public sealed override void CustomDrawToThisCanvas(Canvas canvas, Rectangle updateArea)
{
canvas.OffsetCanvasOrigin(-myviewportX, -myviewportY);
updateArea.Offset(myviewportX, myviewportY);
this.DrawBoxContent(canvas, updateArea);
canvas.OffsetCanvasOrigin(myviewportX, myviewportY);
updateArea.Offset(-myviewportX, -myviewportY);
}