (gfx-rs/wgpu#3345).
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///
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/// On a tablet whose panel is mounted landscape, portrait then presents an
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/// unrotated buffer, every present returns `VK_SUBOPTIMAL_KHR`, and the frames
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/// arrive torn. Measured on the device: portrait sits on `composition=CLIENT`
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/// with `bufferTransform=ROT_270`, landscape on `composition=DEVICE` with
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/// `ROT_180`, and only portrait tore. Taking Slint off wgpu — it then uses
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/// Skia over OpenGL, where the driver owns the rotation — fixed it.
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///
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/// # What it costs, and why that is the right trade here
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///
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/// Without a shared device the display path needs a readback:
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/// `AdjustPass::export_pixels` instead of `Image::try_from(texture)`. That is
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/// the transfer ARCH §6.1 and AC-8 exist to avoid, and it is still the better
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/// bargain on this platform — the alternative is not a faster develop view, it
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/// is a torn one, in the orientation a tablet is mostly held in.
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///
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/// The compute passes are untouched: demosaic and adjust still run on the GPU,
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/// on this device. Only the last hop to the screen goes through memory.
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#[cfg(target_os = "android")]
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fn shared_gpu() -> Option<dr_gpu::GpuContext> {
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match pollster::block_on(dr_gpu::GpuContext::new_headless()) {
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Ok(ctx) => Some(ctx),
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Err(e) => {
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log::warn!("no GPU for the develop passes: {e}");
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None
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}
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}
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}
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/// TRACES: M-13 | M-14
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/// Build and run the viewer.
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pub fn run(paths: Vec<PathBuf>) -> Result<()> {
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@@ -1181,11 +1148,8 @@ pub fn run(paths: Vec<PathBuf>) -> Result<()> {
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// app still browses through the preview path, just without develop.
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//
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// Timed rather than moved: this is a Vulkan instance, an adapter
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// enumeration and a device request, none of which can be deferred on the
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// desktop because the backend must be chosen before a window exists. On
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// Android it could be — nothing shares that device with the compositor
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// (TD-1) — but "could be" is not "costs enough to be worth it", and this
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// line is what will say which.
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// enumeration and a device request, none of which can be deferred
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// because the backend must be chosen before a window exists.
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let gpu = shared_gpu();
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log::info!("gpu opened in {} ms", launch_began.elapsed().as_millis());
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