waterDrop[] rain;
int maxSlope = 3;
int numOfDrops = 1000;

void setup(){
  size(640,480);
  rain = new waterDrop[numOfDrops];
  for(int i = 0; i < numOfDrops; i++){ 
    // - - - - - - - - - - - - - - - Where to Start X - Drop Size - Drop Speed - -
    rain[i] = new waterDrop(random(10,width-10),random(3,15),random(3,8));
  }
  frameRate(30);
  smooth();
}

void draw(){
  background(255);
  for(int i = 0; i < numOfDrops; i++){
    rain[i].display();
    rain[i].drop(mouseY, mouseX);
  }


}

class waterDrop {
  float dropWidth;
  float dropHeight;
  float xStart;
  float dropSpeed, speedMod;
  float dropSlope, beginX, beginY, endX, endY;

  waterDrop(float iX, float iXY, float iS){
    beginX = iX;
    dropHeight = iXY;
    dropWidth = iXY/2.5;
    dropSpeed = iS;
  }

  void drop(int theY, int theX){
    dropSlope = map(theX, 0, width, 0, maxSlope);
    speedMod = map(theY, 0, height, 1, 2.25);
    //Random to keep from a vertical stripe of rain
    if(theX < (beginX - random(1,25))){
      endX = beginX;
      beginX = beginX - dropSlope;
    }
    if(theX > (beginX + random(1,25))){
      endX = beginX;
      beginX = beginX + dropSlope;
    }
    beginY = beginY + (dropSpeed * speedMod);
    endY = beginY - dropHeight;
    if(beginY >= height){
      beginY = 0;
      endY = 0;
      beginX = random(10,width-10);
    }
  }

  void display(){
    //Catch the weird math errors
    if(abs(beginX-endX) > 10){
      endX = beginX;
    }
    line(beginX, beginY, endX, endY);
  }

}