87 lines
2.2 KiB
Go
87 lines
2.2 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 234.
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// The thumbnail package produces thumbnail-size images from
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// larger images. Only JPEG images are currently supported.
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package thumbnail
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import (
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"fmt"
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"image"
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"image/jpeg"
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"io"
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"os"
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"path/filepath"
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"strings"
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)
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// Image returns a thumbnail-size version of src.
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func Image(src image.Image) image.Image {
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// Compute thumbnail size, preserving aspect ratio.
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xs := src.Bounds().Size().X
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ys := src.Bounds().Size().Y
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width, height := 128, 128
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if aspect := float64(xs) / float64(ys); aspect < 1.0 {
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width = int(128 * aspect) // portrait
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} else {
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height = int(128 / aspect) // landscape
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}
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xscale := float64(xs) / float64(width)
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yscale := float64(ys) / float64(height)
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dst := image.NewRGBA(image.Rect(0, 0, width, height))
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// a very crude scaling algorithm
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for x := 0; x < width; x++ {
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for y := 0; y < height; y++ {
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srcx := int(float64(x) * xscale)
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srcy := int(float64(y) * yscale)
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dst.Set(x, y, src.At(srcx, srcy))
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}
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}
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return dst
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}
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// ImageStream reads an image from r and
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// writes a thumbnail-size version of it to w.
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func ImageStream(w io.Writer, r io.Reader) error {
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src, _, err := image.Decode(r)
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if err != nil {
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return err
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}
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dst := Image(src)
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return jpeg.Encode(w, dst, nil)
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}
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// ImageFile2 reads an image from infile and writes
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// a thumbnail-size version of it to outfile.
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func ImageFile2(outfile, infile string) (err error) {
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in, err := os.Open(infile)
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if err != nil {
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return err
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}
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defer in.Close()
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out, err := os.Create(outfile)
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if err != nil {
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return err
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}
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if err := ImageStream(out, in); err != nil {
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out.Close()
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return fmt.Errorf("scaling %s to %s: %s", infile, outfile, err)
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}
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return out.Close()
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}
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// ImageFile reads an image from infile and writes
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// a thumbnail-size version of it in the same directory.
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// It returns the generated file name, e.g. "foo.thumb.jpeg".
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func ImageFile(infile string) (string, error) {
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ext := filepath.Ext(infile) // e.g., ".jpg", ".JPEG"
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outfile := strings.TrimSuffix(infile, ext) + ".thumb" + ext
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return outfile, ImageFile2(outfile, infile)
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}
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