// jkriss ~ 4 april 2004

Point points[] = new Point[50];
int count = 0;
float mx, my;
float oldMouseX, oldMouseY;
float w,h;

float r = 0;
float g = 127;
float b = 255;
float arr,gee,bee;
float ri = 3;
float gi = 4;
float bi = 5;

void setup() {
  size(500,300);
  smooth();
  framerate(30);
  w = width/2;
  h = height/2;
}

void loop() {
  drawStuff();
}

color setAlpha(color c, float a) {
  arr = red(c);
  gee = green(c);
  bee = blue(c);
  return color(arr,gee,bee,a);
}

void updateColor() {
  if (r > 255 || r < 0) ri=-ri;
  if (g > 255 || g < 0) gi=-gi;
  if (b > 255 || b < 0) bi=-bi;
  
  r += ri;
  g += gi;
  b += bi;
}

void drawStuff() {

  background(255);

  mx = mouseX;
  my = mouseY;
  
  if (count >= 20) count = 0;

  for (int i=0; i<21; i++) {
    if (points[i+1] != null) points[i] = points[i+1];
  }
  
  points[20] = new Point(mx, my, 0, (mx - oldMouseX)/2 + random(1.0) -1, (my - oldMouseY)/2 + random(1.0) - 1, random(4), random(6)+2, color(r,g,b));
  updateColor();
  count++;
 
  oldMouseX =  mx;
  oldMouseY = my;

  Point p = null;
  noStroke();
  
  beginShape(TRIANGLE_STRIP);
  color mainColor;
      
  for (int i=0; i<21; i++) {
    if (points[i] != null ) {
    
      p = points[i]; 
      mainColor = setAlpha(p.pcolor, abs(i*p.vx*1.5));
      stroke(mainColor);
      fill(mainColor);
      vertex(p.x,p.y);
      vertex(p.x+p.s,p.y+p.s);
      p.x += p.vx;
      p.y += p.vy;
      p.vx *= 1.06;
      p.vy *= 1.06;
    }
  }
  endShape();
}

class Point {
  float x,y,z;
  float vx,vy,vz;
  float s; //size of line
  color pcolor;
  Point (float x, float y, float z, float vx, float vy, float vz, float s, color pcolor) {
    this.x = x;
    this.y = y;
    this.vx = vx;
    this.vy = vy;
    this.z = z;
    this.vz = vz;
    this.s = s;
    this.pcolor = pcolor;
  }
}