SuperTowerDefense/Explosion.js at master · StrayStormStudios/SuperTowerDefense · GitHub

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/*Defines an explosion */
Explosion.id = 0; //master explosion id

/*Explosion Defines an explosion
 * @param {Point} position The initial x / y position of the explosion
 * @param {Number} initialRadius How big the explosion is when it first fires
 * @param {Number} fullSizeRadius how big is the full size radius?
 * @param {Integer} growthFrames How many frames does it take the explosion to grow?
 * @param {Number} initialAlpha The initial transparency of the explosion (0.0 clear, 1.0 opaque)
 * @param {Number} fullSizeAlpha What alpha should the explosion be when full?( 0.0-1.0)
 * @param {Number} fadeFrames   How many frames should the explosion last before fading?
 * @param {Number} finalAlpha What alpha should the explosion be before it fades (0.0-1.0)
 * @param {Integer} targetFrame What frame should we be before starting the animation?
 */
function Explosion(
  position,
  color,
  initialRadius,
  fullSizeRadius,
  growthFrames,
  initialAlpha,
  fullSizeAlpha,
  fadeFrames,
  finalAlpha,
  targetFrame
) {
  //id
  this.id = Explosion.id;
  Explosion.id++;

  //basic fields
  this.position = position;
  this.color = color;
  this.initialRadius = initialRadius;
  this.fullSizeRadius = fullSizeRadius;
  this.growthFrames = growthFrames;
  this.initialAlpha = initialAlpha;
  this.fullSizeAlpha = fullSizeAlpha;
  this.fadeFrames = fadeFrames;
  this.finalAlpha = finalAlpha;

  //arrays
  this.frame = targetFrame;
  this.radii = new Array();
  this.alphas = new Array();
  this.calculateArrays();
}

//calculates both radii and alpha arrays
Explosion.prototype.calculateArrays = function () {
  for (var i = 0; i < this.growthFrames; i++) {
    this.radii.push(
      this.initialRadius +
        1.0 *
          (this.fullSizeRadius - this.initialRadius) *
          (i / this.growthFrames)
    );

    this.alphas.push(
      this.initialAlpha +
        1.0 * (this.fullSizeAlpha - this.initialAlpha) * (i / this.growthFrames)
    );
  }
  for (var i = 0; i <= this.fadeFrames; i++) {
    this.radii.push(this.fullSizeRadius);
    this.alphas.push(
      this.fullSizeAlpha +
        1.0 * (this.finalAlpha - this.fullSizeAlpha) * (i / this.fadeFrames)
    );
  }
};

/*draws the explosion
 * @param {Canvas Rendering Context} ctx
 * @return {Boolean} true if this should be deleted, false if not
 */
Explosion.prototype.draw = function (ctx) {
  var index = SuperTower.frame - this.frame;
  if (index >= 0) {
    if (index >= this.radii.length) {
      return true;
    }
    ctx.save();
    //console.log(this.radii[index]);
    ctx.translate(this.position.x, this.position.y);
    ctx.fillStyle = this.color;
    ctx.globalAlpha = this.alphas[index];
    ctx.beginPath();
    ctx.arc(0, 0, this.radii[index], 0, 2 * Math.PI);
    ctx.closePath();
    ctx.fill();
    ctx.restore();
    return false;
  }
};