The VSL Effect can be used for defining arbitrary pixel effects. Using the VSL shading language, the user can move data from a channel to another one, blend channels together, make color corrections, etc.
The Image Coordinate Channel defines the channel, which the effect uses to identify the coordinates of the processed pixel. The pixel coordinates are in floating point form: the top left corner has the coordinates (0,0,0) and the bottom right corner is (1,1,0). Use of relative floating point coordinates guarantees that VSL effects are resolution independent. When rendering boxes, the pixel coordinates are scaled to the range, which the box covers of the total image. Therefore, you can safely use box rendering with this effect.
The default image coordinate channel is the 'UV coords' channel. In the example image above, a random noise is added to the rendered image. The amount of noise depends on the UV coords.
The lower part of the VSL effect's property window contains the standard VSL editor. By checking the Advanced option, you get access to the editing tools. See the Materials chapter for VSL programming instructions.
The VSL objects of the image processing tree see all channels of the system and can freely perform any suitable computations using the channels. Because of the auto-configuration property of the post processing system, referring a channel from a VSL object automatically includes the channel in the post processing data flow.