c# wpf polygon to bitmap not displaying anything

Question

Sorry if you think this question was already answered, I did look everywhere trying to find out how come when I do this, it is not displaying anything. This is all my code:

Polygon hexagon = new Polygon();
PointCollection pc = new PointCollection();
double side = 25;
double xOffset = 0, yOffset = 0;
double r = System.Math.Cos((System.Math.PI / 180) * 30) * side;
double h = System.Math.Sin((System.Math.PI / 180) * 30) * side;

//Create the 6 points needed to create a hexagon
pc.Add(new Point(xOffset, yOffset)); //Point 1
pc.Add(new Point(xOffset + side, yOffset)); //Point 2
pc.Add(new Point(xOffset + side + h, yOffset + r)); //Point 3
pc.Add(new Point(xOffset + side, yOffset + 2 * r)); //Point 4
pc.Add(new Point(xOffset, yOffset + 2 * r)); //Point 5
pc.Add(new Point(xOffset - h, yOffset + r)); //Point 6

hexagon.Stroke = Brushes.Blue;
hexagon.StrokeThickness = 1;
hexagon.Fill = Brushes.LightBlue;
hexagon.Points = pc;

RenderTargetBitmap bmp = new RenderTargetBitmap(200, 200, 96, 96, PixelFormats.Default);
bmp.Render(hexagon);
img.Source = bmp;

I created a hexagon as a polygon object and I used RenderTargetBitmap to try to convert the polygon to a bitmap but it does not seem to be displaying anything that I can see. I have also added a canvas and added the Polygon object there and that seems to work. It is just when converting to a bitmap. I really am at a lost as to what is wrong in my code. I have everything right now in the main windows loaded event.

Help would be appreciated, thanks.

The solution may be simple or something I overlooked, hopefully the solution is simple :).

Answer 1

A WPF UIElement has to be laid out before being visible. It has to get at least one Measure and Arrange call, where it gets an available Size and a final arrange Rect (usually from its parent Panel). When rendering a newly created element into a RenderTargetBitmap, you would call these methods manually, with appropriate values for the Size and Rect:

...
hexagon.Measure(new Size(200, 200)); // adjust this to your needs
hexagon.Arrange(new Rect(0, 0, 200, 200)); // adjust this to your needs

var bmp = new RenderTargetBitmap(200, 200, 96, 96, PixelFormats.Default);
bmp.Render(hexagon);