light VEX context

Define a light shader with a program called from surface or fog shaders to calculate the illumination of a surface.

Light shaders are called from surface or fog shaders to compute the illumination from a given light source. The light shader can be invoked in an illuminance loop or using the standard diffuse(), specular(), etc. functions.

Globals

Time (read-only)	The time at which the shading occurs, as a number from 0 (shutter open) to 1 (shutter close).
dPdz (read-only)	Floating point step size for volume rendering.
P (read-only)	Position of the point on the surface being shaded. In light or shadow shaders, the P variable contains the point on the light source.
Lz (read-only)	Z-axis in the space of the light. This is a unit vector.
Ng (read-only)	Geometric normal for the surface. This normal represents the “true” normal of the surface being shaded. For example, with Phong shading, the N variable represents the interpolated normal, while the Ng variable represents the true polygon normal.
L	Vector from the point on the surface to the light source. The length of this vector represents the distance to the light source.
dPds (read-only)	Change in position with respect to the parametric s.
I (read-only)	Direction from the eye to the point being shaded. This may or may not be a normalized vector.
Eye (read-only)	Position of the eye.
dPdt (read-only)	Change in position with respect to the parametric t.
t (read-only)	Parametric t (sometimes called v) coordinate of the surface being shaded.
N (read-only)	Shading normal for the surface.
Cl	Light color.
s (read-only)	Parametric s (sometimes called u) coordinate of the surface being shaded.
Ps (read-only)	Position of the point on the surface being illuminated.