forked from laher/imageproxy
/
transform.go
131 lines (114 loc) · 2.87 KB
/
transform.go
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// Copyright 2013 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package imageproxy
import (
"bytes"
"image"
"image/gif"
"image/jpeg"
"image/png"
"github.com/disintegration/imaging"
)
// default compression quality of resized jpegs
const defaultQuality = 95
// resample filter used when resizing images
var resampleFilter = imaging.Lanczos
// Transform the provided image. img should contain the raw bytes of an
// encoded image in one of the supported formats (gif, jpeg, or png). The
// bytes of a similarly encoded image is returned.
func Transform(img []byte, opt Options) ([]byte, error) {
if opt == emptyOptions {
// bail if no transformation was requested
return img, nil
}
// decode image
m, format, err := image.Decode(bytes.NewReader(img))
if err != nil {
return nil, err
}
m = transformImage(m, opt)
// encode image
buf := new(bytes.Buffer)
switch format {
case "gif":
gif.Encode(buf, m, nil)
case "jpeg":
quality := opt.Quality
if quality == 0 {
quality = defaultQuality
}
jpeg.Encode(buf, m, &jpeg.Options{Quality: quality})
case "png":
png.Encode(buf, m)
}
return buf.Bytes(), nil
}
// transformImage modifies the image m based on the transformations specified
// in opt.
func transformImage(m image.Image, opt Options) image.Image {
// convert percentage width and height values to absolute values
imgW := m.Bounds().Max.X - m.Bounds().Min.X
imgH := m.Bounds().Max.Y - m.Bounds().Min.Y
var w, h int
if 0 < opt.Width && opt.Width < 1 {
w = int(float64(imgW) * opt.Width)
} else if opt.Width < 0 {
w = 0
} else {
w = int(opt.Width)
}
if 0 < opt.Height && opt.Height < 1 {
h = int(float64(imgH) * opt.Height)
} else if opt.Height < 0 {
h = 0
} else {
h = int(opt.Height)
}
// never resize larger than the original image
if w > imgW {
w = imgW
}
if h > imgH {
h = imgH
}
// resize
if w != 0 || h != 0 {
if opt.Fit {
m = imaging.Fit(m, w, h, resampleFilter)
} else {
if w == 0 || h == 0 {
m = imaging.Resize(m, w, h, resampleFilter)
} else {
m = imaging.Thumbnail(m, w, h, resampleFilter)
}
}
}
// flip
if opt.FlipVertical {
m = imaging.FlipV(m)
}
if opt.FlipHorizontal {
m = imaging.FlipH(m)
}
// rotate
switch opt.Rotate {
case 90:
m = imaging.Rotate90(m)
case 180:
m = imaging.Rotate180(m)
case 270:
m = imaging.Rotate270(m)
}
return m
}