Collision with a circular container

Programming Questions

awdriggs

Collision with a circular container

in Programming Questions • 1 year ago

I've struggling to figure out to problems with a sketch.

1) right now when a small circle hits the outer "container" which is another circle, it will bounce if, which is what I want. But i'm only changing the velocity, which means that they circle bounces right back off and heads in the same directions. I would like to do something more "realistic" and have it bounce of at an angle, but I'm struggling with the match behind this.

2) Sometimes when the small circles collide, they stick together. this especially happens when you click in the same space that a circle is moving through. Each click adds a new circle. How do I get them not to stick together?

I know there are better physics engines for collisions, but I want this to be able to run in javascript using processing.js

If anyone has ideas for improvement would really love to here them!

here is the entire code.

ArrayList colliz = new ArrayList();
boolean showVectors = true;
int xOrigin, yOrigin, diameter, cRadius;
PVector center;
void setup() {
size(500, 500);
smooth();
xOrigin = width/2;
yOrigin = height/2;
diameter = width-100;
cRadius = diameter/2;
center = new PVector(xOrigin, yOrigin);
for (int i = 0; i < 1; i++) {
colliz.add(new Circ(new PVector(random(5), random(-5, 5)), new PVector(width/2, height/2)));
}
}
void draw() {
background(100);
noFill();
stroke(255);
ellipse(250, 250, diameter, diameter);
for (int i = 0; i < colliz.size(); i++) {
Circ test = (Circ) colliz.get(i);
test.go();
for (int j = 0; j < colliz.size(); j++) {
Circ collide = (Circ) colliz.get(j);
test.collideEqualMass(collide);
}
}
}
void mousePressed() {
//showVectors = !showVectors;
colliz.add(new Circ(new PVector(random(5), random(-5, 5)), new PVector(mouseX, mouseY)));
}
class Circ {
PVector loc;
PVector vel;
float bounce = 1.0;
float r = 5;
boolean colliding = false;
boolean isIn = true;
PVector ploc;
Circ(PVector v, PVector l) {
vel = v.get();
loc = l.get();
}
// Main method to operate object
void go() {
update();
borders();
render();
}
// Method to update location
void update() {
ploc = loc;
vel.limit(5);
loc.add(vel);
}
void borders() {
// TEST TO SEE IF A CIRCLE CAN BE USED AS THE BOUNDRY
//
if (loc.dist(center) >= cRadius) {
float a = PVector.angleBetween(loc, center);
ploc.sub(vel);
vel.y *= -bounce;
vel.x *= -bounce;
//loc.x = ploc.x*.99;
//loc.y = ploc.y*.99;
//loc.limit(diameter);
loc.x = ploc.x;
loc.y = ploc.y;
}
//inside();
// if (isIn == false){
// vel.y *= -bounce;
// vel.x *= -bounce;
//
// loc.x = ploc.x;
// loc.y = ploc.y;
// }
// THIS IS FOR USING THE SCREEN AS BOUNDRY
// if (loc.y > height) {
// vel.y *= -bounce;
// loc.y = height;
// }
// else if (loc.y < 0) {
// vel.y *= -bounce;
// loc.y = 0;
// }
// if (loc.x > width) {
// vel.x *= -bounce;
// loc.x = width;
// }
// else if (loc.x < 0) {
// vel.x *= -bounce;
// loc.x = 0;
// }
}
void inside() {
if ((sq(loc.x - xOrigin) + sq(loc.y - yOrigin)) <= sq(cRadius)) {
isIn = true;
}
else {
isIn = false;
}
}
// Method to display
void render() {
ellipseMode(CENTER);
noStroke();
fill(255);
ellipse(loc.x, loc.y, r*2, r*2);
if (showVectors) {
drawVector(vel, loc, 10);
}
}
void collideEqualMass(Circ t) {
float d = PVector.dist(loc, t.loc);
float sumR = r + t.r;
// Are they colliding?
if (!colliding && d <= (sumR+1) ) {
// Yes, make new velocities!
colliding = true;
// Direction of one object another
PVector n = PVector.sub(t.loc, loc);
n.normalize();
// Difference of velocities so that we think of one object as stationary
PVector u = PVector.sub(vel, t.vel);
// Separate out components -- one in direction of normal
PVector un = componentVector(u, n);
// Other component
u.sub(un);
// These are the new velocities plus the velocity of the object we consider as stastionary
vel = PVector.add(u, t.vel);
t.vel = PVector.add(un, t.vel);
}
else if (d > sumR) {
colliding = false;
}
}
}
PVector componentVector (PVector vector, PVector directionVector) {
//--! ARGUMENTS: vector, directionVector (2D vectors)
//--! RETURNS: the component vector of vector in the direction directionVector
//-- normalize directionVector
directionVector.normalize();
directionVector.mult(vector.dot(directionVector));
return directionVector;
}
void drawVector(PVector v, PVector loc, float scayl) {
pushMatrix();
float arrowsize = 4;
// Translate to location to render vector
translate(loc.x,loc.y);
stroke(0);
// Call vector heading function to get direction (note that pointing up is a heading of 0) and rotate
rotate(v.heading2D());
// Calculate length of vector & scale it to be bigger or smaller if necessary
float len = v.mag()*scayl;
// Draw three lines to make an arrow (draw pointing up since we've rotate to the proper direction)
line(0,0,len,0);
line(len,0,len-arrowsize,+arrowsize/2);
line(len,0,len-arrowsize,-arrowsize/2);
popMatrix();
}
//void mousePressed() {
// showVectors = !showVectors;
//}

Replies(3)

PhiLho

Re: Collision with a circular container

1 year ago

Have you seen the Standard Examples > Topics > Motion > BouncyBubbles sketch? It has exactly the behavior (not simple) that you try to implement.

If you prefer to do it yourself, see http://en.wikipedia.org/wiki/Elastic_collision article.

About circles remaining stuck, you might test the click position with regard to existing circles: if too close of one of them, try a randomly chosen place near the click position (or reject the click).

allonestr..

Re: Collision with a circular container

1 year ago

If the ring is stationary, then you may treat the collision of the ball and the ring as the collision between the ball and a straight line - the straight line being the tangent to the ring at the point of collision.

Just as with light, the angle of incidence equals the angle of reflection.

For the maths, there are two ways of dealing with this:

• when the ball hits the ring, find the angle between its motion and the tangent (remember that the tangent is at 90degrees to the radius), and then work out the reflected motion. One way of doing this is to rotate the collision so that you're bouncing off a vertical or horizontal line (as you already know how to do this), and then rotate the results back.

See "Foundation ActionScript Animation Making Things Move" by Keith Peters for an excellent explanation of this.

• use vector maths as I did in this sketch http://www.openprocessing.org/sketch/40818. I too struggled with getting the reflection right until I twigged that the ball was bouncing off the tangent to the ring.

I found these two websites very useful for the vector maths:

               
                  http://sebleedelisle.com/2010/01/predicting-circle-line-collisions/

               
                  http://www.tonypa.pri.ee/vectors/tut11.html

awdriggs

Re: Collision with a circular container

1 year ago

Thanks allonestring,

Just a quick question, when determining the angle between the ring and the ball, would it world to use the PVector function, angleBetween() instead of atan2()?

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