void setup()
{size (600, 600);
 
stroke(250);
}
void loop()

{
background(0, mouseX, -mouseX);

for(int mouseY=0; mouseY<500; mouseY=mouseY+5) { 
  line(mouseX+mouseY, mouseY, mouseX+mouseX, mouseY+mouseY);    
}

  
  ellipse (mouseX, mouseY, 20, 20);


}