float y1;                 //variable to hold the lineStart
float y2;                 //variable to hold the lineEnd
int x1;                   //variable to hold the x-positions
int x2;
int col;                  //variable for alpha strength
float lineHeight;         //Sets maximum value
float distance;
float closeEnough = 50;        //Sets variable for when lines begin to grow


void setup(){
  size(720,240);
  background(0);
  stroke(255,50);
  x1=(width/2);
  x2=(width/2);


}
void draw(){
  background(0);
  setLineHeight();
  drawLine();
}


void setLineHeight(){
  distance=abs(mouseX-x1);
  if (distance <= closeEnough){
    if(distance <= 0){
        lineHeight=(height/2)-70;   //if 0, set MAXIMUM line Height
      }else{
        lineHeight = ((height/2)-70)+distance;   //setting LINE HEIGHT based on DISTANCE
      }
    }else{
      lineHeight=(height/2)-30;    //if mouse too far away, set MINIMUM line Height
    }
}


void drawLine(){
  for(int i = 0; i < (width/10); i++){  //decreasing will drop opacity of whole line
    if (lineHeight >= (height/2)){
      lineHeight = (height/2);  //Make sure lines don't draw past center
    }
    line(x1,y1,x2,y2);
    y1=lineHeight;        //Sets linestart to INCREASING value as loop goes
    y2=(height)-y1;       //Sets lineEnd to a DECREASING value as loop goes
    col = i+(round(width/lineHeight));              //TRANSPARENCY drops as you go up in loop
    lineHeight++;         
    stroke(255, col);
  }
}