Hi

I am trying to simulate the behaviour of hairs clinging to each other...but I need some advice. I have a first stab but it's not quite working - I think the issue is with the particle system, but I am open to the possibility I am thinking about the whole system all wrong... I appreciate any advice

[quote]
import traer.animation.*;
import traer.physics.*;
ParticleSystem ps;
ArrayList fixed = new ArrayList();//, free;
ArrayList hairs = new ArrayList();

void setup() {
  size(1026,830);
  ps = new ParticleSystem( 0, 0.25 );
  for (int i=0; i<5; i++){
    Particle tempP = ps.makeParticle(1, random(0,width),random(0,height), 0);
    tempP.makeFixed();
    fixed.add(tempP);
  }
  for (int i = 0; i < fixed.size(); i++) {  
    Particle p1 = (Particle)fixed.get(i);
    for (int j = i+1; j < fixed.size(); j++) {  
      Particle p2 = (Particle)fixed.get(j);
      PVector pPosA = new PVector(p1.position().x(), p1.position().y());
      PVector pPosB = new PVector(p2.position().x(), p2.position().y());
      float tempDist = PVector.dist(pPosA, pPosB);
      if(tempDist>400){
        Hair tempStrand = new Hair(ps.getParticle(i), ps.getParticle(j));
        hairs.add(tempStrand);
      }
    }
  }

  for (int i = 0; i < hairs.size(); i++) {  
    Hair h1 = (Hair)hairs.get(i);
    Particle tempA = h1.mid;
    for (int j = i+1; j < hairs.size(); j++) {
      Hair h2 = (Hair)hairs.get(j);
      Particle tempB = h2.mid;
      Attraction tempAtt = ps.makeAttraction(tempA, tempB, 10000,15);
    }
  }
  smooth();
}
void draw() {
  background(0);
  ps.tick();
  if (mousePressed)
  {
    fixedP.moveTo(mouseX, mouseY, 0);
    fixedP.velocity().clear();
  }
  strokeWeight(4);
  stroke(100);
  for (int i = 0; i < fixed.size(); i++) {  
    Particle p = (Particle)fixed.get(i);
    ellipse(p.position().x(),p.position().y(), 10, 10);
  }
  strokeWeight(0.5);
  stroke(100);
  noFill();
  for (int i = 0; i < hairs.size(); i++) {  
    Hair h = (Hair)hairs.get(i);
    h.draw();
  }
}
void mousePressed()
{
  int mx = mouseX;
  int my = mouseY;
  float d = -1.0;
  PVector mousePos = new PVector(mx, my, 0);
  for(int i=0; i<ps.numberOfParticles(); i++) {
    Particle pTemp = ps.getParticle(i);
    PVector particlePos = new PVector(pTemp.position().x(),pTemp.position().y() );    
    float dTemp = PVector.dist(particlePos, mousePos);
    if (dTemp < d || d < 0)
    {
      d = dTemp;
      fixedP = pTemp;
    }
  }
}
void mouseReleased()
{
  if (keyPressed)
  {
    if (key == ' ')
    {
      fixedP.makeFixed();
    }
  }
  else
  {
    fixedP.makeFree();
  }
  fixedP = null;
}

[quote]
class Hair{
  Particle a;
  Particle b;
  Particle mid;
  Hair(Particle a, Particle b){
    this.a = a;
    this.b = b;  
    mid = ps.makeParticle(1, (a.position().x()+b.position().x())/2, (a.position(
).y()+b.position().y())/2, 0);
    Spring tempSpringA = ps.makeSpring(a, mid,1,1,100);
    Spring tempSpringB = ps.makeSpring(b, mid,1,1,100);
  }
  void draw(){
    noFill();
    beginShape();
    stroke(100);
    curveVertex(a.position().x(), a.position().y());
    curveVertex(a.position().x(), a.position().y());
    curveVertex(mid.position().x(),  mid.position().y());
    curveVertex(b.position().x(),  b.position().y());
    curveVertex(b.position().x(),  b.position().y());
    endShape();
    fill(255);
  [quote]
    [color=#

quite right. they're minor things, I just ran out of space i guess.

the last draw function in the class Hair can just be closed. My version had an ellipse drawn at the midpoint of each hair, And there also needs to be a new varable declared at the top of the sketch called fixedP...

Since yesterday I realised that I could maybe add some more particles along each hair's length but that still doesn't address the issue I had which was that the force of attraction that I was using to generate the "cling" was kind of erratic and no sooner had these points been pulled together they had been driven apart again. I guess it might have to do with the momentum of the initial motion...still I wonder if there is a way to manage this behaviour so the two particles come to a settled position close to one another.

//global variable
Particle fixedP;

//to be inserted in the hair class
void draw(){
   noFill();
   beginShape();
   stroke(100);
   curveVertex(a.position().x(), a.position().y());
   curveVertex(a.position().x(), a.position().y());
   curveVertex(mid.position().x(),  mid.position().y());
   curveVertex(b.position().x(),  b.position().y());
   curveVertex(b.position().x(),  b.position().y());
   endShape();
   fill(255);
ellipse(mid.position().x(),  mid.position().y(), 5, 5);
}
}

ok. I'm back at it and struggling really badly. I need help from someone who has a really good grasp on the forces in a physics system, particularly Traer's. What I'm having trouble getting a hold on is getting my particles to 'dampen' and to 'cling' to one another. Right now, they seem to pull together only to be ripped apart again.

My hunch is that I need to develop an elaborate pattern of turning forces on or off depending on distance but I don't really know. I seem to have played around with every conceivable combination of values for attraction and spring values but I can't seem to get a good feel for how to tame these things.

Really, I could use a hand. the sketch can be seen here:
http://www.upsdn.ca/processing/hairExtensions01g_3d/applet/

thanks so much!

thanks so much for the reply!

and sorry bout the browser problem. I just noticed too that it doesnt work for me either on the web...I'l try and sort that out and repost but as for your suggestion about tinkering with the forces I noticed there's an update to the library that allows for new forces to be added. What would this stickiness force look like? Any quick ideas off the top of your head?

and about the default repulsion - I'm not sure about that. What I do know, is that I was referring to particles that do have attraction between them so that they are drawn together....I would assume that the attraction would override the repulsion since it's really just accumulating or summing vectors - and the greater of the two should just cancel the smaller out, no?

thanks again

How big is your example system?  If there are a large number of particles, try reducing to a smaller size and see if that works.

mhuyk

i uploaded a really simple demo of the problem I'm talking about.

http://www.upsdn.ca/processing/hairplay_att_experiment/applet/

MODIFICATION: note that you have to drag the fixed endpoints in such a way that the fixed particles come within a certain proximity of each other in order to see the effect I'm talking about....you can then fix them if you hold the space bar down when you release the mouse click....

note that the particles never really fully settle together but get propelled apart as soon as they come within a certain proximtiy...

thanks for the advice in advance

Thanks for that Jack. I haven't actually considered what the magnitude of those forces are and, moreover, that there may be limits to the size a float can hold.

I have since been in touch with Jeff Traer and he was able to suggest a number of really minor tweaks that instantly made a difference - like the Physics time step, the drag, and the attraction forces all of which I decreased and achieved much better results.

I guess I am not mindful enough of what calculations are actually going on and that you will get drastically different behaviours depending on the proportions between them - I thought I had played around with them plenty but apprently not enough.

thanks again for the advice.