Don't invalidate ContainerBox's children when something is set

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()
 }