Function minify 

pub fn minify(source: &Pixmap, width: u32, height: u32) -> Pixmap

source box-filtered down to width x height.

Every output texel is the unweighted mean of the half-open source rectangle it covers, computed on the premultiplied bytes the atlas stores — which is the space the samples are composited in, so averaging there is what keeps a partially transparent source from bleeding its colour outward.

Minification only: a request at or above the source’s own extent copies the texels straight across rather than inventing any, since a box filter has no magnification arm and the caller never asks for one (fit_extent only ever shrinks).