[Visualpython-users] Pixel-oriented plotting

[Bruce S. <Bru...@nc...>]

A colleague asked me about pixel-oriented plotting in VPython, for doing 
such things as chaos-related plots. I replied that there really isn't 
good support for that in the production version of VPython, though the 
new "points" object in the beta version is appropriate.

But then I realized that there is something one can do: Create a stack 
of horizontal lines (curve objects) and set colors at points that way. 
It works, and in the contributed section of vpython.org there is now a 
little program pixelplot.py which makes a display of the famous 
Mandelbrot set. The program also checks to see whether there is a 
"points" object available and uses that, which is faster and simpler.

There's a slightly tricky issue when using curves, which is explained in 
the documentation for curve. Colors are interpolated between points. So 
to make the right color at a point, you have to stick in an extra point. 
So 4 pixels requires 8 points on the curve: 0-1, 1-2, 2-3, 3-4.

Bruce Sherwood

P.S. In the process I found that there are bugs in the points object. It 
dies when you try to append more than 33000 points. Dunno why yet. But 
this doesn't affect the posted program.