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Randomness in NodeBox OpenGL

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zahar othman

26 Jun, 2014 08:59 AM

Convert few codes from NodeBox 1 examples in Mac to NodeBox OpenGL for my students as most of them use Windows version.

What I notice is that whenever a random command is issued inside the draw method.

say for example: strokewidth(random(1,5))
or any command using random

In Window when the canvas.run(draw) is issued , what being displayed is a blinking screen where the random values keep on changing. This will make random function ineffective inside the draw method. Is it a bug of the run loop?

1. 1 Posted by Stuart Axon on 16 Nov, 2015 10:28 AM

   

   Hopefully this late reply will be useful to someone else...

   If you want to keep the same random value every time you draw a frame, calculate it outside the draw loop, then reuse the same value.

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2. Support Staff 2 Posted by Frederik De Ble... on 15 Dec, 2015 01:17 PM

   

   Randomness in software is tricky. Since the code is executed every frame, and random returns a different value every time it is called, the result will be different for every frame.

   There are two solutions to this:

   1. Pre-calculate the values: that is, they should be random at initialization time (every time the program runs), not for every frame.
      
   2. Use a random seed. Use from random import seed at the top, then in your draw loop, set the seed to a fixed value, like seed(42). Random numbers are not really random, but depend on this seed to generate a series of random values. The same seed always calculates the same series. So by "locking" the seed to a fixed value in the draw call, we can make sure that the values will not change per-frame.
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