gradient

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vector  gradient(float val, ...)

vector  gradient(vector P, float val, ...)

This method computes the derivative of a volume field using the partial derivatives with respect to a given position (Du, Dv, and Dw). If no position is provided, P is assumed in shading contexts. If only Du and Dv are defined, the derivative will be tangent to the surface being rendered. Derivatives options

derivatives-options

Functions which compute derivatives take additional arguments to allow tuning of the derivative computation.

“extrapolate”, int =0

Whether derivatives are “smooth” across patch boundaries. In most cases this is true and if extrapolation is turned on, derivative computation should be exact for C2 surfaces. However, when the VEX variables are changing with a high frequency (for example, a high frequency displacement map causing high frequency changes to the P variable), extrapolation of derivative computation may cause exaggeration of discontinuities between patch boundaries.

“smooth”, int =1

Adjust the magnitude of the differentials non-uniformly over patches. This will usually reduce patch discontinuities in displacement/textured shaders. However, in some odd cases you may want to turn this feature off.

N = computenormal(P, "extrapolate", 1, "smooth", 0);

Examples

examples

Return the gradient of the density field:

surface test_grad(float density = 0)
{
Cf = gradient(density);
}