Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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Figure 7-10. Falling random bouncing strands
This example is similar to the last, but I achieved the curved motion using a slightly different
algorithm. Instead of multiplying y by a ratio, I used a double arithmetic incrementation.
The lines
ySpeed[i] += accel[i];
y[i] += ySpeed[i];
create the acceleration. It may not be immediately apparent how this works. However, if
you look at a few values during the loop iterations, it becomes clear what’s happening. To
keep things simple, let’s assume the value assigned to accel, for one of the particles, is .1.
Following are the ySpeed and y values after five iterations:
iteration1: ySpeed= .1, y = .1
iteration2: ySpeed = .2, y = .3 (y change: .2)
iteration3: ySpeed = .3, y = .6 (y change: .3)
iteration4: ySpeed = .4, y = 1.0 (y change: .4)
iteration4: ySpeed = .5, y = 1.5 (y change: .5)
Notice how the y value is changing by an increasing interval: .2, .3, .4, .5; this is what generates
the acceleration.
The display window collision detection allows the particles to remain active longer and
thus graphically add to the image. The detection is pretty straightforward: if a particle’s y
position is greater than or equal to the height of the display window, then reverse the
direction of the particle and also multiply ySpeed by the gravity variable. Here’s the code
snippet:
// check ground detection only
if ( y[i]>=height){
// reverse particle direction
ySpeed[i]*=-1;