Progress on scrollbar

scrollbar.go

@@ -65,7 +65,11 @@ func (this *Scrollbar) Link (box tomo.ContentBox) event.Cookie {
 }
 
 func (this *Scrollbar) handleLinkedContentBoundsChange () {
-	// TODO
+	if this.layout.linked == 0 { return }
+	this.layout.value =
+		this.layout.contentPos() /
+		(this.layout.contentLength() - this.layout.viewportLength())
+	this.SetLayout(this.layout)
 }
 
 // SetValue sets the value of the scrollbar between 0 and 1, where 0 is scrolled
@@ -79,13 +83,13 @@ func (this *Scrollbar) SetValue (value float64) {
 // all the way to the left/top, and 1 is scrolled all the way to the
 // right/bottom.
 func (this *Scrollbar) Value () float64 {
-	// TODO
-	return 0
+	if this.layout.linked == nil { return 0 }
+	return this.layout.value
 }
 
 // OnValueChange specifies a function to be called when the position of the
 // scrollbar changes.
-func (this *Slider) OnValueChange (callback func ()) event.Cookie {
+func (this *Scrollbar) OnValueChange (callback func ()) event.Cookie {
 	return this.on.valueChange.Connect(callback)
 }
 
@@ -216,6 +220,7 @@ func (this *scrollbarCookie) Close () {
 
 type scrollbarLayout struct {
 	vertical bool
+	value    float64
 	linked   tomo.ContentBox
 }
 
@@ -229,13 +234,40 @@ func (this scrollbarLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 	handle := image.Rectangle { Max: boxes[0].MinimumSize() }
 	gutter := hints.Bounds
 
+
 	// TODO
-	// - get length of viewport as a percent of length of content
-	// - apply percent to length of gutter
+	// - apply (viewportContentRatio) to length of gutter
 	//   - constrain to minimum length of handle
-	// - set handle to length
-	// - get scroll of content as a percent
-	//   - content pos relative to (content length minus viewport length)
-	// - apply percent to length of gutter minus length of handler
+	// - 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
+}
+
+func (this scrollbarLayout) viewportLength () float64 {
+	if this.vertical {
+		return float64(this.linked.InnerBounds().Dy())
+	} else {
+		return float64(this.linked.InnerBounds().Dx())
+	}
+}
+
+func (this scrollbarLayout) contentLength () float64 {
+	if this.vertical {
+		return float64(this.linked.ContentBounds().Dy())
+	} else {
+		return float64(this.linked.ContentBounds().Dx())
+	}
+}
+
+func (this scrollbarLayout) contentPos () float64 {
+	if this.vertical {
+		return float64(this.linked.ContentBounds().Min.Y)
+	} else {
+		return float64(this.linked.ContentBounds().Min.X)
+	}
+}