Dw VEX function

Takes the derivative of the given value with respect to the 3rd axis, for volume rendering.

See also: Du, Dv

1. float Dw(float p)

2. vector Dw(vector p)

3. vector4 Dw(vector4 p)

In shading contexts, this is the change in the variable over the volume being shaded. When rendering surfaces, this function returns 0.

You can specify optional parameters to control the computation.