Scrollbar now displays scroll value

scrollbar.go

@@ -43,6 +43,7 @@ func newScrollbar (orient string) *Scrollbar {
 	this.OnMouseDown(this.handleMouseDown)
 	this.OnMouseUp(this.handleMouseUp)
 	this.OnMouseMove(this.handleMouseMove)
+	this.OnScroll(this.handleScroll)
 	theme.Apply(this.handle, theme.R("objects", "SliderHandle", orient))
 	theme.Apply(this,        theme.R("objects", "Slider", orient))
 	return this
@@ -65,10 +66,13 @@ func (this *Scrollbar) Link (box tomo.ContentBox) event.Cookie {
 }
 
 func (this *Scrollbar) handleLinkedContentBoundsChange () {
-	if this.layout.linked == 0 { return }
-	this.layout.value =
-		this.layout.contentPos() /
-		(this.layout.contentLength() - this.layout.viewportLength())
+	if this.layout.linked == nil { return }
+	trackLength := this.layout.contentLength() - this.layout.viewportLength()
+	if trackLength == 0 {
+		this.layout.value = 0
+	} else {
+		this.layout.value = this.layout.contentPos() / trackLength
+	}
 	this.SetLayout(this.layout)
 }
 
@@ -171,6 +175,13 @@ func (this *Scrollbar) handleMouseMove () {
 	this.drag()
 }
 
+func (this *Scrollbar) handleScroll (x, y float64) {
+	if this.layout.linked == nil { return }
+	this.layout.linked.ScrollTo (
+		this.layout.linked.ContentBounds().Min.
+		Add(image.Pt(int(x), int(y))))
+}
+
 func (this *Scrollbar) drag () {
 	pointer := this.MousePosition().Sub(this.dragOffset)
 	gutter  := this.InnerBounds()
@@ -234,18 +245,44 @@ func (this scrollbarLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 	handle := image.Rectangle { Max: boxes[0].MinimumSize() }
 	gutter := hints.Bounds
 
+	var gutterLength float64;
+	var handleMin    float64;
+	if this.vertical {
+		gutterLength = float64(gutter.Dy())
+		handleMin    = float64(handle.Dy())
+	} else {
+		gutterLength = float64(gutter.Dx())
+		handleMin    = float64(handle.Dx())
+	}
+
+	// calculate handle length
+	handleLength := gutterLength * this.viewportContentRatio()
+	if handleLength < handleMin { handleLength = handleMin }
+	if handleLength > gutterLength { handleLength = gutterLength }
+	if this.vertical {
+		handle.Max.Y = int(handleLength)
+	} else {
+		handle.Max.X = int(handleLength)
+	}
+
+	// calculate handle position
+	handlePosition := (gutterLength - handleLength) * this.value
+	var handleOffset image.Point
+	if this.vertical {
+		handleOffset = image.Pt(0, int(handlePosition))
+	} else {
+		handleOffset = image.Pt(int(handlePosition), 0)
+	}
+	handle = handle.Add(handleOffset).Add(gutter.Min)
+	
+	// place handle
+	boxes[0].SetBounds(handle)
 	
-	// TODO
-	// - apply (viewportContentRatio) to length of gutter
-	//   - constrain to minimum length of handle
-	// - set handle to constrained length
-	// - apply (value) to length of gutter minus length of handle
-	// - that is the handle position
 }
 
 func (this scrollbarLayout) viewportContentRatio () float64 {
 	if this.linked == nil { return 0 }
-	return this.viewportLength / this.contentLength
+	return this.viewportLength() / this.contentLength()
 }
 
 func (this scrollbarLayout) viewportLength () float64 {