From K-3D

Global Variables

The following table lists the set of global variables that can be used by imager shaders:

Name	Type	Storage	Description
Ci	color	varying	Output pixel color (output)
Oi	color	varying	Output pixel opacity (output)
P	point	varying	Pixel raster position
Ci	color	varying	Pixel color
Oi	color	varying	Pixel opacity
alpha	float	uniform	Fractional pixel coverage
ncomps	float	uniform	Number of color components
time	float	uniform	Shutter open time.
dtime	float	uniform	The amount of time the shutter was open.

Geometry of Shading

An imager shader manipulates a final pixel color after all of the geometric and shading processing has concluded. In the context of an imager shader, P is the position of the pixel center in raster space, with the z component being 0. Imager shaders change the value of Ci and Oi.