"layer.fx_" functions and Layer.fx_onGetPixelR() information

[AndrewMackowski]

I've looked all over, but I haven't found explanations for all the layer.fx_ functions, and especially

code:
extern Double Layer.fx_onGetPixelR(double r, double d, double x, double y);

extern Double Layer.fx_onGetPixelD(double r, double d, double x, double y);

extern Double Layer.fx_onGetPixelX(double r, double d, double x, double y);

extern Double Layer.fx_onGetPixelY(double r, double d, double x, double y);

extern Double Layer.fx_onGetPixelA(double r, double d, double x, double y);

Does anyone know what they do, or tell me where to find this out?