array position & atan2() in Bouncing Bubbles example in tutorial
in
Programming Questions
•
2 years ago
There are two things I can't understand in the example used in the topic section
( http://processing.org/learning/topics/bouncybubbles.html), see code at the bottom, for quick reference:
davide
CODE:
( http://processing.org/learning/topics/bouncybubbles.html), see code at the bottom, for quick reference:
- The collide Method starts with a for() whose argument starts with i=id+1 (where id is the position in the array of the bubbles). Now, I see that the code works, but I don't see how: if the considered bubble is, for example, the fourth, how is calculated her behaviour towards the previous ones in the array?
- After, in the same Method there's an atan2() function to get an angle that seems to be calculated using the supposed collision point of the ball with another (dx = others[i].x - x ). The reference says that atan2() calculates the angle "from a specified point to the coordinate origin", so why then this angle serves to calculate the targetX, targetY? Isn't the relative angle between the bubbles to be calculated instead?
davide
CODE:
- int numBalls = 12;
float spring = 0.05;
float gravity = 0.03;
float friction = -0.9;
Ball[] balls = new Ball[numBalls];
void setup()
{
size(640, 200);
noStroke();
smooth();
for (int i = 0; i < numBalls; i++) {
balls[i] = new Ball(random(width), random(height), random(20, 40), i, balls);
}
}
void draw()
{
background(0);
for (int i = 0; i < numBalls; i++) {
balls[i].collide();
balls[i].move();
balls[i].display();
}
}
class Ball {
float x, y;
float diameter;
float vx = 0;
float vy = 0;
int id;
Ball[] others;
Ball(float xin, float yin, float din, int idin, Ball[] oin) {
x = xin;
y = yin;
diameter = din;
id = idin;
others = oin;
}
void collide() {
for (int i = id + 1; i < numBalls; i++) {
float dx = others[i].x - x;
float dy = others[i].y - y;
float distance = sqrt(dx*dx + dy*dy);
float minDist = others[i].diameter/2 + diameter/2;
if (distance < minDist) {
float angle = atan2(dy, dx);
float targetX = x + cos(angle) * minDist;
float targetY = y + sin(angle) * minDist;
float ax = (targetX - others[i].x) * spring;
float ay = (targetY - others[i].y) * spring;
vx -= ax;
vy -= ay;
others[i].vx += ax;
others[i].vy += ay;
println("targetX è "+targetX+"x è "+x);
}
}
}
void move() {
vy += gravity;
x += vx;
y += vy;
if (x + diameter/2 > width) {
x = width - diameter/2;
vx *= friction;
}
else if (x - diameter/2 < 0) {
x = diameter/2;
vx *= friction;
}
if (y + diameter/2 > height) {
y = height - diameter/2;
vy *= friction;
}
else if (y - diameter/2 < 0) {
y = diameter/2;
vy *= friction;
}
}
void display() {
fill(255, 204);
ellipse(x, y, diameter, diameter);
}
}
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