DrawGeometry() in OnRender() method

Question

I have a UserControl which overrides the OnRender-Method as follow:

MyUsercontrol.cs:

MyUserControl: UserControl
{
    protected override void OnRender(DrawingContext dc)
    {
       dc.DrawRectangle(Brushes.White, new Pen(Brushes.Black,1), new Rect(0,10,50,30));

       var visualBrush = new VisualBrush(new UserControl1{Height=30, Width=50});           
       dc.DrawGeometry(visualBrush, null, new RectangleGeometry(new Rect(50,10,50,30)));           
    }
}

The UserControl used above looks like this (defined in xaml, without additional codebehind code):

<UserControl x:Class="VisualBrushExample.UserControl1" ...>
<Grid>
   <Border BorderThickness="1" BorderBrush="Black" Background="White" CornerRadius=8,0,0,8"/>
</Grid>
</UserControl>

Now if I use MyUserControl I get following output:

example of created output with MyUserControl

My question now is, if there exists a way how I can use UserControl1 in the OnRender() method without get this transparent border around the UserControl1-Rectangle.

Thanks in advance, rhe1980

What transparent border do you mean? And if this is really about drawing two rectangles on top of each other, it's the most complicated and confusing way to do. — Clemens, Jul 04 '12 at 13:49
the left Usercontrol (with the rounded corners) is smaller then the right one. It seems to me like dc.DrawGeometry() use a Pen even thoug 'null' is passed. — rhe1980, Jul 04 '12 at 13:55
maybe it looks complicate. in fact I only want to place a UserControl into an other during the OnRender() method. And yes, there are other (better) ways to use the UserControl (like in xaml etc.). But Im only modifying an existing UserControl which use this machanism. — rhe1980, Jul 04 '12 at 13:59

score 0 · Accepted Answer · answered Jul 04 '12 at 14:33

The reason that you see differently sized rectangle is simple. When you draw a rectangle with a Pen, the Pen line is centered on the rectangle's edges, or in other words the edge lies in the middle of the line. Therefore half of the Pen width lies outside the rectangle in each direction. Hence you have to add one Pen width to the rectangle's width and height to get the total size of the drawing output, 51 x 31 in your example.

You can perhaps check this by the Geometry.GetRenderBounds method.

DrawGeometry() in OnRender() method

1 Answers1