Snowflake[] snowflakes = new Snowflake[2000];
int lastFlakeIndex = -1;

void setup() {
  size(640, 480);
  
  for (int i = 0; i <= 100; i++) {
    spawnNewFlake();
    snowflakes[i].setY(random(height / 4));
  }
}

void draw() {
  background(0);
  
  drawChristmasTree();
  
  for (Snowflake flake : snowflakes) {
    if (flake == null) continue;
    
    flake.update();
    flake.draw();
  }
  
  spawnNewFlake();
}

boolean canFallTo(int x, int y, float offset) {
  if (y >= height - offset) return false;
  
  color pixel = get(x, y);
  
  return pixel != #640909 &&
         pixel != #FFFF00 &&
         pixel != #1B7110 &&
         pixel != #FF0000 &&
         pixel != #990000;
}

void drawChristmasTree() {
  noStroke();
  
  fill(#640909);
  rect(width / 2 - 10, height - 25, 20, 25);
  
  drawBranches(width / 2 - 100, height - 25, width / 2 + 100, height - 25, width / 2, height - 75, 3);
  drawBranches(width / 2 - 80, height - 50, width / 2 + 80, height - 50, width / 2, height - 100, 3);
  drawBranches(width / 2 - 60, height - 75, width / 2 + 60, height - 75, width / 2, height - 125, 2);
  drawBranches(width / 2 - 40, height - 100, width / 2 + 40, height - 100, width / 2, height - 150, 2);
  drawBranches(width / 2 - 30, height - 125, width / 2 + 30, height - 125, width / 2, height - 160, 2);
  
  fill(#FFFF00);
  drawStar(width / 2, height - 160, 20, 10, 6);
}

void drawBranches(int x1, int y1, int x2, int y2, int x3, int y3, int mod) {
  fill(#1B7110);
  triangle(x1, y1, x2, y2, x3, y3);
  
  for (int i = x1 + 10; i <= x2 - 10; i += 10) {
    fill(#FF0000);
    if ((i/10) % mod == 0) {
      fill(#990000);
    }
    circle(i, y1, 7);
  }
}

void drawStar(float x, float y, float radius1, float radius2, int nPoints) {
  float angle = TWO_PI / nPoints;
  float halfAngle = angle / 2.0;
  
  beginShape();
  
  for (float a = 0; a < TWO_PI; a += angle) {
    float sx = x + cos(a) * radius2;
    float sy = y + sin(a) * radius2;
    
    vertex(sx, sy);
    
    sx = x + cos(a + halfAngle) * radius1;
    sy = y + sin(a + halfAngle) * radius1;
    
    vertex(sx, sy);
  }
  
  endShape(CLOSE);
}

void spawnNewFlake() {
  lastFlakeIndex++;
  
  if (lastFlakeIndex >= snowflakes.length) {
    lastFlakeIndex = 0;
  }
  
  int rg = 255 - int(random(96));
  snowflakes[lastFlakeIndex] = new Snowflake(random(width), 0, 0.5 + random(1), 2 + random(3), color(rg, rg, 255));
}