\class SoAlphaTest SoAlphaTest.h
\brief The SoAlphaTest class is a node used to control the GL alpha test function.
- With this node you can control the OpenGL alpha test function.
+ With this node you can control the OpenGL alpha test function. The
+ alpha test function enables you to discard fragments based on its
+ alpha value. For instance, if you set the function to LESS and value to
+ 0.5, all fragments with alpha value less than 0.5 (or 128 in pixel
+ values) will be discarded.
+ Alpha testing is typically used when rendering textures where all
+ pixels are either completely opaque or completely
+ transparent. Transparency sorting propblems are avoided when alpha
+ testing is used instead of blending, since depth testing can still
+ be enabled and no sorting or delayed rendering is needed.
+ To enable alpha testing instead of transparency blending, insert a
+ TransparencyType node with value = NONE, and an AlphaTest node with
+ function set to LESS and value set to for instance 0.5.