   making a pie chart
  I want to make a pie chart that changes as the relative values change. More specifically, I want to take a circular image I have and overlay the colors on it. The only way I can think of to do this is basically create a Line class then draw it 360 times with increasing angles on top of the image with a lower opacity and change the colors accordingly.Is there a better way to do this?   
  I'd suggest drawing triangles and not lines, since you'll have to change the number of lines if you change the size, in order to make them cover the circle.You could create a vertex buffer containing the centre point of the circle and the list of points on the circumference, and an index buffer. Then for each slice of the pie draw the relevant range of the index buffer. The colour could be set as a shader constant or the texture factor (depending on how you draw).   