How to make a diagram (texture, material)?


If I have three (or more) variables: R, G, B, which are 0.33, 0.33, 0.34 (for example), and I want to draw a circle, which shows these variables as a diagram. All parts start drawing from upper center point. One part of this circle is red and is 33% of circle area, second is green and is also 33% of circle, third is blue and is 34% of circle area. I haven’t find any related tutorials. What kinds of texture and material I need to do it?

Picture 1. Example.