/* built with Studio Sketchpad: 
 *   https://sketchpad.cc
 * 
 * observe the evolution of this sketch: 
 *   https://studio.sketchpad.cc/sp/pad/view/ro.ewgZEbTsJde/rev.967
 * 
 * authors: 
 *   Doug Park

 * license (unless otherwise specified): 
 *   creative commons attribution-share alike 3.0 license.
 *   https://creativecommons.org/licenses/by-sa/3.0/ 
 */ 



// This sketch builds on a prior work, "Lines of March", created by Doug Park
// http://studio.sketchpad.cc/sp/pad/view/ro.9o7Pwz5qhoLlT/rev.597

// height and width are built in global variables automatically set based on the canvas size.

// Lines Marching
// March 11, 2012
// Lines marching across the screen

  // create a line counter to clear the screen every so often
  counter = 0;

// This runs once to setup the program
void setup() {
    
  // set canvis size to a big 500x500 pixel   
  size(500, 500);
  
  // make the background white 
  background(255); 
  
  // call a function to set the initial color of the lines
  changeColor();
   
  // setup the line
  x1 = random(width);
  x2 = random(width);
  y1 = random(height);
  y2 = random(height);
  
  // setup delta offset, each end point of the line will move independently
  dx1 = random(9)+1;
  dx2 = random(9)+1;
  dy1 = random(9)+1;
  dy2 = random(9)+1;
  
  // set the width of the line. 
    strokeWeight(1);
}

// This runs in a continious loop
void draw() {
        
   // draw a line based on the x1,y1 and x2,y2 endpoints
   line (x1, y1, x2, y2);
   
   
   // Move the endpoints of the line based on their delta offset
   x1 = x1 + dx1;
   y1 = y1 + dy1;
   
   x2 = x2 + dx2;
   y2 = y2 + dy2;
   
   // check if the endpoint of the line hits a screen boundry
   // if it does then reverse the delta offset for that line endpoint
   // also change the color of the line to keep things interesting
   if (x1 <= 0) { dx1 = - dx1; changeColor() };
   if (x1 >= width) { dx1 = - dx1; changeColor() };
   if (x2 <= 0) { dx2 = - dx2; changeColor() };
   if (x2 >= width) { dx2 = - dx2; changeColor() };
   if (y1 <= 0) { dy1 = - dy1; changeColor() };
   if (y1 >= height) { dy1 = - dy1; changeColor() };
   if (y2 <= 0) { dy2 = - dy2; changeColor() };
   if (y2 >= height) { dy2 = - dy2; changeColor() };
   
   // check the line counter to see if it is time to clear the screen
   if (counter > random(200) + 500) { background(255); counter = 0; };
   counter = counter + 1;
   
}

// change the color of the line everytime an endpoint hits a screen boundry
void changeColor() {
    
   stroke (random(50),random(255), random(255)); 
    
    }