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package main
import (
"errors"
"fmt"
"image"
"image/png"
"io"
"math"
"golang.org/x/image/draw"
glPng "gitlab.com/gitlab-org/gitlab/workhorse/cmd/gitlab-resize-image/png"
_ "image/jpeg"
)
// Image holds the source image, requested width and functionality to encode
type Image struct {
Source image.Image
RequestedWidth int
}
// NewImage returns a new instance of Image{}
func NewImage(requestedWidth int, r io.Reader) (Image, error) {
i := Image{RequestedWidth: requestedWidth}
if requestedWidth <= 0 {
return i, errors.New("requestedWidth needs to be > 0")
}
imgReader, err := glPng.NewReader(r)
if err != nil {
return i, fmt.Errorf("construct PNG reader: %w", err)
}
src, _, err := image.Decode(imgReader)
if err != nil {
return i, fmt.Errorf("decode: %w", err)
}
i.Source = src
return i, nil
}
// Encode writes a resized and scaled image, typically to os.Stdout
func (i Image) Encode(w io.Writer) error {
ratio := (float64)(i.Source.Bounds().Max.Y) / (float64)(i.Source.Bounds().Max.X)
height := int(math.Round(float64(i.RequestedWidth) * ratio))
dst := image.NewRGBA(image.Rect(0, 0, i.RequestedWidth, height))
draw.ApproxBiLinear.Scale(dst, dst.Rect, i.Source, i.Source.Bounds(), draw.Over, nil)
return png.Encode(w, dst)
}
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