The Henon fractal above is calculated using an equation with the supplied parameter "a". Vary it by moving the slider and you vary the results. Click the recalculate button to cause it to redraw. You may need to do this to get the image started the first time.

The algorithm steps through all the points along a diagonal line from the center to one of the corners of the rectangle shown. Starting with each of these points the equation is iterated and at every iteration the resulting value is marked on the rectangle with a coloured pixel. All the pixels belonging to a given starting point use the same colour. After a few hundred iterations [or when the value goes out of the rectangle] the algorithm steps on to the next starting point and a new colour.

[Caution: calculation and drawing may also occur when you are off page]