Initial commit

escpos/raster.go

@@ -0,0 +1,173 @@
+package escpos
+
+import (
+	"fmt"
+	"image"
+	"image/png"
+	"io"
+	"os"
+)
+
+func closestNDivisibleBy8(n int) int {
+	q := n / 8
+	n1 := q * 8
+
+	return n1
+}
+
+func PrintImage(imgFile string, w io.Writer) error {
+	image.RegisterFormat("png", "png", png.Decode, png.DecodeConfig)
+
+	width, height, pixels, err := getPixels(imgFile)
+
+	if err != nil {
+		return err
+	}
+
+	removeTransparency(&pixels)
+	makeGrayscale(&pixels)
+
+	printWidth := closestNDivisibleBy8(width)
+	printHeight := closestNDivisibleBy8(height)
+	bytes, _ := rasterize(printWidth, printHeight, &pixels)
+
+	imageHeader := []byte{0x1d, 0x76, 0x30, 0x00}
+	imageData := []byte{}
+	imageData = append(imageHeader,
+		byte((width>>3)&0xff),
+		byte(((width>>3)>>8)&0xff),
+		byte(height&0xff),
+		byte((height>>8)&0xff))
+	imageData = append(imageData, bytes...)
+
+	_, err = w.Write(imageData)
+
+	return err
+}
+
+func makeGrayscale(pixels *[][]pixel) {
+	height := len(*pixels)
+	width := len((*pixels)[0])
+
+	for y := 0; y < height; y++ {
+		row := (*pixels)[y]
+		for x := 0; x < width; x++ {
+			pixel := row[x]
+
+			luminance := (float64(pixel.R) * 0.299) + (float64(pixel.G) * 0.587) + (float64(pixel.B) * 0.114)
+			var value int
+			if luminance < 128 {
+				value = 0
+			} else {
+				value = 255
+			}
+
+			pixel.R = value
+			pixel.G = value
+			pixel.B = value
+
+			row[x] = pixel
+		}
+	}
+}
+
+func removeTransparency(pixels *[][]pixel) {
+	height := len(*pixels)
+	width := len((*pixels)[0])
+
+	for y := 0; y < height; y++ {
+		row := (*pixels)[y]
+		for x := 0; x < width; x++ {
+			pixel := row[x]
+
+			alpha := pixel.A
+			invAlpha := 255 - alpha
+
+			pixel.R = (alpha*pixel.R + invAlpha*255) / 255
+			pixel.G = (alpha*pixel.G + invAlpha*255) / 255
+			pixel.B = (alpha*pixel.B + invAlpha*255) / 255
+			pixel.A = 255
+
+			row[x] = pixel
+		}
+	}
+}
+
+func rasterize(printWidth int, printHeight int, pixels *[][]pixel) ([]byte, error) {
+	if printWidth%8 != 0 {
+		return nil, fmt.Errorf("printWidth must be a multiple of 8")
+	}
+
+	if printHeight%8 != 0 {
+		return nil, fmt.Errorf("printHeight must be a multiple of 8")
+	}
+
+	bytes := make([]byte, (printWidth*printHeight)>>3)
+
+	for y := 0; y < printHeight; y++ {
+		for x := 0; x < printWidth; x = x + 8 {
+			i := y*(printWidth>>3) + (x >> 3)
+			bytes[i] =
+				byte((getPixelValue(x+0, y, pixels) << 7) |
+					(getPixelValue(x+1, y, pixels) << 6) |
+					(getPixelValue(x+2, y, pixels) << 5) |
+					(getPixelValue(x+3, y, pixels) << 4) |
+					(getPixelValue(x+4, y, pixels) << 3) |
+					(getPixelValue(x+5, y, pixels) << 2) |
+					(getPixelValue(x+6, y, pixels) << 1) |
+					getPixelValue(x+7, y, pixels))
+		}
+	}
+
+	return bytes, nil
+}
+
+func getPixelValue(x int, y int, pixels *[][]pixel) int {
+	row := (*pixels)[y]
+	pixel := row[x]
+
+	if pixel.R > 0 {
+		return 0
+	}
+
+	return 1
+}
+
+func rgbaToPixel(r uint32, g uint32, b uint32, a uint32) pixel {
+	return pixel{int(r >> 8), int(g >> 8), int(b >> 8), int(a >> 8)}
+}
+
+type pixel struct {
+	R int
+	G int
+	B int
+	A int
+}
+
+func getPixels(imgFile string) (int, int, [][]pixel, error) {
+	infile, err := os.Open(imgFile)
+	if err != nil {
+		return 0, 0, nil, err
+	}
+	defer infile.Close()
+
+	img, _, err := image.Decode(infile)
+
+	if err != nil {
+		return 0, 0, nil, err
+	}
+
+	bounds := img.Bounds()
+	width, height := bounds.Max.X, bounds.Max.Y
+
+	var pixels [][]pixel
+	for y := 0; y < height; y++ {
+		var row []pixel
+		for x := 0; x < width; x++ {
+			row = append(row, rgbaToPixel(img.At(x, y).RGBA()))
+		}
+		pixels = append(pixels, row)
+	}
+
+	return width, height, pixels, nil
+}

go.mod

@@ -0,0 +1,3 @@
+module github.com/mugli/png2escpos
+
+go 1.12

png2escpos.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/mugli/png2escpos/escpos"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		showHelp()
+	}
+
+	imgFile := os.Args[1]
+	err := escpos.PrintImage(imgFile, os.Stdout)
+
+	if err != nil {
+		fmt.Println("Error printing image: %v", err)
+		os.Exit(1)
+	}
+}
+
+func showHelp() {
+	os.Exit(1)
+}