Transparency in a figure

How I can do to make a shape has a transparent fill?

Hi

If you use the fixed pipeline, you can use the alpha blending, look at GL_BLEND and glBlendFunc. There is an example of the OpenGL red book ported to JOGL 2 available in the project jogl-demos:
https://github.com/sgothel/jogl-demos/blob/master/src/redbook/src/glredbook10/alpha.java