photo mosaic blog 17

.go

func combine(r image.Rectangle, c1, c2, c3, c4 <-chan image.Image) 
<-chan string {
    c := make(chan string)
    // start a goroutine
    go func() {
        var wg sync.WaitGroup
        img:= image.NewNRGBA(r)
        copy := func(dst draw.Image, r image.Rectangle, 
src image.Image, sp image.Point) {
            draw.Draw(dst, r, src, sp, draw.Src)
            wg.Done()
        }
        wg.Add(4)
        var s1, s2, s3, s4 image.Image
        var ok1, ok2, ok3, ok4 bool
        for  {
            select {
            case s1, ok1 = <-c1:
                go copy(img, s1.Bounds(), s1,
                    image.Point{r.Min.X, r.Min.Y})
            case s2, ok2 = <-c2:
                go copy(img, s2.Bounds(), s2, image.Point{r.Max.X / 2, r.Min.Y})
            case s3, ok3 = <-c3:
                go copy(img, s3.Bounds(), s3, image.Point{r.Min.X, r.Max.Y/2})
            case s4, ok4 = <-c4:
                go copy(img, s4.Bounds(), s4, image.Point{r.Max.X / 2, r.Max.Y / 2})
            }
            if (ok1 && ok2 && ok3 && ok4) {
                break
            }
        }
        // wait till all copy goroutines are complete
        wg.Wait()
        buf2 := new(bytes.Buffer)
        jpeg.Encode(buf2, newimage, nil)
        c <- base64.StdEncoding.EncodeToString(buf2.Bytes())
    }()
    return c
}