Hi all,

I'm working on something horror-themed, possibly for a portfolio. I have a visual effect which can be applied a certain amount, let's say a floating point number from 0 to 100 for the sake of argument. In keeping with the horror theme I want the effect to progress in a somewhat jerky unpredictable manner with pauses. Any assistance with choosing an appropriate function would be appreciated. Some desired characteristics are below:

• Monotonic
• Some pseudo-random component
• Has pauses (plateaux)
• Has some sense of momentum (e.g. derivative has some pattern, not just spikes)

Some approaches that I considered which don't quite make the grade:

• A random walk with another function as the envelope (no pattern to derivative, timing too predictable)
• Some monotonic function plus noise (timing too predictable, may not be monotonic)

Maybe I'll have to go piecewise, but I hope not.

Any thoughts would be appreciated!

JT

You might want to consider multi-octave noise. What you're describing seems to be a random walk with high and low frequency (pause) components, which can easily be obtained by mixing noise functions from different octaves.

This particular article talks about multi-octave perlin noise in a single dimension:

http://freespace.virgin.net/hugo.elias/models/m_perlin.htm

Thanks all, some options for me to try out. I suspect the tan option won't be right, the parts that tend to infinity would need to be worked around, plus I'm not sure I want that extreme a slope. Alvaro, I suspect that you and frying_pan are talking about similar things. Using perlin noise as the noise function may give nice results.

Just in case you want to go the multi-octave route, I'd suggest looking at simplex noise, which is essentially the same concept but implemented more efficiently (using a dimensionally minimal set of gradients). There are really nice c++ implementations that are plug and play here. The lowest dimension noise you can get with that code is 2D, but you can just ignore one dimension.

If I recall correctly, Perlin noise suffers badly in higher-dimension forms, I think 1D with a few octaves will be fine. ;) Plus I already have the code (somewhere).