int pnum = 40;
float gKmin = 0.9;
float gKmax = 0.995;
float gV = 0.5;
float gTrnd = 5;

particleClass[] pList = new particleClass[pnum];
AdditiveCanvasClass aCanvas = new AdditiveCanvasClass();

void setup(){
  size(640,360);
  background(0);
  noStroke();
  fill(0,0,0,0.5);
  
  for(int i=0; i<pnum; i++){
    pList[i] = new particleClass();
    pList[i]._lifeCnt = i*2;
  }
}

void loop(){
  for(int i=0; i<pnum; i++){
    pList[i].step();
    pList[i].step();
  }
}

void keyPressed(){ 
  println(key);
  switch(key){
  case 49:
    background(0);
    gTrnd = 5;
    gV = 0.5;
    gKmin = 0.9;
    gKmax = 0.995;
    break;
  case 50:
    background(0);
    gTrnd = 20;
    gV = 4;
    gKmin = 0.995;
    gKmax = 0.999;
    break;
  case 51:
   background(0,0,0);
    gTrnd = 30;
    gV = 0;
    gKmin = 1;
    gKmax = 1;
    break;
  case 52:
    background(0,0,0);
    gTrnd = 5;
    gV = 0;
    gKmin = 1.5;
    gKmax = 1.2;
    break;
  case 53:
    background(0,0,0);
    gTrnd = 5;
    gV = 5;
    gKmin = 0.9;
    gKmax = 0.95;
    break;
  case 99:
    background(0);
    break;
  }
} 


class particleClass{
  int _lifeCnt;
  float _tx, _ty;
  float _ax, _ay;
  float _vx, _vy;
  float _k;
  float _x, _y;
  color _col,_col2;
  
  particleClass(){
    init();
  }
  
  void init(){
    _x =mouseX;
    _y = mouseY;
    _vx = random(-gV,gV);
    _vy = random(-gV,gV);
    _tx = mouseX + random(-gTrnd,+gTrnd) + random(-gTrnd,+gTrnd) + random(-gTrnd,+gTrnd);
    _ty = mouseY + random(-gTrnd,+gTrnd) +  random(-gTrnd,+gTrnd) +  random(-gTrnd,+gTrnd);
    _ax = 0;
    _ay = 0;
    _k = random(gKmin,gKmax);
    _lifeCnt = 40;
    
    float rr = random(25,40);
    float gg = random(2,rr);
    float bb = random(rr,gg);
    _col = color(rr,gg,bb);
    _col2 = color(rr/3,gg/3,bb/3);
  }
  
  void step(){;
    float dx = _tx - _x;
    float dy = _ty - _y;
    float dist = sqrt(dx*dx+dy*dy);
    if(dist<1){
      dist = 1;
    }
    _vx = _vx * _k + dx/dist * 0.1;
    _vy = _vy * _k + dy/dist * 0.1;
    _x += _vx;
    _y += _vy;
    
    view();
    
    _lifeCnt -= 1;
    if(_lifeCnt<0){
      init();
    }
  }
  
  void view(){
    if(_x > 1 && _x < width-1 && _y > 1 && _y < height-1){
      aCanvas.addColor( int(_x-1), int(_y-1) , _col2);
      aCanvas.addColor( int(_x  ), int(_y-1) , _col2);
      aCanvas.addColor( int(_x+1), int(_y-1) , _col2);
      aCanvas.addColor( int(_x-1), int(_y) , _col2);
      aCanvas.addColor( int(_x),   int(_y) , _col);
      aCanvas.addColor( int(_x+1), int(_y) , _col2);
      aCanvas.addColor( int(_x-1), int(_y+1) , _col2);
      aCanvas.addColor( int(_x  ), int(_y+1) , _col2);
      aCanvas.addColor( int(_x+1), int(_y+1) , _col2);
    }
  }
}




//
//指定したピクセルに色を加算する
class AdditiveCanvasClass{
  AdditiveCanvasClass(){
  }
  
  void addColor(int x, int y, color col){
     int pos;  //position
     float colR, colG, colB;
     color canvCol; //  canvasColor
     color c;
     float canvR, canvG, canvB;   //canvas color Red, Green, Blue

     pos = y * width + x;
     canvCol = pixels[pos];
     canvR = canvCol >> 16  &0xff;
     canvG = canvCol >> 8   &0xff;
     canvB = canvCol        &0xff;
     colR = col >> 16  &0xff;
     colB = col >> 8   &0xff;
     colG = col        &0xff;
     c = color(canvR+colR, canvG+colG, canvB+colB);
     pixels[pos]= c;
  }
}