OpenGL's Rasterization Rule

Hey guys, I am trying to compare the results of OpenGL and Ray-casting and therefore came across a problem about the rasterization rule. I searched from google and found the similar thing in the MSDN network of Dx10 (so called top-left rule). However, there are hardly any information about OpenGL.

Actually, I would like to know how OpenGL generate the fragment for pixel which positioned inside a triangle or on the edge of a triangle. As a result, my ray-casting would be adjusted according to it.

Thanks first for your help!

http://www.opengl.org/registry/doc/glspec30.20080811.pdf
Chapter 3

Find it! Thank you very much Simon!