// catherine wheel - By Nick - coolbubble.com - 5.11.04

color colBackground;
float friction = 0.96f;
float gravity = 0.2f;
float startSpeed = 1.5f;
int maxLife = 50;//100;
int numParticles=2000;//5000;
int lastFreeParticleIndex=0;
particle[] particles = new particle[numParticles];
float mouseScaler=0.3f;
float mox=mouseX,moy=mouseY;

float wheelSpeed = 0;
float wheelAngle = 0;
float wheelPosX=200;
float wheelPosY=200;
float wheelRadius = 50;

void setup()
{
  size(400,400);
  for (int i=0;i<numParticles;i++)
  {
    particles[i] = new particle();
  }

  framerate(30);
}

void loop()
{
  background(0);

  for (int i=0;i<numParticles;i++)
  {
    if (particles[i].life>0)
    {
      particles[i].process();
    }
  }

  // Add new particles.
  /*
  float mdx=(mouseX-mox)*mouseScaler;
  float mdy=(mouseY-moy)*mouseScaler;
  mox=mouseX;
  moy=mouseY;
  for (int i=0;i<8;i++)
  {
    if (lastFreeParticleIndex>numParticles-1)
    lastFreeParticleIndex=0;

    if (particles[lastFreeParticleIndex].life==0)
    {
      particles[lastFreeParticleIndex].life=maxLife;
      particles[lastFreeParticleIndex].x = mouseX;
      particles[lastFreeParticleIndex].y = mouseY;
      particles[lastFreeParticleIndex].vx = mdx;
      particles[lastFreeParticleIndex].vy = mdy;
      particles[lastFreeParticleIndex].addRandomVelocity();
      particles[lastFreeParticleIndex].r = 255.0f-(random(1.0f)*10.0f);
      particles[lastFreeParticleIndex].g = 255.0f-(random(1.0f)*40.0f);
      particles[lastFreeParticleIndex].b = 160.0f-(random(1.0f)*20.0f);
    }

    lastFreeParticleIndex++;
  }
  */

  // Process wheel.

  float forceFraction=0.01f;
  float spinForce = 0.15f;
  wheelSpeed = (wheelSpeed*(1.0-forceFraction))+(spinForce*(forceFraction));
  wheelAngle += wheelSpeed;
  if (mousePressed) wheelSpeed=0;
  // We need to calculate four directions, but they are all perpendicular so we can get away with one calculation
  float dx = sin(wheelAngle);
  float dy = cos(wheelAngle);
  float vx = -dy;
  float vy = dx;

  // Compute colours.
  float mouseCol = ((float)mouseX/400.0) * 255.0;
  float mouseSat = ((float)mouseY/400.0) * 255.0;
  colorMode(HSB, 255);
  color c = color(mouseCol, mouseSat, 255);
  float r = red(c);
  float g = green(c);
  float b = blue(c);
  mouseCol-=128;
  if (mouseCol<0) mouseCol+=255;
   color c2 = color(mouseCol, mouseSat, 255);
  float r2 = red(c2);
  float g2 = green(c2);
  float b2 = blue(c2);
  colorMode(RGB, 255);

  // Add particles
  addParticles(5, wheelPosX+(wheelRadius*dx),  wheelPosY+(wheelRadius*dy), vx*8.0, vy*8.0, r,g,b);
  addParticles(5, wheelPosX+(wheelRadius*-dx),  wheelPosY+(wheelRadius*-dy), -vx*8.0, -vy*8.0, r2,g2,b2);

}

void addParticles(int num, float x, float y, float dx, float dy, float r, float g, float b)
{
  for (int i=0;i<8;i++)
  {
    if (lastFreeParticleIndex>numParticles-1)
    lastFreeParticleIndex=0;

    if (particles[lastFreeParticleIndex].life==0)
    {
      particles[lastFreeParticleIndex].life=maxLife;
      particles[lastFreeParticleIndex].x = x;
      particles[lastFreeParticleIndex].y = y;
      particles[lastFreeParticleIndex].vx = dx;
      particles[lastFreeParticleIndex].vy = dy;
      particles[lastFreeParticleIndex].addRandomVelocity();
      particles[lastFreeParticleIndex].r = r-(random(1.0f)*10.0f);
      particles[lastFreeParticleIndex].g = g-(random(1.0f)*40.0f);
      particles[lastFreeParticleIndex].b = b-(random(1.0f)*20.0f);
    }

    lastFreeParticleIndex++;
  }
}

class particle
{
  float x,y,vx,vy;
  float r,g,b;
  int life;

  void process()
  {
    //if (!mousePressed)
    {
      applyForces(0.0,gravity);
    }

    draw();
    life--;
  }

  void addRandomVelocity()
  {
    float angle = random(6.282f);
    float randomFactor = random(0.5f)+0.5f;
    vx += sin(angle) * startSpeed * randomFactor;
    vy += cos(angle) * startSpeed * randomFactor;
  }

  void applyForces(float fx, float fy)
  {
    vx+=fx;
    vy+=fy;
    vx*=friction;
    vy*=friction;
    x+=vx;
    y+=vy;

    if (x<0)
    {
      x=-x;
      vx=vx*-0.7f;
    }

    if (x>400)
    {
      x=400-(400-x);
      vx=vx*-0.7f;
    }

    if (y>400)
    {
      y=400-(400-y);
      vy=vy*-0.5f;
    }
  }

  void draw()
  {
    float lightness = (float)life/(float)maxLife;
    lightness+=random(0.8f);
    stroke(r*lightness,g*lightness,b*lightness);

    if (lightness>0.8f)
    {
      line(x-2,y,x+2,y);
      line(x,y-2,x,y+2);
    }
    else if (lightness>0.4f)
    {
      line(x-1,y,x+1,y);
      line(x,y-1,x,y+1);
    }
    else
    point(x,y);
  }
}