sample.go

type Drawer interface {
	DrawTo(image.Image)
}
type Line struct {
	color Color
	a     Point
	b     Point
}

func (d Line) DrawTo(bg image.Image) {}

type Triangle struct {
	color Color
	fill  Color
	a     Point
	b     Point
	c     Point
}

func (d Triangle) DrawTo(bg image.Image) {}

type Fill struct {
	color Color
}

func (d Fill) DrawTo(bg image.Image) {}
func paintingLoop(img image.Image, ch chan Drawer) {
	// shorthand for a loop over receiving over
	// a channel
	for msg := range ch {
		msg.DrawTo(img)
	}
}
func drawThingy(ch chan Drawer) {
	ch <- Line{color: Red, a: Point{x: 0, y: 0}, b: Point{x: 1, y: 1}}
	ch <- Background{color: Blue}
}

func main() {
	// do some setup
	ch := make(chan Drawer, 100)
	// Create out destination image
	var img = image.NewNRGBA(image.Rectangle(100, 100))
	// Creates a goroutine which will handle the
	// event loop
	go func() {
		// create the window, etc
		paintingLoop(ch, img)
	}()
	drawThingy(ch)
	// Close when done.
	close(ch)
	// TODO: Add a channel to indicate image is done
}