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 how to do this?

here’s a nice Blend Utility

Here’s the Final result – thanks to BlueMonkMN

 Rectangle GetSquareRec(double radius, int x, int y)     {         double r = radius;         double side = Math.Sqrt(Math.Pow(r, 2) / 2);         Rectangle rec = new Rectangle(x - ((int)side), y - ((int)side), (int)(side * 2) + x, (int)(side * 2) + y);          return rec;     }     void Form1_Paint(object sender, PaintEventArgs e)     {           Graphics gTarget = e.Graphics;         gTarget.SmoothingMode = SmoothingMode.AntiAlias;           GraphicsPath pTemp = new GraphicsPath();          Rectangle r = GetSquareRec(200, 225, 225);         pTemp.AddEllipse(r);         pTemp.AddEllipse(GetSquareRec(50, 225, 225));          Color[] colors = new Color[5];         colors[0] = Color.FromArgb(192, 192, 192);         colors[1] = Color.FromArgb(105, 0, 0);         colors[2] = Color.FromArgb(169, 169, 169);         colors[3] = Color.FromArgb(0, 0, 0);         colors[4] = Color.FromArgb(0, 0, 0);          float[] positions = new float[5];         positions[0] = 0f;         positions[1] = 0.1f;         positions[2] = 0.35f;         positions[3] = 0.5f;         positions[4] = 1f;          ColorBlend Cb = new ColorBlend();         Cb.Colors = colors;         Cb.Positions = positions;          PathGradientBrush pgb = new PathGradientBrush(pTemp);         pgb.InterpolationColors = Cb;         pgb.CenterPoint = new PointF(r.X + (r.Width / 2), r.Y + (r.Height / 2));         gTarget.FillPath(pgb, pTemp);      } 

http://www.freeimagehosting.net/uploads/th.515733e62e.jpg

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;