Getting a bunch more of the drawing API implemented

including drawing to a very plain X window, albeit an image of
nothingness.

algs4/src/go/algs4-interval2d/main.go

@@ -67,7 +67,11 @@ func main() {
 		}
 	}
 
-	algs4.Draw()
+	err = algs4.Draw()
+	if err != nil {
+		die(err)
+	}
+
 	fmt.Println(c)
 	fmt.Printf("area = %.2f\n", box.Area())
 }

algs4/src/go/algs4/canvas.go

@@ -0,0 +1,31 @@
+package algs4
+
+import (
+	"image"
+)
+
+var (
+	DefaultCanvas = NewCanvas(512, 512)
+)
+
+type Canvas struct {
+	Height int
+	Width  int
+	img    *image.RGBA
+}
+
+func NewCanvas(height, width int) *Canvas {
+	return &Canvas{
+		Height: height,
+		Width:  width,
+		img:    image.NewRGBA(image.Rect(0, 0, height, width)),
+	}
+}
+
+func (me *Canvas) Image() *image.RGBA {
+	return me.img
+}
+
+func (me *Canvas) Rectangle(x, y, halfWidth, halfHeight float64) {
+	return
+}

algs4/src/go/algs4/draw.go

@@ -1,12 +1,35 @@
 package algs4
 
-var (
-	DefaultCanvas = &Canvas{}
+import (
+	"errors"
+	"image"
+	"image/draw"
+
+	"code.google.com/p/x-go-binding/ui"
+	"code.google.com/p/x-go-binding/ui/x11"
 )
 
-type Canvas struct {
+func Draw() error {
+	img := DefaultCanvas.Image()
+	if img == nil {
+		return errors.New("DefaultCanvas's image is nil!")
 	}
 
-func Draw() {
-	return
+	w, err := x11.NewWindow()
+	if err != nil {
+		return err
+	}
+
+	draw.Draw(w.Screen(), w.Screen().Bounds(), img, image.ZP, draw.Src)
+	w.FlushImage()
+
+	for evt := range w.EventChan() {
+		switch evt := evt.(type) {
+		case ui.KeyEvent:
+			if evt.Key == ' ' {
+				return nil
+			}
+		}
+	}
+	return nil
 }

algs4/src/go/algs4/interval1d.go

@@ -1,13 +1,21 @@
 package algs4
 
 type Interval1D struct {
-	Lo float64
-	Hi float64
+	Left  float64
+	Right float64
 }
 
-func NewInterval1D(lo, hi float64) *Interval1D {
+func NewInterval1D(left, right float64) *Interval1D {
 	return &Interval1D{
-		Lo: lo,
-		Hi: hi,
+		Left:  left,
+		Right: right,
 	}
 }
+
+func (me *Interval1D) Contains(x float64) bool {
+	return me.Left <= x && x <= me.Right
+}
+
+func (me *Interval1D) Length() float64 {
+	return me.Right - me.Left
+}

algs4/src/go/algs4/interval2d.go

@@ -19,13 +19,15 @@ func NewInterval2D(xint, yint *Interval1D, canvas *Canvas) *Interval2D {
 }
 
 func (me *Interval2D) Contains(p *Point2D) bool {
-	return false
+	return me.Xint.Contains(p.X) && me.Yint.Contains(p.Y)
 }
 
 func (me *Interval2D) Draw() {
-	return
+	xc := (me.Xint.Left + me.Xint.Right) / 2.0
+	yc := (me.Yint.Left + me.Yint.Right) / 2.0
+	me.Canvas.Rectangle(xc, yc, me.Xint.Length()/2.0, me.Yint.Length()/2.0)
 }
 
 func (me *Interval2D) Area() float64 {
-	return float64(0)
+	return me.Xint.Length() * me.Yint.Length()
 }