Dynamically controlled particle system with Toxiclibs

narner

Hi all,

I'm working on modifying the Attraction2D example from the Toxiclibs library to be controlled by gestures from a Leap Motion sensor, as opposed to the mouse in the example.

I'm doing all my gesture recognition in an Open Frameworks app, and sending that over OSC.

When a "Gesture 0" event occurs, I call the method below to remove the gestureAttractor from the physics object:

void resetAttraction() {
  if (gestureAttractor != null){
      physics.removeBehavior(gestureAttractor);
      println("ATTRACTOR NULL");
     } else {
        println("not null");
     }
}

If a "Gesture 1" event occurs, I call this method to create a new gestureAttractor, and add it back to the physics object:

void addAttraction(){ if (gestureAttractor == null) { println("ATTRACTOR NULL"); position1.set(340, 191); gestureAttractor = new AttractionBehavior2D(position1, 250, 0.9f); physics.addBehavior(gestureAttractor); } else { println("not null"); } }

What seems to happen consistently is whenever the gesture state changes, I'll get a "Concurrent Modification Exception" crash at physics.update(); in the draw method.

I'm sure it has something to do with the way the lifecycle of these objects are handled, but I haven't been able to determine anything yet - anyone have any ideas?

Below is the entirety of the sketch:

import toxi.geom.*;
import toxi.physics2d.*;
import toxi.physics2d.behaviors.*;

import oscP5.*;
import netP5.*;

OscP5 oscP5;

int NUM_PARTICLES = 750;

VerletPhysics2D physics;
//AttractionBehavior2D mouseAttractor;
AttractionBehavior2D gestureAttractor;


//Vec2D mousePos;
Vec2D position1;


boolean isGestureAttractorAdded;

void setup() {
  size(680, 382,P3D);
  // setup physics with 10% drag
  physics = new VerletPhysics2D();
  physics.setDrag(0.05f);
  physics.setWorldBounds(new Rect(0, 0, width, height));
  // the NEW way to add gravity to the simulation, using behaviors
  physics.addBehavior(new GravityBehavior2D(new Vec2D(0, 0.15f)));

  // start oscP5, listening for incoming messages at port 12000 
  oscP5 = new OscP5(this, 6000);

  position1 = new Vec2D(340, 191);

  addAttraction();

  //gestureAttractor = new AttractionBehavior2D(position1, 250, 0.9f);
  //physics.addBehavior(gestureAttractor);
}

void addParticle() {
  VerletParticle2D p = new VerletParticle2D(Vec2D.randomVector().scale(5).addSelf(width / 2, 0));
  physics.addParticle(p);
  // add a negative attraction force field around the new particle
  physics.addBehavior(new AttractionBehavior2D(p, 20, -1.2f, 0.01f));
}

void draw() {
  background(255,0,0);
  noStroke();
  fill(255);
  if (physics.particles.size() < NUM_PARTICLES) {
    addParticle();
  }
  physics.update();
  for (VerletParticle2D p : physics.particles) {
    ellipse(p.x, p.y, 5, 5);
  }
}

void mousePressed() {
  //position1 = new Vec2D(mouseX, mouseY);
   //create a new positive attraction force field around the mouse position (radius=250px)
  //gestureAttractor = new AttractionBehavior2D(position1, 250, 0.9f);
  //physics.addBehavior(gestureAttractor);

  //println(physics.behaviors);
}

void mouseDragged() {
  // update mouse attraction focal point
  //position1.set(mouseX, mouseY);
}

void mouseReleased() {
  // remove the mouse attraction when button has been released
  //physics.removeBehavior(gestureAttractor);
}


///// OSC RECEIVING

void oscEvent(OscMessage theOscMessage) {
  /* check if theOscMessage has the address pattern we are looking for. */

  if (theOscMessage.checkAddrPattern("/gesture_classification") == true)  {
    /* check if the typetag is the right one. */
    if(theOscMessage.checkTypetag("i")) {
      /* parse theOscMessage and extract the values from the osc message arguments. */
      int gestureClassLabel = theOscMessage.get(0).intValue();  
      println(" Gesture is: ", gestureClassLabel);

      if (gestureClassLabel == 0){   
        resetAttraction();
      } else if (gestureClassLabel == 1) {       
        addAttraction();
      } else if (gestureClassLabel == 2) {
          //physics.removeBehavior(gestureAttractor);
      } 
    }  
  } 

}

//////METHODS FOR SETTING POSITION / REMOVAL OF ATTRACTORS...

void resetAttraction() {
  if (gestureAttractor != null){
      physics.removeBehavior(gestureAttractor);
      println("ATTRACTOR NULL");
     } else {
        println("not null");
     }
 }

void addAttraction(){
     if (gestureAttractor == null) {
         println("ATTRACTOR NULL");
         position1.set(340, 191);
         gestureAttractor = new AttractionBehavior2D(position1, 250, 0.9f);
         physics.addBehavior(gestureAttractor);
     } else {
       println("not null");
     }
}

narner

I figured out a workaround - by adding in code to print the error exception, the crash didn't occur anymore:

      try
  {
      physics.update();

  }
   catch (Exception e)
  {
    e.printStackTrace();
  }

For reference, the result of printing the stacktrace is:

at java.util.TimerThread.mainLoop(Timer.java:555) at java.util.TimerThread.run(Timer.java:505)

jeremydouglass

@GoToLoop, any advice on handling concurrent modification in this scenario?

Past related discussions:

• https://forum.processing.org/two/search?Search=concurrent

narner

@jeremydouglass: @GoToLoop's answers in this thread to answer my question:

https://forum.processing.org/two/discussion/comment/90265/#Comment_90265

I added protected volatile to my potentially unthread safe variables - that seems to do the trick, but I'm of course open to any other thoughts!

narner

I think I was wrong - that really didn't do much when pushing the sketch further (i.e., adding more particles).

@GoToLoop, any thoughts at all?

GoToLoop

Like I've just advised on this recent forum thread below:
https://forum.Processing.org/two/discussion/23063/how-to-run-a-segment-of-code-uninterrupted#Item_2

You should transfer VerletPhysics2D::particles container so it is handled by 1 Thread only.

Rather than calling functions resetAttraction() & addAttraction(), which mutates the VerletPhysics2D::particles btW, from within oscEvent(), which runs outside the "Animation" Thread, make gestureClassLabel global, and just set it within oscEvent().

Within draw(), check gestureClassLabel within a switch () / case: block, calling the corresponding function according to the gestureClassLabel's current value.

Don't forget to always reset it back to some value which represents no action, like -1 or something like that, right after the switch () / case: block. :P

narner

Hey @GoToLoop, thank you for this - that helps a lot.

I tried your suggestion, and seem to have resolved the concurrency errors I was experiencing.

However, what seems to be happening now is that

So, here's what the sketch looks like before I added your changes in, but with the concurrency errors (every time a new gesture occurs, the particles move).

Here's what happens when I add your changes in - no concurrency errors, but it seems that the sketch is only processing the change from a single gesture...after one occurs, any additional gestures have no effect.

As you suggested, I made gestureClassLabel a global variable: int gestureClassLabel;

And inside my OSC message method, I set the value of that variable accordingly.

Inside my drawmethod, I've added the switch/case statement as so:

void draw() {
  background(255,0,0);
  noStroke();
  fill(255);
  if (physics.particles.size() < NUM_PARTICLES) {
    addParticle();
  }

  physics.update();

  switch(gestureClassLabel) {
    case 0: {
      println("GESTURE 0");
      addGestureZeroAttraction();
    }

    case 1: {
      println("GESTURE 1");
      addGestureOneAttraction();
    }

    case 2: {
      println("GESTURE 2");
      resetAttraction();
    }
  }

  gestureClassLabel = -1;

  for (VerletParticle2D p : physics.particles) {
    ellipse(p.x, p.y, 5, 5);
  }

}

GoToLoop

You've forgotten about keyword break to isolate each case:! #-o
https://Processing.org/reference/switch.html

Obviously the last case: doesn't need it. But most folks like the redundant break there too. :))

P.S.: Curly {} brackets are also unnecessary for case:'s statements. ;;)

narner

@GoToLoop Oh...well that was dumb of me :(

So, I made the change you suggested here, but the same behavior still occurs...wonder if I'm going to have to rethink how I'm approaching all of this...

    void draw() {
      background(255,0,0);
      noStroke();
      fill(255);
      if (physics.particles.size() < NUM_PARTICLES) {
        addParticle();
      }

      physics.update();  

      switch(gestureClassLabel) {
        case 0: 
          println("GESTURE 0");
          addGestureZeroAttraction();
          break;

        case 1: 
          println("GESTURE 1");
          addGestureOneAttraction();
          break;

        case 2: 
          println("GESTURE 2");
          resetAttraction();
          break;
      }

      gestureClassLabel = -1;

      for (VerletParticle2D p : physics.particles) {
        ellipse(p.x, p.y, 5, 5);
     }
}

GoToLoop

• There's some fault in 1 of my advises: Unconditionally assigning -1 to gestureClassLabel. b-(
• Function draw() is called back at about 60 FPS.
• So it's impressively easy to reset the value received from oscEvent() back to -1 before it had a chance to be processed later within draw(), given each function is concurrently executed by their own threads! #-o
• Well, here's my proposed fix this time... 8-|

if (gestureClassLabel >= 0) {
  switch (gestureClassLabel) {
    // ... all your case: conditions below:
  }

  gestureClassLabel = -1;
}

narner

@GoToLoop Also makes sense! Still the same :/ Wonder if adjusting the sketch's framerate will help...

narner

So, it seems that swapping out switch/case for an if/else block seems to be doing the trick...

physics.update();

  if (gestureClassLabel == 0) {
      println("GESTURE 0");
      addGestureZeroAttraction();
      gestureClassLabel = -1;
  } else if (gestureClassLabel == 1) {
      println("GESTURE 1");
      addGestureOneAttraction();
      gestureClassLabel = -1;
  } else if (gestureClassLabel == 2) {
      println("GESTURE 2");
      resetAttraction();
      gestureClassLabel = -1;
  }

GoToLoop

• Glad you've finally made it. Congrats! <:-P
• But I'm puzzled why a chain of else if {} would work while switch () { case: } wouldn't! :-/
• Then I've decided to refactor the whole code. #:-S
• Given I can't have any inputs from OSC, I can only use mouse for such task here. 8-|
• Maybe it will for ya this time if you run the refactored sketch I hope. O:-)

/**
 * Attraction2D + OSC (v1.2.3)
 * Copyright © 2010 Karsten Schmidt
 * Mods Narner & GoToLoop (2017-Jun-14)
 *
 * GNU.org/licenses/lgpl-2.1.html
 *
 * forum.Processing.org/two/discussion/22940/
 * dynamically-controlled-particle-system-with-toxiclibs#Item_12
 */

import toxi.geom.Vec2D;
import toxi.geom.Rect;

import toxi.physics2d.VerletPhysics2D;
import toxi.physics2d.VerletParticle2D;

import toxi.physics2d.behaviors.ConstantForceBehavior2D;
import toxi.physics2d.behaviors.AttractionBehavior2D;

import oscP5.OscP5;
import oscP5.OscMessage;

static final boolean MOUSE = true;
static final float STRENGTH = .9, DRAGGING = .05, GRAVITY = .15;
static final int PARTICLES = 600, DIAM = 5, AREA = 250;
static final int SMOOTH = 2, FPS = 60, PORT = 6000;

int oscGesture = -1;
color bg = #008000;

final VerletPhysics2D physics = new VerletPhysics2D();

final AttractionBehavior2D attractor =
  new AttractionBehavior2D(new Vec2D(), AREA, 0);

final StringBuilder sb = new StringBuilder(30);

void setup() {
  size(680, 382, FX2D);
  smooth(SMOOTH);
  frameRate(FPS);

  colorMode(RGB);
  blendMode(REPLACE);

  stroke(-1);
  strokeWeight(DIAM);

  physics.particles.ensureCapacity(PARTICLES);
  ((ArrayList<?>) physics.behaviors).ensureCapacity(PARTICLES + 2);

  physics.setWorldBounds(new Rect(0, 0, width, height)).setDrag(DRAGGING);
  physics.addBehavior(new ConstantForceBehavior2D(new Vec2D(0, GRAVITY)));
  physics.addBehavior(attractor);

  new OscP5(this, PORT);
  registerMethod("pre", this);
}

void pre() {
  Vec2D v = Vec2D.randomVector().scaleSelf(DIAM).addSelf(width>>1, DIAM<<2);
  VerletParticle2D p = new VerletParticle2D(v);

  physics.addParticle(p)
    .addBehavior(new AttractionBehavior2D(p, DIAM<<2, -1.2, .01));

  if (physics.particles.size() == PARTICLES)  unregisterMethod("pre", this);
}

void draw() {
  processChosenGesture(oscGesture);
  //processChosenGesture((int) random(20));

  background(bg);
  for (final Vec2D p : physics.update().particles)  point(p.x, p.y);

  displayInfoTitle()
}

void mousePressed() {
  if (MOUSE) {
    attractor.getAttractor().set(mouseX, mouseY);
    attractor.setStrength(STRENGTH);
    bg = #800000;
  }
}

void mouseDragged() {
  if (MOUSE)  attractor.getAttractor().set(mouseX, mouseY);
}

void mouseReleased() {
  if (MOUSE)  disableGestureAttraction();
}

void oscEvent(final OscMessage msg) {
  oscGesture = msg.get(0).intValue();
  println("Received gesture was:", oscGesture);
}

void displayInfoTitle() {
  sb.setLength(0);

  sb.append("Particles: ").append(physics.particles.size())
    .append("  -  FPS: ").append(round(frameRate));

  getSurface().setTitle(sb.toString());
}

void processChosenGesture(final int gesture) {
  if (gesture < 0)  return;

  oscGesture = -1;
  println("Gesture to process is:", gesture);

  switch (gesture) {
  case 0:
    activateGestureAttraction(); 
    break;
  case 1:
    setRandomPositionForAttractor(); 
    break;
  case 2:
    disableGestureAttraction();
  }
}

void activateGestureAttraction() {
  attractor.getAttractor().set(width>>1, height>>1);
  attractor.setStrength(STRENGTH);
  bg = #FF0000;
}

void setRandomPositionForAttractor() {
  attractor.getAttractor()
    .set(random(DIAM, width - DIAM), random(DIAM, height - DIAM));
}

void disableGestureAttraction() {
  attractor.setStrength(0);
  bg = #0000FF;
}

narner

That worked amazingly @GoToLoop...thank you so much for the help!!!