Bring over X canvas package

x/canvas/line.go

@@ -0,0 +1,95 @@
+package xcanvas
+
+import "image"
+import "github.com/jezek/xgbutil/xgraphics"
+
+// TODO: clip the line to the bounds
+func (this *pen) line  (
+	c      xgraphics.BGRA,
+	min    image.Point,
+	max    image.Point,
+) {
+	context := linePlottingContext {
+		plottingContext: plottingContext {
+			image:  this.image,
+			color:  c,
+			weight: this.weight,
+		},
+		min: min,
+		max: max,
+	}
+
+	if abs(max.Y - min.Y) < abs(max.X - min.X) {
+		if max.X < min.X { context.swap() }
+		context.lineLow()
+
+	} else {
+		if max.Y < min.Y { context.swap() }
+		context.lineHigh()
+	}
+}
+
+type linePlottingContext struct {
+	plottingContext
+	min image.Point
+	max image.Point
+}
+
+func (context *linePlottingContext) swap () {
+	temp := context.max
+	context.max = context.min
+	context.min = temp
+}
+
+func (context linePlottingContext) lineLow () {
+	deltaX := context.max.X - context.min.X
+	deltaY := context.max.Y - context.min.Y
+	yi     := 1
+
+	if deltaY < 0 {
+		yi      = -1
+		deltaY *= -1
+	}
+
+	D := (2 * deltaY) - deltaX
+	point := context.min
+
+	for ; point.X < context.max.X; point.X ++ {
+		context.plot(point)
+		if D > 0 {
+			D += 2 * (deltaY - deltaX)
+			point.Y += yi
+		} else {
+			D += 2 * deltaY
+		}
+	}
+}
+
+func (context linePlottingContext) lineHigh () {
+	deltaX := context.max.X - context.min.X
+	deltaY := context.max.Y - context.min.Y
+	xi     := 1
+
+	if deltaX < 0 {
+		xi      = -1
+		deltaX *= -1
+	}
+
+	D := (2 * deltaX) - deltaY
+	point := context.min
+
+	for ; point.Y < context.max.Y; point.Y ++ {
+		context.plot(point)
+		if D > 0 {
+			point.X += xi
+			D += 2 * (deltaX - deltaY)
+		} else {
+			D += 2 * deltaX
+		}
+	}
+}
+
+func abs (n int) int {
+	if n < 0 { n *= -1}
+	return n
+}