/**
 * Animating a square.
 *
 * <p>Elie Zananiri<br>
 * CART 253, Winter 2008</p>
 */

/* global variables */
float rectX = 0;
float rectY = 50;
int rectSize = 50;

// this value is used to calculate the distance of the step
int easeFactor = 10;
float acceptableOffset = 0.001;
boolean goToTarget;
float startX;
float startY;
float targetX;
float targetY;

color currColor;
color idleColor;
color activeColor;

/* built-in functions */
void setup() {
  size(300, 300);
  rectMode(CENTER);
  colorMode(HSB, 360, 100, 100);  // use the same ranges as the color selector
  noStroke();
  smooth();
  
  goToTarget = false;
  
  idleColor = color(54, 98, 98);   // yellow
  activeColor = color(2, 98, 97);  // red
}

void draw() {
  // motion blur
  fill(0, 30);
  rect(width/2, height/2, width, height);
  
  if (goToTarget) moveSquare();
  colorSquare();
  drawSquare();
}

void mousePressed() {
  // save the starting position
  startX = rectX;
  startY = rectY;
  // save the target position
  targetX = mouseX;
  targetY = mouseY;

  goToTarget = true;
}

/* custom functions */
// moves the square
void moveSquare() {
  // find the distance from the mouse click to the square
  float dX = targetX-rectX;
  float dY = targetY-rectY;
  
  // ease towards the target
  float stepX = dX/easeFactor;
  float stepY = dY/easeFactor;
  
  // set the new square position
  rectX += stepX;
  rectY += stepY;
  
  // check if the distance is small enough to consider it having arrived at the target
  if (abs(dX) <= acceptableOffset && abs(dY) <= acceptableOffset) {
    goToTarget = false;
  }
}

// calculates the color ratio based on position
void colorSquare() {
  float ratioX = (rectX-startX)/(targetX-startX);
  float ratioY = (rectY-startY)/(targetY-startY);
  float ratioAvg = (ratioX+ratioY)/2;
  currColor = lerpColor(idleColor, activeColor, ratioAvg);
}

// draws the square
void drawSquare() {
  fill(currColor);
  rect(rectX, rectY, rectSize, rectSize);
}