fn cap_and_encode(img: RgbaImage, cap: i32) -> Option<CappedSprite>Expand description
Apply the size cap to a premultiplied sprite and encode it as a straight-alpha PNG.
cap <= 0, or a sprite already within it, is encoded at its source size. Resizing happens
while the pixels are still premultiplied — filtering straight alpha pulls the (zero) color
of transparent texels into the edges and leaves a dark fringe, and Lanczos3 overshoot has no
headroom to land in — which is the order the X11 XFixes path uses.