82 lines
1.7 KiB
Go
82 lines
1.7 KiB
Go
package main
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import (
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"image"
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"image/color"
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_ "image/gif"
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"image/jpeg"
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_ "image/png"
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"io"
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)
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func init() {
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thumbnailers = append(thumbnailers, &imageThumbnailer{})
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}
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type imageThumbnailer struct{}
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func (it *imageThumbnailer) CanHandle(ext string) bool {
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switch ext {
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case ".jpg", ".jpeg", ".png", ".gif":
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return true
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}
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return false
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}
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func (it *imageThumbnailer) Generate(src io.Reader, dst io.Writer, width int) error {
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img, _, err := image.Decode(src)
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if err != nil {
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return err
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}
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return jpeg.Encode(dst, resizeBox(img, width), &jpeg.Options{Quality: 80})
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}
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// resizeBox downsamples src to the requested width using a box filter.
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// Aspect ratio is preserved. Upscaling is a no-op (returns src unchanged).
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// Each source pixel is visited exactly once; alpha is discarded.
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func resizeBox(src image.Image, width int) image.Image {
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b := src.Bounds()
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srcW, srcH := b.Dx(), b.Dy()
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if srcW <= width {
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return src
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}
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dstW := width
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dstH := srcH * width / srcW
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if dstH < 1 {
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dstH = 1
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}
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dst := image.NewRGBA(image.Rect(0, 0, dstW, dstH))
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for y := 0; y < dstH; y++ {
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sy0 := y * srcH / dstH
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sy1 := (y + 1) * srcH / dstH
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if sy1 == sy0 {
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sy1 = sy0 + 1
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}
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for x := 0; x < dstW; x++ {
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sx0 := x * srcW / dstW
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sx1 := (x + 1) * srcW / dstW
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if sx1 == sx0 {
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sx1 = sx0 + 1
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}
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var r, g, bl, n uint64
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for sy := sy0; sy < sy1; sy++ {
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for sx := sx0; sx < sx1; sx++ {
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sr, sg, sb, _ := src.At(b.Min.X+sx, b.Min.Y+sy).RGBA()
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r += uint64(sr >> 8)
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g += uint64(sg >> 8)
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bl += uint64(sb >> 8)
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n++
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}
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}
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dst.SetRGBA(x, y, color.RGBA{
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R: uint8(r / n),
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G: uint8(g / n),
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B: uint8(bl / n),
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A: 255,
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})
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}
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}
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return dst
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}
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