How to fill a triangle with gradient using three colors? (maybe using GD)

What is the best way to fill a triangle with gradient, which is formed using three triange vertices. (for example, {RED, BLUE, GREE开发者_StackOverflow社区N}) Implementation language is ruby. Maybe there're some gems or you know such implementation in GD or GD2 library.

You can use RMagick. It's a ruby interface for imagemagick

Try using the sparse_color function