How to preserve distance between 3d objects in order that they won't collide?!

lolonulu

Hi, I was wondering if someone could check this method based on shiffman's nature of code's one. In my sketch some spheres rotate in a 3d space and I try to force them to stay at a certain distance that they won't collide and stick together... Here is just the method below...Thanks a lot in advance ;))

void separate (Sphere[]planets) {
    float desiredDist = radius*6;
    PVector sum = new PVector();
    int count = 0;
    if (planets != null) {
      if (level > 0 ) {
        for (int i = 0; i <planets.length; i++) {
          int j=1;
          for (j+=i; j<planets.length; j++) {
            float d = PVector.dist(planets[i].location, planets[j].location);
            if ((d >0) && (d<desiredDist)) {
              PVector diff = PVector.sub(planets[i].location, planets[j].location);
              diff.normalize();
              diff.div(d);
              sum.add(diff);
              count++;
            }

            if (count > 0) {
              sum.div((float)count);
            }
            if (sum.mag() > 0) {
              sum.setMag(maxSpeed);
              PVector steer = PVector.sub(sum, velocity);
              steer.limit(maxForce);
              applyForce(steer);
            }
          }
        }
      }
    }
  }

jeremydouglass

@lolonulu -- is your goal to create a 3D sphere effect like the Bouncing Bubbles example for ellipses -- collision detection that affects direction and speed?

• https://processing.org/examples/bouncybubbles.html

lolonulu

Dera Jeremy, thank you for your answer, yes this is my goal, but with 3d spheres...

kfrajer

Notice line 11 d>0, d is always positive. In this line, you are excluding the case d==0 which probly you don't want to... In other words, this checking is redundant and not needed.

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For lines 8 and 9 should become:

for (int j=i+1; j<planets.length; j++) {

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Line 13 and 14 are doing the same thing, so you are normalizing twice. You need only one of them so keep the first line.

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There is something that I don't understand with on your code and it is regarding the count variable. The count variable never gets reset. I don't think this is a desirable design in your case.

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Vector velocity showed up in your code with no warning. How is this vector related to the current planet as pointed out by the index i?

Also, I think line 10 should read:

float d = PVector.dist(planets[j].location, planets[i].location); //Indices switched!

I suggest you do the debugging of your core code in a simple sketch, maybe a universe confined in a square box and study the bouncy of spheres in this space.

Kf

koogs

Also, I think line 10 should read: ... // Indices switched!

Surely the distance between a and b is the same as the distance between b and a. It's commutative - order doesn't matter.

koogs

Runable examples are always better.

jeremydouglass

I agree with koogs -- add a very short runnable example showing how you are using separate in a simple sketch.

lolonulu

Thank you very much Kfrajer, koogs and Jeremy, yes I will try with a short runnable example to debugg my code, then I'll post it. Tomorrow I think...Thank you guys for your replies

kfrajer

You are right @koogs, The dist() function returns a scalar and I was thinking in vectorial space. The distance is only required to check for the closeness between any two spheres. @lolonulu is taking care of the vectorial calculation in line 12.

You can always explore code available online: https://www.google.ca/search?q=java+collision+3D&rlz=1C1CHWA_enCA688CA688&oq=java+collision+3D&aqs=chrome..69i57j0l5.3502j0j8&sourceid=chrome&ie=UTF-8#q=processing+collision+3D

Kf

lolonulu

Dear kfrjer, koogs and jeremydouglas,

I think I found the solution in a code available online: https://www.openprocessing.org/sketch/397053 Here is the part of the method that I used to calculate the distance detween the 3d spheres:

          for(Particle p1: particles){ // declare two lists of particles
            for(Particle p2: particles){
              if(p1 == p2){continue;} // if the same go on
              float d = PVector.dist(p1.loc, p2.loc); // calculate the dist between locations
              if(d <= p1.radius + p2.radius){
                PVector p12 = PVector.sub(p2.loc, p1.loc);// sub. loc. 1 from loc.2
                PVector n = PVector.div(p12, p12.mag()); // divide this vector by its magnitude
                PVector v12 = PVector.sub(p2.vel, p1.vel); // now do the same for velocity: substract p1 velocity from P2 velocity
                PVector vn1 = PVector.mult(n, PVector.dot(p1.vel, n)); // multiply n(p12 div. by its own magnitude) by the dot product of vel.p1 by n!
                PVector vt1 = PVector.sub(p1.vel, vn1); // substract the result from velocity of p1
                PVector t = PVector.div(vt1, vt1.mag()); // divide this vector by its magnitude
                float spring = -k * (p1.radius + p2.radius - d); // we pass a negative value (-2=-k) in order to multiply the distance/spring
                float j = (1 + e) * (p1.mass * p2.mass / (p1.mass + p2.mass)) * PVector.dot(v12, n); 
                // e and mass=1, so here it's 2 multiply by the dot product of the vectors V12 and n
                PVector impulse = PVector.mult(n, j + spring); // this last vector impulse
                equals to n multiply by j+spring
                p1.nvel.add(impulse); // finally we add this vector impulse to our new velocity (: nvel) in order the speheres will repulse each other
              }
            }
          }

      for(Particle p: particles){
        p.updateVel();
      }

    /////////////////////////////////////////////////////////////////////////

    void updateVel(){
        vel = nvel;
        nvel = new PVector(vel.x, vel.y, vel.z);

      }

I hope it will be helpful to anyone. The best is to check out the original sketch off course! Thanks a lot guys for your help. I appreciate ;) best, l