/**
 * Motion blur on an animated square.
 *
 * <p>Elie Zananiri<br>
 * CART 253, Winter 2008</p>
 */

/* global variables */
int rectX = 0;
int rectY = 50;
int rectSize = 50;
// this value is used to calculate the distance of the step but
// also to determine the minimum offset to reach the target
int easeFactor = 10;
int targetLeft;
int targetRight;
int currTarget;

/* built-in functions */
void setup() {
  size(300, 300);
  noStroke();
  smooth();
  
  targetLeft = 0;
  targetRight = width-rectSize;
  setTarget(targetLeft);
}

void draw() {
  fill(0, 30);
  rect(0, 0, width, height);
  
  moveSquare();
  drawSquare();
}

/* custom functions */
// sets the target x position of the square
void setTarget(int newTarget) {
  currTarget = newTarget; 
}

// moves the square
void moveSquare() {
  // find the distance from the target to the square
  int dX = currTarget-rectX;
  
  // ease towards the target
  int stepX = dX/easeFactor;
  
  // set the new square position
  rectX += stepX;
  
  // check if the step is small enough to consider it having arrived at the target
  if ((rectX-targetLeft) <= easeFactor) {
    setTarget(targetRight);
  } else if ((targetRight-rectX) <= easeFactor) {
    setTarget(targetLeft); 
  }
}

// draws the square
void drawSquare() {
  fill(255, 128, 0);  // orange
  rect(rectX, rectY, rectSize, rectSize);
}