A folder of RAW took the page down. The catalogue reads four frames at once —
that is what makes a roll land quickly, and for a JPEG it is free — but a RAW is
not read by this page at all: it is handed to libraw-wasm, which opens it inside
a worker of its own, and that worker is built with a quarter of a gigabyte of
linear memory (emscripten's shared memory, 256MB, instantiated per instance) and
the whole frame is copied into it. Four of those at once, on frames of 22.6MB,
is past what a renderer is given before a single tile is drawn, and the page goes
with it — which is the crash this answers.
One open at a time now, whoever asks for it: the gate wraps the read of a RAW and
nothing else, so the frames around the one being opened still have their bytes
read off the disk, their decodes run and their tiles encoded side by side. Only
the open queues. A folder of JPEGs never touches the gate and keeps all four
lanes.
The tile also stops asking the decoder a question the bytes answer. A JPEG — and
the preview a camera writes inside a RAW is one — carries its frame size in its
own header, in the first few hundred bytes the read already holds for the date.
`jpegSize` reads it there, and `tile` is handed the size instead of decoding the
whole frame a second time only to learn which edge is long. `jpegSize` existed
for exactly this and had no caller; it has one now.
Verified:
- library-check.mjs, scan-nav-check.mjs, roll-walk-check.mjs all pass against the
built bundle — the catalogue still reads a roll, a RAW still becomes a tile off
its own preview, a frame still says where it was shot, an interrupted reading
still goes on by itself.
- A stand-in folder answered `showDirectoryPicker`, 48 frames of 22.6MB, resident
memory of the whole browser process tree sampled every 150ms:
- before: 4 frames read at once, peak RSS 1335MB, 565MB before the roll was
picked, 12s, 48 tiles, no error;
- after: 1 frame read at once, peak RSS 1180MB, 32s, 48 tiles, no error.
The 2.6× on the clock is mostly the harness: its `getFile` copies 22.6MB per
frame, so serialising the open serialises that copy too. A real folder pays a
disk read and an open in sequence instead.
- 200 frames of 8.5MB JPEG, same harness: peak 1713MB, 4 at a time, 200 tiles,
no error — the JPEG path is untouched by this commit.
ponytail: reading a RAW could skip LibRaw entirely — the camera's preview is a
plain JPEG and could be cut out of the head of the file this page has already
read. Probed on four samples: RW2 carries a 1920×1280 preview at 54KB, NEF one at
6016×4016 of 1.08MB, but DNG has only 720×480 inside its first 4MB and RAF keeps
almost none, and picking the wrong segment risks a thumbnail for a tile. Not
worth it until a RAW that is neither DNG nor RAF is the common case. The JPEG
path still peaks high (1713MB over 200 frames) and that is `createImageBitmap`
decoding every 5472×3648 frame whole, at four lanes — an app that reads fewer at
once trades time for the same headroom, if a page that large is ever the crash
again.
Co-authored-by: PenguinHarness <noreply@penguin.local>
3dtours
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