Add convert to imgutil

1 files changed, 149 insertions, 0 deletions

diff --git a/convert.go b/convert.go
new file mode 100644
index 0000000..d0523ba
--- /dev/null
+++ b/convert.go
@@ -0,0 +1,149 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
+	"os"
+	"strings"
+
+	"golang.org/x/image/bmp"
+	"golang.org/x/image/draw"
+	"golang.org/x/image/tiff"
+	_ "golang.org/x/image/webp"
+)
+
+var (
+	x       = flag.Int("x", 0, "new image width")
+	y       = flag.Int("y", 0, "new image height")
+	stretch = flag.Bool("stretch", false, "if resizing, whether to stretch the image rather than cropping (the default)")
+	format  = flag.String("format", "", "output image format, default is to use the file extension")
+)
+
+func load(filename string) (image.Image, error) {
+	file := os.Stdin
+	if filename != "-" {
+		var err error
+		file, err = os.Open(filename)
+		if err != nil {
+			return nil, err
+		}
+		defer file.Close()
+	}
+
+	img, _, err := image.Decode(file)
+	if err != nil {
+		return nil, fmt.Errorf("decode %q: %s", filename, err)
+	}
+
+	return img, nil
+}
+
+func divRound(n, d int) int {
+	return (n + d/2) / d
+}
+
+func resize(img image.Image) image.Image {
+	x, y := *x, *y
+	if x == 0 {
+		x = divRound(y*img.Bounds().Dx(), img.Bounds().Dy())
+	}
+	if y == 0 {
+		y = divRound(x*img.Bounds().Dy(), img.Bounds().Dx())
+	}
+	output := image.NewRGBA64(image.Rect(0, 0, x, y))
+	srcRect := img.Bounds()
+	if !*stretch {
+		if img.Bounds().Dx()*y >= img.Bounds().Dy()*x {
+			scaledX := divRound(img.Bounds().Dy()*x, y)
+			xOffset := (img.Bounds().Dx() - scaledX) / 2
+			srcRect.Min.X += xOffset
+			srcRect.Max.X = srcRect.Min.X + scaledX
+		} else {
+			scaledY := divRound(img.Bounds().Dx()*y, x)
+			yOffset := (img.Bounds().Dy() - scaledY) / 2
+			srcRect.Min.Y += yOffset
+			srcRect.Max.Y = srcRect.Min.Y + scaledY
+		}
+	}
+	draw.CatmullRom.Scale(output, output.Bounds(), img, srcRect, draw.Src, nil)
+	return output
+}
+
+func run() error {
+	args := flag.Args()
+	if len(args) != 2 {
+		return errors.New("usage: convert input-file output-file")
+	}
+	inputFileName, outputFileName := args[0], args[1]
+
+	ext := *format
+	if ext == "" {
+		n := strings.LastIndex(outputFileName, ".")
+		if n < 0 {
+			return errors.New("unknown output file extension")
+		}
+		ext = outputFileName[n+1:]
+	}
+	switch ext {
+	case "gif", "jpeg", "jpg", "png", "bmp", "tiff":
+	default:
+		return fmt.Errorf("unknown output file extension %q", ext)
+	}
+
+	input, err := load(inputFileName)
+	if err != nil {
+		return err
+	}
+
+	if *x != 0 || *y != 0 {
+		input = resize(input)
+	}
+
+	outputFile, err := os.Create(outputFileName)
+	if err != nil {
+		return err
+	}
+	defer outputFile.Close()
+	switch ext {
+	case "gif":
+		err = gif.Encode(outputFile, input, nil)
+	case "jpeg", "jpg":
+		err = jpeg.Encode(outputFile, input, &jpeg.Options{Quality: 100})
+	case "png":
+		err = png.Encode(outputFile, input)
+	case "bmp":
+		err = bmp.Encode(outputFile, input)
+	case "tiff":
+		err = tiff.Encode(outputFile, input, nil)
+	}
+	if err != nil {
+		return err
+	}
+	return outputFile.Close()
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprint(os.Stderr, `Usage: convert input-file output-file
+Supported formats:
+  png
+  jpeg
+  bmp
+  tiff
+  webp (input only)
+
+`)
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	if err := run(); err != nil {
+		fmt.Fprintf(os.Stderr, "convert: %s\n", err)
+		os.Exit(1)
+	}
+}