Extract the image shape to use with the speedata Publisher

main.go

package main

import (
	"encoding/xml"
	"fmt"
	"image"
	"image/color"
	"log"
	"os/exec"

	_ "image/png"
)

type Imageinfo struct {
	XMLName xml.Name `xml:"imageinfo"`
	CellsX  int      `xml:"cells_x"`
	CellsY  int      `xml:"cells_y"`
	Segment []Segment
}
type Segment struct {
	XMLName xml.Name `xml:"segment"`
	X1      int      `xml:"x1,attr"`
	X2      int      `xml:"x2,attr"`
	Y1      int      `xml:"y1,attr"`
	Y2      int      `xml:"y2,attr"`
}

func isBlack(col color.Color) bool {
	switch x := col.(type) {
	case color.Gray16:
		return x.Y < 0xfa00
	default:
		log.Fatal("Unknown type for color %#v", col)
	}

	return true
}

func main() {
	imagepath := "pocketwatch.pdf"
	// Run imagemagick to get a max(40x40) pixel image
	cmd := exec.Command("convert", imagepath, "-monochrome", "-resize", "40x40", "png:-")
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		log.Fatal(err)
	}

	err = cmd.Start()
	if err != nil {
		log.Fatal(err)
	}
	img, _, err := image.Decode(stdout)
	if err != nil {
		log.Fatal(err)
	}
	err = cmd.Wait()
	if err != nil {
		log.Fatal(err)
	}

	// Now construct the XML
	bounds := img.Bounds()
	ii := Imageinfo{}
	ii.CellsX = bounds.Dx()
	ii.CellsY = bounds.Dy()
	for y := 0; y < bounds.Dy(); y++ {
		s := Segment{}
		hasBlackPixel := false
		for x := 0; x < bounds.Dx(); x++ {
			s.Y1 = y + 1
			s.Y2 = y + 1
			if isBlack(img.At(x, y)) {
				hasBlackPixel = true
				if s.X1 == 0 {
					s.X1 = x + 1
				}
				s.X2 = x + 1
			}
		}
		if hasBlackPixel {
			ii.Segment = append(ii.Segment, s)
		}
	}
	b, err := xml.MarshalIndent(ii, "", "  ")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(string(b))
}