// decoder reads an image from r and modifies the image as defined by opts.
// swapDimensions indicates the decoded image will be rotated after being
// returned, and when interpreting opts, the post-rotation dimensions should
// be considered.
// The decoded image is returned in im. The registered name of the decoder
// used is returned in format. If the image was not successfully decoded, err
// will be non-nil. If the decoded image was made smaller, needRescale will
// be true.
func decode(r io.Reader, opts *DecodeOpts, swapDimensions bool) (im image.Image, format string, err error, needRescale bool) {
if opts == nil {
// Fall-back to normal decode.
im, format, err = image.Decode(r)
return im, format, err, false
}
var buf bytes.Buffer
tr := io.TeeReader(r, &buf)
ic, format, err := image.DecodeConfig(tr)
if err != nil {
return nil, "", err, false
}
mr := io.MultiReader(&buf, r)
b := image.Rect(0, 0, ic.Width, ic.Height)
sw, sh, needRescale := opts.rescaleDimensions(b, swapDimensions)
if !needRescale {
im, format, err = image.Decode(mr)
return im, format, err, false
}
imageDebug(fmt.Sprintf("Resizing from %dx%d -> %dx%d", ic.Width, ic.Height, sw, sh))
if format == "cr2" {
// Replace mr with an io.Reader to the JPEG thumbnail embedded in a
// CR2 image.
if mr, err = cr2.NewReader(mr); err != nil {
return nil, "", err, false
}
format = "jpeg"
}
if format == "jpeg" && fastjpeg.Available() {
factor := fastjpeg.Factor(ic.Width, ic.Height, sw, sh)
if factor > 1 {
var buf bytes.Buffer
tr := io.TeeReader(mr, &buf)
im, err = fastjpeg.DecodeDownsample(tr, factor)
switch err.(type) {
case fastjpeg.DjpegFailedError:
log.Printf("Retrying with jpeg.Decode, because djpeg failed with: %v", err)
im, err = jpeg.Decode(io.MultiReader(&buf, mr))
case nil:
// fallthrough to rescale() below.
default:
return nil, format, err, false
}
return rescale(im, sw, sh), format, err, true
}
}
// Fall-back to normal decode.
im, format, err = image.Decode(mr)
if err != nil {
return nil, "", err, false
}
return rescale(im, sw, sh), format, err, needRescale
}
func decodeDownsample(factor int) decodeFunc {
return func(r io.Reader) (image.Image, string, error) {
im, err := fastjpeg.DecodeDownsample(r, factor)
return im, "jpeg", err
}
}