transform.go

// 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"
	"fmt"
	"image"
	_ "image/gif" // register gif format
	"image/jpeg"
	"image/png"
	"math"

	"github.com/disintegration/imaging"
	"golang.org/x/image/tiff"   // register tiff format
	_ "golang.org/x/image/webp" // register webp format
	"willnorris.com/go/gifresize"
)

// 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.transform() {
		// 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
	}

	// encode webp and tiff as jpeg by default
	if format == "tiff" || format == "webp" {
		format = "jpeg"
	}

	if opt.Format != "" {
		format = opt.Format
	}

	// transform and encode image
	buf := new(bytes.Buffer)
	switch format {
	case "gif":
		fn := func(img image.Image) image.Image {
			return transformImage(img, opt)
		}
		err = gifresize.Process(buf, bytes.NewReader(img), fn)
		if err != nil {
			return nil, err
		}
	case "jpeg":
		quality := opt.Quality
		if quality == 0 {
			quality = defaultQuality
		}

		m = transformImage(m, opt)
		err = jpeg.Encode(buf, m, &jpeg.Options{Quality: quality})
		if err != nil {
			return nil, err
		}
	case "png":
		m = transformImage(m, opt)
		err = png.Encode(buf, m)
		if err != nil {
			return nil, err
		}
	case "tiff":
		m = transformImage(m, opt)
		err = tiff.Encode(buf, m, &tiff.Options{tiff.Deflate, true})
		if err != nil {
			return nil, err
		}
	default:
		return nil, fmt.Errorf("unsupported format: %v", format)
	}

	return buf.Bytes(), nil
}

// evaluateFloat interprets the option value f. If f is between 0 and 1, it is
// interpreted as a percentage of max, otherwise it is treated as an absolute
// value.  If f is less than 0, 0 is returned.
func evaluateFloat(f float64, max int) int {
	if 0 < f && f < 1 {
		return int(float64(max) * f)
	}
	if f < 0 {
		return 0
	}
	return int(f)
}

// resizeParams determines if the image needs to be resized, and if so, the
// dimensions to resize to.
func resizeParams(m image.Image, opt Options) (w, h int, resize bool) {
	// 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
	w = evaluateFloat(opt.Width, imgW)
	h = evaluateFloat(opt.Height, imgH)

	// never resize larger than the original image unless specifically allowed
	if !opt.ScaleUp {
		if w > imgW {
			w = imgW
		}
		if h > imgH {
			h = imgH
		}
	}

	// if requested width and height match the original, skip resizing
	if (w == imgW || w == 0) && (h == imgH || h == 0) {
		return 0, 0, false
	}

	return w, h, true
}

// cropParams calculates crop rectangle parameters to keep it in image bounds
func cropParams(m image.Image, opt Options) (x0, y0, x1, y1 int, crop bool) {
	if opt.CropX == 0 && opt.CropY == 0 && opt.CropWidth == 0 && opt.CropHeight == 0 {
		return 0, 0, 0, 0, false
	}

	// width and height of image
	imgW := m.Bounds().Max.X - m.Bounds().Min.X
	imgH := m.Bounds().Max.Y - m.Bounds().Min.Y

	// top left coordinate of crop
	x0 = evaluateFloat(math.Abs(opt.CropX), imgW)
	if opt.CropX < 0 {
		x0 = imgW - x0
	}
	y0 = evaluateFloat(math.Abs(opt.CropY), imgH)
	if opt.CropY < 0 {
		y0 = imgH - y0
	}

	// width and height of crop
	w := evaluateFloat(opt.CropWidth, imgW)
	if w == 0 {
		w = imgW
	}
	h := evaluateFloat(opt.CropHeight, imgH)
	if h == 0 {
		h = imgH
	}

	if x0 == 0 && y0 == 0 && w == imgW && h == imgH {
		return 0, 0, 0, 0, false
	}

	// bottom right coordinate of crop
	x1 = x0 + w
	if x1 > imgW {
		x1 = imgW
	}
	y1 = y0 + h
	if y1 > imgH {
		y1 = imgH
	}

	return x0, y0, x1, y1, true
}

// transformImage modifies the image m based on the transformations specified
// in opt.
func transformImage(m image.Image, opt Options) image.Image {
	// crop if needed
	if x0, y0, x1, y1, crop := cropParams(m, opt); crop {
		m = imaging.Crop(m, image.Rect(x0, y0, x1, y1))
	}
	// resize if needed
	if w, h, resize := resizeParams(m, opt); resize {
		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)
			}
		}
	}

	// rotate
	switch opt.Rotate {
	case 90:
		m = imaging.Rotate90(m)
	case 180:
		m = imaging.Rotate180(m)
	case 270:
		m = imaging.Rotate270(m)
	}

	// flip
	if opt.FlipVertical {
		m = imaging.FlipV(m)
	}
	if opt.FlipHorizontal {
		m = imaging.FlipH(m)
	}

	return m
}