gopl-zh.github.com/vendor/gopl.io/ch8/thumbnail/thumbnail.go

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2015-12-09 07:45:11 +00:00
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 234.
// The thumbnail package produces thumbnail-size images from
// larger images. Only JPEG images are currently supported.
package thumbnail
import (
"fmt"
"image"
"image/jpeg"
"io"
"os"
"path/filepath"
"strings"
)
// Image returns a thumbnail-size version of src.
func Image(src image.Image) image.Image {
// Compute thumbnail size, preserving aspect ratio.
xs := src.Bounds().Size().X
ys := src.Bounds().Size().Y
width, height := 128, 128
if aspect := float64(xs) / float64(ys); aspect < 1.0 {
width = int(128 * aspect) // portrait
} else {
height = int(128 / aspect) // landscape
}
xscale := float64(xs) / float64(width)
yscale := float64(ys) / float64(height)
dst := image.NewRGBA(image.Rect(0, 0, width, height))
// a very crude scaling algorithm
for x := 0; x < width; x++ {
for y := 0; y < height; y++ {
srcx := int(float64(x) * xscale)
srcy := int(float64(y) * yscale)
dst.Set(x, y, src.At(srcx, srcy))
}
}
return dst
}
// ImageStream reads an image from r and
// writes a thumbnail-size version of it to w.
func ImageStream(w io.Writer, r io.Reader) error {
src, _, err := image.Decode(r)
if err != nil {
return err
}
dst := Image(src)
return jpeg.Encode(w, dst, nil)
}
// ImageFile2 reads an image from infile and writes
// a thumbnail-size version of it to outfile.
func ImageFile2(outfile, infile string) (err error) {
in, err := os.Open(infile)
if err != nil {
return err
}
defer in.Close()
out, err := os.Create(outfile)
if err != nil {
return err
}
if err := ImageStream(out, in); err != nil {
out.Close()
return fmt.Errorf("scaling %s to %s: %s", infile, outfile, err)
}
return out.Close()
}
// ImageFile reads an image from infile and writes
// a thumbnail-size version of it in the same directory.
// It returns the generated file name, e.g. "foo.thumb.jpeg".
func ImageFile(infile string) (string, error) {
ext := filepath.Ext(infile) // e.g., ".jpg", ".JPEG"
outfile := strings.TrimSuffix(infile, ext) + ".thumb" + ext
return outfile, ImageFile2(outfile, infile)
}