ianhi_processing/NatureOfCode/The-Nature-of-Code-Examples-master/Processing/chp4_systems/NOC_4_08_ParticleSystemSmoke/NOC_4_08_ParticleSystemSmoke.pde
// The Nature of Code
// Daniel Shiffman
// http://natureofcode.com

// Smoke Particle System

// A basic smoke effect using a particle system
// Each particle is rendered as an alpha masked image

/* @pjs preload="processingjs/chapter04/_4_08_ParticleSystemSmoke/data/texture.png"; */

ParticleSystem ps;

void setup() {
  size(640,360);
  PImage img = loadImage("texture.png");
  ps = new ParticleSystem(0,new PVector(width/2,height-75),img);
}

void draw() {
  background(0);
  
  // Calculate a "wind" force based on mouse horizontal position
  float dx = map(mouseX,0,width,-0.2,0.2);
  PVector wind = new PVector(dx,0);
  ps.applyForce(wind);
  ps.run();
  for (int i = 0; i < 2; i++) {
    ps.addParticle();
  }
  
  // Draw an arrow representing the wind force
  drawVector(wind, new PVector(width/2,50,0),500);

}

// Renders a vector object 'v' as an arrow and a location 'loc'
void drawVector(PVector v, PVector loc, float scayl) {
  pushMatrix();
  float arrowsize = 4;
  // Translate to location to render vector
  translate(loc.x,loc.y);
  stroke(255);
  // 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();
}

