Add support for scrolling flow layouts to ContainerBox impl

redundantly

box.go

@@ -117,14 +117,34 @@ func (this *box) SetColor (c color.Color) {
 }
 
 func (this *box) SetTexture (texture canvas.Texture) {
+	if this.texture == texture { return }
 	this.texture = xcanvas.AssertTexture(texture)
 	this.invalidateDraw()
 }
 
-func (this *box) SetBorder (border ...tomo.Border) {
-	this.border = border
-	this.invalidateLayout()
-	this.invalidateMinimum()
+func (this *box) SetBorder (borders ...tomo.Border) {
+	previousBorderSum := this.borderSum()
+	previousBorders   := this.border
+	this.border = borders
+
+	// only invalidate the layout if the border is sized differently
+	if this.borderSum() != previousBorderSum {
+		this.invalidateLayout()
+		this.invalidateMinimum()
+		return
+	}
+
+	// if the border takes up the same amount of space, only invalidate the
+	// drawing if it looks different
+	for index, newBorder := range this.border {
+		different :=
+			index >= len(previousBorders) ||
+			newBorder != previousBorders[index]
+		if different {
+			this.invalidateDraw()
+			return
+		}
+	}
 }
 
 func (this *box) SetMinimumSize (size image.Point) {
@@ -285,7 +305,7 @@ func (this *box) Draw (can canvas.Canvas) {
 	if this.transparent() && this.parent != nil {
 		this.parent.drawBackgroundPart(can)
 	}
-	pen.Rectangle(can.Bounds())
+	pen.Rectangle(this.Bounds())
 }
 
 func (this *box) drawBorders (can canvas.Canvas) {
@@ -356,7 +376,11 @@ func (this *box) doMinimumSize () {
 	}
 }
 
+// var drawcnt int
 func (this *box) doDraw () {
+	// println("DRAW", drawcnt)
+	// drawcnt ++
+	
 	if this.canvas == nil { return }
 	if this.drawer != nil {
 		this.drawBorders(this.canvas)
@@ -364,7 +388,11 @@ func (this *box) doDraw () {
 	}
 }
 
+// var laycnt int
 func (this *box) doLayout () {
+	// println("LAYOUT", laycnt)
+	// laycnt ++
+	
 	this.innerClippingBounds = this.borderSum().Apply(this.bounds)
 	if this.parent == nil { this.canvas = nil; return  }
 	parentCanvas := this.parent.canvas()

containerbox.go

@@ -31,11 +31,13 @@ func (backend *Backend) NewContainerBox() tomo.ContainerBox {
 }
 
 func (this *containerBox) SetColor (c color.Color) {
+	if this.color == c { return }
 	this.box.SetColor(c)
 	this.invalidateTransparentChildren()
 }
 
 func (this *containerBox) SetTexture (texture canvas.Texture) {
+	if this.texture == texture { return }
 	this.box.SetTexture(texture)
 	this.invalidateTransparentChildren()
 }
@@ -225,12 +227,6 @@ func (this *containerBox) notifyMinimumSizeChange (child anyBox) {
 	}
 }
 
-func (this *containerBox) boundedLayoutHints () tomo.LayoutHints {
-	hints := this.layoutHints()
-	hints.Bounds = this.ContentBounds().Add(this.InnerBounds().Min)
-	return hints
-}
-
 func (this *containerBox) layoutHints () tomo.LayoutHints {
 	return tomo.LayoutHints {
 		OverflowX: this.hOverflow,
@@ -245,7 +241,7 @@ func (this *containerBox) contentMinimum () image.Point {
 	minimum := this.box.contentMinimum()
 	if this.layout != nil {
 		layoutMinimum := this.layout.MinimumSize (
-			this.boundedLayoutHints(),
+			this.layoutHints(),
 			this.children)
 		if this.hOverflow { layoutMinimum.X = 0 }
 		if this.vOverflow { layoutMinimum.Y = 0 }
@@ -258,8 +254,8 @@ func (this *containerBox) doLayout () {
 	this.box.doLayout()
 	previousContentBounds := this.contentBounds
 
-	// by default, use innerBounds for contentBounds. if a direction
-	// overflows, use the layout's minimum size for it.
+	// by default, use innerBounds (translated to 0, 0) for contentBounds.
+	// if a direction overflows, use the layout's minimum size for it.
 	var minimum image.Point
 	if this.layout != nil {
 		minimum = this.layout.MinimumSize (
@@ -267,19 +263,33 @@ func (this *containerBox) doLayout () {
 			this.children)
 	}
 	innerBounds := this.InnerBounds()
-	this.contentBounds = innerBounds
+	this.contentBounds = innerBounds.Sub(innerBounds.Min)
 	if this.hOverflow { this.contentBounds.Max.X = this.contentBounds.Min.X + minimum.X }
 	if this.vOverflow { this.contentBounds.Max.Y = this.contentBounds.Min.Y + minimum.Y }
-
-	// offset the content bounds by the scroll so children can be positioned
-	// accordingly.
-	this.constrainScroll()
-	this.contentBounds = this.contentBounds.Add(this.scroll).Sub(innerBounds.Min)
 	
 	// arrange children
 	if this.layout != nil {
-		this.layout.Arrange(this.boundedLayoutHints(), this.children)
+		layoutHints := this.layoutHints()
+		layoutHints.Bounds = this.contentBounds
+		this.layout.Arrange(layoutHints, this.children)
 	}
+
+	// build an accurate contentBounds by unioning the bounds of all child
+	// boxes
+	this.contentBounds = image.Rectangle { }
+	for _, box := range this.children {
+		bounds := box.Bounds()
+		this.contentBounds = this.contentBounds.Union(bounds)
+	}
+
+	// constrain the scroll
+	this.constrainScroll()
+
+	// offset children and contentBounds by scroll
+	for _, box := range this.children {
+		box.SetBounds(box.Bounds().Add(this.scroll).Add(innerBounds.Min))
+	}
+	this.contentBounds = this.contentBounds.Add(this.scroll)
 	
 	if previousContentBounds != this.contentBounds {
 		this.on.contentBoundsChange.Broadcast()