9.5.2

886 • CHAPTER 18
THE SHADERS • 887
Type
This is the distortion algorithm to be used.
Directional
The value of the distortion channel is added to the sample coordinate of the texture.
Bidirectional
The value of the distortion channel is added to the sample coordinate of the texture if the value is
between 50-100% and is subtracted if the value is between 0-50%.
Flow Field
The distortion value is determined by evaluating the ow direction of the distortion texture and then
the ow direction vector is used to offset the sample coordinate of the texture.
Wrap
The Wrap function controls what happens to parts of the texture that have been distorted and now
lie outside the UV map. These can be ignored (None), repeated (Cycle), cut off (Clamp) or mirrored
(Seamless).
Amount
Global distortion amount. 100% means distortion values from 0 to 1 in UV and 0 to 10 in 3D.
X, Y, Z
X is the distortion amount in U for 2D and X for 3D. Y is the distortion amount in V for 2D and Y for
3D. Z is the distortion amount in Z for 3D.
Delta
Delta is a scaling factor to use in sampling the texture for evaluating slope to be used in the bump
channel. This allows you to get very sharp bump with minute detail that is not possible with the
standard bump delta.
Step
Relative step size to be used in evaluating the ow direction in Flow Field distortion type.