Processing: Creative Coding and Computational Art

x+=xSpeed;
println("x = " + x + " increase = " + (x-x2));
x2 = x;
}
}
The output shows the increase in y is changing while the increase in x remains constant at
3, which causes the curved motion in the example.
In the previous accelerated bouncing rectangle example, the rectangle collided with the
ground and bounced, and then the process repeated itself while the sketch continued running.
In the real world, if we dropped a bouncy box, when the box collided with the
ground, there would be a transfer of some of its bouncing energy (into heat, sound, etc.),
causing the box to eventually come to a rest on the ground. You may remember Newton’s
law of conservation of energy, which states that energy in a closed system remains constant—it
can be transferred but not created or destroyed. So, in technical terms, we could
say that when the rectangle collides with the ground, there is a transfer of its kinetic
energy into thermal (heat) and mechanical (sound) energy. Rather than deal with the real
physics of this type of energy transfer, I’ll simply create a damping variable (a fractional
value) and multiply ySpeed by it each time the rectangle hits the ground.
The damping variable will eventually stop the rectangle’s motion along the y-axis, but I also
need to stop the rectangle’s movement along the x-axis—if I don’t, the rectangle will continue
to slide back and forth along the bottom of the display window. To fix this, I’ll create
a friction variable, which will gradually slow the rectangle’s sideways motion using the
same approach as with the damping variable. Each time the rectangle collides with the bottom
of the display window, xSpeed is multiplied by the friction variable (also a fractional
value). In the real world, friction would also slow the rectangle as it moved through the air
and made contact with the side walls—but we’ll ignore this for now (although you could
easily add in these calculations as well).
// Simple Motion Physics I
float speedX, speedY;
float x, y, w, h;
// acceleration force
float gravity;
Figure 11-7.
Output of Acceleration Calculations sketch
MOTION
495
11