Before a primitive is blended with the framebuffer, it goes through an alpha test stage which lets you discard fragments based on the current alpha value.
This function lets you change the function used to evaluate the alpha channel, and thus determine which fragments are discarded and which continue on to the blending stage.
The default is cogl_pipeline_alpha_func_always
| this |
A Pipeline object |
| alpha_func |
A |
| alpha_reference |
A reference point that the chosen alpha function uses to compare incoming fragments to. |