/**
  a spark generator by <a href="http://www.local-guru.net/blog">guru</a>
  
  press 'g' to toggle gravity
*/

import java.util.ArrayList;
import java.util.List;
List particles;
boolean g;

void setup() {
  size(600,300,P2D);
  particles = new ArrayList();
}

void draw() {
  background(0);
  fill(255);
  for( int i =0; i < particles.size(); i++) {
    Particle p = (Particle)particles.get(i);
    if (!p.isDead()) {
      p.update();
      p.draw();
    }
  }
}

void mouseDragged() {
   if (mousePressed ==true ) {
    particles.add( new Particle( new PVector( mouseX, mouseY ), new PVector(random(-1,1),random(-1,1)), 30, g));
   }
}

void keyPressed() {
  if (key == 'g') {
    g = !g;
  }
}

public class Particle {

  PVector p;
  PVector s;
  int ttl;
  boolean g;
  PImage img;
  
  public Particle( PVector p, PVector s, int ttl, boolean g) {
    this.p = p;
    this.s = s;
    this.g = g;
    this.ttl = ttl;
    
    img = makeTexture(5);
  }

  public void update() {
    if ( ttl > 0 ) {
      ttl--;
      p.add( s );
      if ( g ) {
        s = new PVector( s.x, s.y + .1 );
      }
    }
  }
 
  public void draw() {
    if ( !isDead()) {
      blend( img, 0,0, img.width, img.height, int(p.x - img.width/2), int(p.y - img.height/2), img.width, img.height, ADD );
    }
  }
  
  public boolean isDead() {
    return ttl <= 0;
  }
  
  
  PGraphics makeTexture( int r ) {
  PGraphics res = createGraphics( r * 6, r * 6, P2D);
  res.beginDraw();
  res.loadPixels();
    for ( int x = 0; x < res.width; x++) {   
      for( int y = 0; y < res.height; y++ ) {
        float d = min( 512, 50*  sq( r / sqrt( sq( x - 3 * r) + sq( y - 3 * r))));
        //if ( d < 10 ) d = 0;
        res.pixels[y * res.width + x] = color( min(255,d), min(255, d*0.8), d* 0.5 );
      }
    }
  res.updatePixels();
  res.endDraw();
  
  return res;  
}
  
}