add property tree verbiage
They show up in the Property Tree under sim/rendering/als-secondary-lights and can be activated or manipulated by normal [[Nasal|Nasal]] calls or [[Xml|XML]].
=== Effects File ===
The effects file is the mechanism we use to combine and manipulate all the necessary data to create stunning visual effects. It's the link between the data contained and produced in [[Nasal|Nasal]], [[Xml|XML]] and the Property Tree and the graphics rendering pipeline. It's there to allow us to create these affects without having to know or use the C++ code base. Its flexible framework allows for an almost infinite range of sophisticated effects.
==== Parameters ====
Parameter entries defined in the Effect file correspond to a
property tree data container (static or variable). They will contain the data needed by the shader program to perform its magic. The type of information contained in the property tree might be program control data or variable/static data that the shader program can manipulate prior to sending on to render.
In the case of ALS Lights, below is some of the data passed to, and used by, the shader program.
Note the "use-searchlight" entry, it is pointing to the use-searchlight entry in the
property tree under "sim/rendering/als-secondary-lights" that was defined in preferences.xml.
Some of this data may play a duel role inside the shader program. In other words it might be used to control other functions in addition to ALS Lights.
Note how "use_searchlight" is used in the main function to determine if the property defined in preferences.xml and manipulated in the
property tree is set to true or 1.
Some of the variable data contained in the shader program is used for other purposes and is introduced into the shader program from other property, parameter and uniform definitions not pertaining to ALS Lights.