volume
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float volume(vector pos, ...)
Note
This function relies on the fact that VEX “knows” that pos has
derivatives (dPdu, dPdv, and dPdz).
Passing a literal vector instead of a special variables such as P
will return 0 since VEX will not be able to access the derivatives.
Derivatives options
derivatives-options
Section titled “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
Section titled “examples”Return the volume of the current micro-voxel in camera space:
volume(P)Returns 0, since the argument is not a variable VEX knows the derivatives for:
volume({0.1, 2.3, 4.5})