dr-decode exposes four entry points rather than one decode, because
callers differ sharply in what they need (ARCH §3.2): culling wants a
preview, the grid wants metadata, only develop and export touch sensor
data. Fusing them forces a full decode where a header read suffices,
which is why Lightroom stalls ~2s per image while culling.
Smoke-tested against 1,852 real Canon CR2 files (EOS 6D, ~27MB each):
metadata 0.2ms from a 256KB header read, no full decode
preview ~250ms 5472x3648, downscaled to 2048 for display
jpeg 3.0ms
Two findings worth recording:
rawler 0.7.2's CR2 decoder implements only full_image; thumbnail_image
and preview_image are unimplemented trait defaults returning None. So
every rung of the preview ladder resolves to a full-resolution decode at
~250ms — 5x over NFR-P13's 50ms budget. CR2 does carry smaller IFDs, so
the fix is our own IFD walk or an upstream contribution. The ladder is
written now so that fixing it is a decoder change, not a change to every
caller. Recorded in milestone-v0.1 risks.
Preview.downscale_to bounds memory: a 5472x3648 RGBA preview is 79.8MB,
which exhausts a phone's budget after a handful of images. Box-filtered
so downscaled thumbnails do not alias.
Also fixed a RefCell double-borrow that panicked on first navigation —
`*x.borrow_mut() = *x.borrow() + 1` holds both borrows at once. Verified
with 10,000 programmatic navigations.
58 tests passing. Traceability 20.3% (29/143).
Establishes the v0.1 foundations on both platforms:
- dr-types: SourceRef (never a filesystem path — Android SAF has none),
Format, Availability, Validator with ETag quote normalisation
- dr-gpu: wgpu device, compute pass writing a storage texture, resize
- dr-ui: Slint shell with FR-UI-1 adaptive layout, computed in Rust to
avoid a binding loop
- docker/android: pinned toolchain, verified producing API 28 ARM binaries
Measured the cost of the temporary CPU readback path (dr-gpu bench):
compute is 0.06-0.28ms across sizes while readback is 0.63-7.43ms, so
readback is 90-96% of frame time and scales with area. Recorded in
ARCH §6.1 — this is why spike S1 is the priority.
Mitigations pending S1: reuse the staging buffer, apply at most one
resize per frame, and cap render resolution at 2048 on the long edge.
10 tests passing; core crates cross-compile for aarch64-linux-android.
dtourolle