How do I draw an annulus (doughnut) using GDI+?

Question

I have been trying to draw an annulus (ring with thickness) with a transparent hole and a gradient rim in C# with very little success. Does anyone have any suggestions on ho

Answer 1

This is how I did it in the Scrolling Game Development Kit:

pTemp = new GraphicsPath();
pTemp.AddEllipse(Start.X, Start.Y, End.X - Start.X, End.Y - Start.Y);
pTemp.AddEllipse((Start.X * 3 + End.X) / 4f,
                 (Start.Y * 3 + End.Y) / 4f,
                 (End.X - Start.X) / 2f,
                 (End.Y - Start.Y) / 2f);
PathGradientBrush pgb = new PathGradientBrush(pTemp);
Blend b = new Blend();
b.Factors = new float[] { 0, 1, 1 };
b.Positions = new float[] { 0, .5F, 1 };
pgb.Blend = b;
pgb.CenterColor = ((SolidBrush)CurrentBrush).Color;
pgb.SurroundColors = new Color[] {CurrentPen.Color};
gTarget.FillPath(pgb, pTemp);
pgb.Dispose();
pTemp.Dispose();

_{(source: enigmadream.com)}

I edited the original SGDK code for this sample because originally I wasn't smart enough to scale the gradient to exclude the hole, but now I guess I am :).

If you would rather see the gradient like this:

_{(source: enigmadream.com)}

Then change the blend code to look like this:

Blend blend = new Blend();
blend.Factors = new float[] { 0, 1, 0, 0 };
blend.Positions = new float[] { 0, 0.25F, .5F, 1 };
pgb.Blend = blend;

Answer 2

You may use two calls to Graphics.DrawArc combined, drawing the top and bottom or left and right portions of the annulus, one portion at a time.