Whether an effect works from the loaded photographs is now part of the
declarative plug-in contract, next to params(): Effect::needsSources()
defaults to true, and blur — which only softens what it is handed — says
no and blurs an empty canvas when given nothing.
Only the first stage of a cascade ever sees the sources, so
chainNeedsSources() just asks the first stage. Both front-ends gate on
that instead of on "are there any images": the CLI only refuses an empty
batch when the chain wants one, and the interface renders a blur-led
chain with no images loaded, saying whichever thing is actually missing.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Fills the canvas from one source, tiling it when it is smaller, then
applies a separable box blur repeated `passes` times to approximate a
gaussian. Params: radius, passes, direction and first_source, so the CLI
flags and the GUI widgets come out of the ParamSpecs as usual.
All random values (source index and crop offset) are drawn serially
before the parallel pixel work, so a seed reproduces the image exactly;
the box window clamps at both ends and the radius is clamped to the
canvas so an oversized radius cannot read out of bounds.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
