The crate as crates.io publishes it, minus .cargo-ok, its Cargo.lock and
data/testdata (13 MB of sample files only its own tests read). Not yet
routed through [patch.crates-io]; the next commit is the patch.
The other half of the wgpu-hal patch: that one lets a caller promise a
pre-rotated swapchain, and this is the caller keeping the promise.
On configure, `WGPUSurface` reads the surface's `currentTransform`,
sizes the swapchain in the panel's orientation (swapped for a quarter
turn), tells wgpu-hal to use that transform, and before each frame
concatenates the matching rotation onto the Skia canvas. Everything
Slint draws goes through that one matrix, so an imported wgpu texture is
rotated with the rest of the window. Input is not rotated, and must not
be, because Android delivers it in window coordinates.
Three details that would each have been a visible bug:
- `resize_event` compared the new size against the swapchain's. The
swapchain is transposed while a quarter turn is in effect, so the
comparison now uses the window's size, kept beside it.
- A half turn, landscape to reverse landscape, changes the transform
without resizing the window, and wgpu-hal hides the SUBOPTIMAL that
would report it. So the transform is re-read before every frame. That
costs one query into the native window.
- The item renderer snapped the origin to the pixel grid only when the
canvas matrix was a pure translation. Under a rotation that is never
true, so portrait would have lost pixel alignment everywhere. The check
now accepts right-angle rotations and flips without scaling.
The direction of each rotation follows the Vulkan spec's reading of
preTransform (the image is drawn already rotated clockwise by the
transform). It has not been confirmed on the device yet.
wgpu-hal creates every swapchain with `preTransform = IDENTITY` (#3345).
On a tablet whose panel is mounted landscape, a portrait window then
hands Android an unrotated buffer: SurfaceFlinger falls back to rotating
it on the GPU (composition CLIENT), and on this device those frames tear.
That is why Android draws with Skia over OpenGL today, and why the
develop view pays a readback (TD-1).
The field cannot just be set to `currentTransform` inside wgpu. It is a
promise that the image is already drawn rotated and sized in the panel's
orientation, and only the renderer above wgpu can keep it. So the patch
is the smallest thing that lets that renderer ask:
`vulkan::Surface::current_transform` reads the surface's transform, and
`set_pre_transform` makes the next swapchain use it. The default stays
IDENTITY, so desktop and any caller that does not opt in behave exactly
as upstream.
The Android develop view reads its frame back through memory (TD-1)
because wgpu's Vulkan swapchain never pre-rotates, and a portrait window
on this tablet's landscape panel then tears. The fix is a small patch to
each of these two crates, and this commit is only the ground it lands on:
both are byte-for-byte the crates.io sources the lockfile already
resolved, so the commits that follow are the patch and nothing else.
third_party/ is excluded from the workspace, or every path dependency
under the root would become a member and `--workspace` would test and
lint upstream code as ours. The README says how to carry the patches
across a Slint or wgpu bump, which matters because a stale version here
does not fail the build — cargo just warns and uses the unpatched crate.
dtourolle