Why Is this Code Not Working

Arvin1209

class Points{
  PVector pos;
  PVector vel = new PVector();
  PVector acc = new PVector();
  Points(float x_, float y_){
    pos = new PVector(x_,y_);
  }
  void applyForce(PVector force){
    acc.add(force);
  }
  void update(){
    vel.add(acc);
    pos.add(vel);
    acc.mult(0);
    show();
  }
  void show(){
    strokeWeight(3);
    stroke(255);
    ellipse(pos.x,pos.y,10,10);
  }
}
ArrayList<PVector> charges = new ArrayList<PVector>();
ArrayList<Points> particles = new ArrayList<Points>();


void setup(){
  size(500,500);
  for(int i = 0; i < 2; i++){
    charges.add(new PVector(random(height),random(width),round(random(1))));
  }
  for(int i = 0; i < 100; i++){
    particles.add(new Points(random(height),random(width)));
    print(particles.get(i).pos);
  }
}

PVector efield(PVector pos){
  PVector force = new PVector();
  for(PVector charge:charges){
    PVector poscopy = pos;
    PVector chargecopy = charge;
    float strength = charge.z/pow(dist(pos.x,pos.y,charge.x,charge.y),2); 
    poscopy.sub(chargecopy);
    poscopy.normalize();
    poscopy.mult(strength);
    force.add(poscopy);
  }
  return force;
}

void draw(){
  background(0);
  for(Points p:particles){
    p.applyForce(efield(p.pos));
    p.update();
  }
}

This code is only showing points in one corner of the screen, instead of simulating electric field lines like it should be doing.

Chrisir

Line 30 you swap width and height

Why the 3rd parameter, it’s a 2D sketch?

You only have 2 charges

Arvin1209

The third parameter for the charges is for positive or negative charge

Arvin1209

class Points{
  PVector pos;
  PVector vel = new PVector();
  PVector acc = new PVector();
  Points(float x_, float y_){
    pos = new PVector(x_,y_);
  }
  void applyForce(PVector force){
    acc.add(force);
  }
  void update(){
    vel.add(acc);
    vel.mult(0.9);
    pos.add(vel);
    acc.mult(0);
    if(pos.x > width){
      pos.x = 0;
    }
    if(pos.y > height){
      pos.y = 0;
    }
    if(pos.x < 0){
      pos.x = width;
    }
    if(pos.y < 0){
      pos.y = height;
    }
    show();
  }
  void show(){
    //strokeWeight(3);
    //stroke(255);
    ellipse(pos.x,pos.y,2,2);
  }
}
ArrayList<PVector> charges = new ArrayList<PVector>();
//ArrayList<Points> particles = new ArrayList<Points>();


void setup(){
  fullScreen();
  //for(int i = 0; i < 4; i++){
  //  charges.add(new PVector(random(height),random(width),round(random(-1,1))));
  //}
  //for(int i = 0; i < 1000; i++){
  //  particles.add(new Points(random(height),random(width)));
  //  //print(particles.get(i).pos);
  //}
}

PVector efield(PVector pos){
  PVector force = new PVector();
  for(PVector c:charges){
    PVector poscopy = pos;
    PVector chargecopy = c;
    float strength = c.z*10000/pow(dist(poscopy.x,poscopy.y,chargecopy.x,chargecopy.y),2); 
    poscopy.sub(chargecopy);
    poscopy.normalize();
    poscopy.mult(strength);
    force.add(poscopy);
  }
  //print(force);
  return force;
}

void draw(){
  background(150);
  //for(Points p:particles){
  //  p.update();
    //p.applyForce(efield(p.pos.copy()));
  //  //print(p.pos);
  //}
  for(int x = 0; x < width; x+= 20){
    for(int y = 0; y < width; y+= 20){
      PVector dir = efield(new PVector(x,y));
      stroke(255);
      drawArrow(x,y,dir.mag(),dir.heading());
    }
  }
  for(PVector c:charges){
    if(c.z < 1){
      fill(0);
    }
    if(c.z < 0){
      noFill();
    }
    else{
      fill(255);
    }
    ellipse(c.x,c.y,2,2);
  }
  if(mousePressed && mouseButton == LEFT){
    charges.add(new PVector(mouseX,mouseY,1));
  }
  if(mousePressed && mouseButton == RIGHT){
    charges.add(new PVector(mouseX,mouseY,-1));
  }
}

void drawArrow(float cx, float cy, float len, float angle){
  pushMatrix();
  strokeWeight(1);
  translate(cx, cy);
  rotate(angle);
  line(0,0,len, 0);
  line(len, 0, len-2,-2);
  line(len, 0, len-2,2);
  popMatrix();
}

I changed my code to show arrows instead of points but now only the first point I place has an effect on the code. It should give all charges the same effect based on the distance but it isn't working.

Chrisir

WHy don’t you init charges in setup () anymore?

Arvin1209

I wanted to keep charges empty and have control over where I add them.

Chrisir

mainly, in efield you need to use .copy()

        PVector poscopy = pos.copy();
        PVector chargecopy = c.copy();













class Points {
  PVector pos;
  PVector vel = new PVector();
  PVector acc = new PVector();
  Points(float x_, float y_) {
    pos = new PVector(x_, y_);
  }
  void applyForce(PVector force) {
    acc.add(force);
  }
  void update() {
    vel.add(acc);
    vel.mult(0.9);
    pos.add(vel);
    acc.mult(0);
    if (pos.x > width) {
      pos.x = 0;
    }
    if (pos.y > height) {
      pos.y = 0;
    }
    if (pos.x < 0) {
      pos.x = width;
    }
    if (pos.y < 0) {
      pos.y = height;
    }
    show();
  }
  void show() {
    //strokeWeight(3);
    //stroke(255);
    ellipse(pos.x, pos.y, 2, 2);
  }
}

// ==========================================================


ArrayList<PVector> charges = new ArrayList<PVector>();
//ArrayList<Points> particles = new ArrayList<Points>();


void setup() {
  fullScreen();
  //for(int i = 0; i < 4; i++){
  //  charges.add(new PVector(random(height),random(width),round(random(-1,1))));
  //}
  //for(int i = 0; i < 1000; i++){
  //  particles.add(new Points(random(height),random(width)));
  //  //print(particles.get(i).pos);
  //}
}

PVector efield(PVector pos) {

  PVector force = new PVector();

  for (PVector c : charges) {

    PVector poscopy = pos.copy();
    PVector chargecopy = c.copy();

    float strength = c.z*10000/pow(dist(poscopy.x, poscopy.y, chargecopy.x, chargecopy.y), 2);

    poscopy.sub(chargecopy);
    poscopy.normalize();
    poscopy.mult(strength);
    force.add(poscopy);
  }

  //print(force);
  return force;
}

void draw() {
  background(150);
  //for(Points p:particles){
  //  p.update();
  //p.applyForce(efield(p.pos.copy()));
  //  //print(p.pos);
  //}
  for (int x = 0; x < width; x+= 20) {
    for (int y = 0; y < width; y+= 20) {
      PVector dir = efield(new PVector(x, y));
      stroke(255);
      drawArrow(x, y, dir.mag(), dir.heading());
    }
  }
  for (PVector c : charges) {
    if (c.z < 1) {
      fill(0);
    }
    if (c.z < 0) {
      noFill();
    } else {
      fill(255);
    }

    ellipse(c.x, c.y, 2, 2);
  }//for
}

void mousePressed() {

  if (mousePressed && mouseButton == LEFT) {
    charges.add(new PVector(mouseX, mouseY, 1));
  }
  if (mousePressed && mouseButton == RIGHT) {
    charges.add(new PVector(mouseX, mouseY, -1));
  }
}

void drawArrow(float cx, float cy, 
  float len, 
  float angle) {

  pushMatrix();
  strokeWeight(1);
  translate(cx, cy);
  rotate(angle);
  line(0, 0, len, 0);
  line(len, 0, len-2, -2);
  line(len, 0, len-2, 2);
  popMatrix();
}