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[rbdr/heart] / js / lib / heart_renderer.js

'use strict';

((window) => {

  const kColorIteratorLimit = 256;
  const kRedSpeed = 0.1;
  const kGreenSpeed = 0.2;
  const kBlueSpeed = 0.15;

  /**
   * Renders a Heart, has its own canvas, which will be placed in the element
   * set by calling #render.
   *
   * @class HeartRenderer
   * @param {object} config configuration, extends any member of the renderer
   */
  const HeartRenderer = class HeartRenderer {

    constructor(config) {

      /**
       * The instance of the heart renderer being used
       *
       * @memberof HeartRenderer
       * @instance
       * @name canvas
       * @type HTMLCanvasElement
       * @default A brand new full width and height canvas
       */
      this.canvas = window.document.createElement('canvas');
      this.canvas.style.height = '100%';
      this.canvas.style.width = '100%';

      /**
       * The maximum fps that will be used
       *
       * @memberof HeartRenderer
       * @instance
       * @name fps
       * @type Number
       * @default 60
       */
      this.fps = 60;

      this._animating = false; // The status of the animation.
      this._previousFrameTime = Date.now(); // The timestamp of the last frame for fps control
      this._currentColor = { // The current color that will be painted
        red: 100,
        blue: 0,
        green: 50
      };

      Object.assign(this, config);
    }

    /**
     * Attaches the canvas to an HTML element
     *
     * @memberof HeartRenderer
     * @function render
     * @instance
     * @param {HTMLElement} element the element where we will attach our canvas
     */
    render(element) {

      element.appendChild(this.canvas);
    }

    /**
     * Gets the context from the current canvas and starts the animation process
     *
     * @memberof HeartRenderer
     * @function activate
     * @instance
     */
    activate() {

      const context = this.canvas.getContext('2d');
      this._startAnimating(context);
    }

    /**
     * Stops the animation process
     *
     * @memberof HeartRenderer
     * @function deactivate
     * @instance
     */
    deactivate() {

      this._stopAnimating();
    }

    // Starts the animation loop
    _startAnimating(context) {

      this._frameDuration = 1000 / this.fps;
      this._animating = true;

      this._animate(context);
    }

    // Stops the animation on the next frame.
    _stopAnimating() {

      this._animating = false;
    }

    // Runs the animation step controlling the FPS
    _animate(context) {

      if (!this._animating) {
        return;
      }

      window.requestAnimationFrame(this._animate.bind(this, context));

      const currentFrameTime = Date.now();
      const delta = currentFrameTime - this._previousFrameTime;

      if (delta > this._frameDuration) {
        this._previousFrameTime = Date.now();
        this._animateStep(context, delta);
      }
    }

    // The actual animation processing function.
    _animateStep(context, delta) {

      this._currentColor.red = Math.round(this._currentColor.red + delta * kRedSpeed) % kColorIteratorLimit;
      this._currentColor.green = Math.round(this._currentColor.green + delta * kGreenSpeed) % kColorIteratorLimit;
      this._currentColor.blue = Math.round(this._currentColor.blue + delta * kBlueSpeed) % kColorIteratorLimit;

      context.fillStyle = `rgb(${this._currentColor.red}, ${this._currentColor.green}, ${this._currentColor.blue})`;
      context.fillRect(0, 0, this.canvas.scrollWidth, this.canvas.scrollHeight);
    }
  };


  window.HeartRenderer = HeartRenderer;
})(window);