func rescale(im image.Image, opts *DecodeOpts, swapDimensions bool) image.Image {
mw, mh := opts.MaxWidth, opts.MaxHeight
mwf, mhf := opts.ScaleWidth, opts.ScaleHeight
b := im.Bounds()
// only do downscaling, otherwise just serve the original image
if !opts.wantRescale(b, swapDimensions) {
return im
}
if swapDimensions {
mw, mh = mh, mw
}
// ScaleWidth and ScaleHeight overrule MaxWidth and MaxHeight
if mwf > 0.0 && mwf <= 1 {
mw = int(mwf * float32(b.Dx()))
}
if mhf > 0.0 && mhf <= 1 {
mh = int(mhf * float32(b.Dy()))
}
// If it's gigantic, it's more efficient to downsample first
// and then resize; resizing will smooth out the roughness.
// (trusting the moustachio guys on that one).
if b.Dx() > mw*2 || b.Dy() > mh*2 {
w, h := ScaledDimensions(b.Dx(), b.Dy(), mw*2, mh*2)
im = resize.ResampleInplace(im, b, w, h)
return resize.HalveInplace(im)
}
mw, mh = ScaledDimensions(b.Dx(), b.Dy(), mw, mh)
return resize.Resize(im, b, mw, mh)
}
// rescale resizes im in-place to the dimensions sw x sh, overwriting the
// existing pixel data. It is up to the caller to ensure sw & sh maintain the
// aspect ratio of im.
func rescale(im image.Image, sw, sh int) image.Image {
b := im.Bounds()
w, h := b.Dx(), b.Dy()
if sw == w && sh == h {
return im
}
// If it's gigantic, it's more efficient to downsample first
// and then resize; resizing will smooth out the roughness.
// (trusting the moustachio guys on that one).
if w > sw*2 && h > sh*2 {
im = resize.ResampleInplace(im, b, sw*2, sh*2)
return resize.HalveInplace(im)
}
return resize.Resize(im, b, sw, sh)
}