Processing: Creative Coding and Computational Art

Asteroid shower in three stages
Now we’ll apply these expressions to our non-orthogonal collision problem, for which
we’ll slowly develop an asteroid shower animation. In my kinder, gentler version, asteroids
pummeling Earth don’t cause cataclysmic destruction, but harmlessly bounce off the
planet’s surface.
In the first stage of the asteroid shower animation, I’ll create a single orb that bounces off
a non-orthogonal surface.
Stage 1: Single orb
The sketch will be developed using six tabs, including the main sketch tab. Three of the
tabs you’ll create will hold classes and the other two will hold functions. The first new tab
I’ll create is for a Ground class. Create a new tab and name it Ground. Enter the following
code into the tab:
class Ground {
float x1, y1, x2, y2;
float x, y, len, rot;
// default constructor
Ground(){
}
// constructor
Ground(float x1, float y1, float x2, float y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
x = (x1+x2)/2;
y = (y1+y2)/2;
len = dist(x1, y1, x2, y2);
rot = atan2((y2-y1), (x2-x1));
}
}
This is a relatively simple class. Objects of the class are instantiated using four arguments,
specifying the left and right coordinates of the top surface of the ground plane. In addition,
within the constructor, a center point (x, y) of the surface is calculated, as is the
ground surface length and the angle of rotation of the surface. Notice how I found the
angle of rotation using the following expression:
rot = atan2((y2-y1), (x2-x1));
You looked at the atan2() function earlier in the chapter. Remember that you can use the
standard trig functions sin(), cos(), and tan() to translate a rotation in the polar coordinate
system to a specific coordinate value in the Cartesian system; and you can use the
MOTION
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