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Periodic functions
mod can be used to construct periodic
functions.
If f(x) is a function defined on [0, p] then f (mod(x,p)) will give a periodic version of f
Spectral Synthesis Noise
What is noise
Random signal with rich frequency
distribution
Types of noise:
White – uniform frequency Pink – filtered Gaussian – based on Gaussian distribution
None appropriate for shader use
Noise
Perlin on noise:
“Noise appears random but it is not. If it were really random,
then you’d get a different result each time you call it. Instead it is “pseudo-random” – it gives the appearance of randomness”
“Noise is a mapping from Rn→ R – you input an n-
dimensional point with real coordinates and it gives you a real value. Currently, the most common uses is for n=1, 2, and 3. The first is used for animation, the second for cheap texture hacks, and the third for less-cheap texture hacks.”
Noise
Repeatable Known range [0, 1]
Note original Perlin noise returns [-1 1]
Band limited / scalable Doesn’t exhibit obvious periodicities Statistically invariant under translation Statistically invariant under rotation
Noise
Noise parameters
noise (float) -- 1D noise noise (float, float) -- 2D noise noise (point) -- 3D noise noise (point, float) -- 4D noise
In Cg
noise[1234] (x) -- x can be (float, vec2,
vec3, vec4).
