why-cant-we-deploy-today/js/controllers/pointer.js

/**
 * Handles hiding of the pointer/cursor when inactive.
 */
export default class Pointer {
  constructor(Reveal) {
    this.Reveal = Reveal;

    // Throttles mouse wheel navigation
    this.lastMouseWheelStep = 0;

    // Is the mouse pointer currently hidden from view
    this.cursorHidden = false;

    // Timeout used to determine when the cursor is inactive
    this.cursorInactiveTimeout = 0;

    this.onDocumentCursorActive = this.onDocumentCursorActive.bind(this);
    this.onDocumentMouseScroll = this.onDocumentMouseScroll.bind(this);
  }

  /**
   * Called when the reveal.js config is updated.
   */
  configure(config, oldConfig) {
    if (config.mouseWheel) {
      document.addEventListener(
        "DOMMouseScroll",
        this.onDocumentMouseScroll,
        false
      ); // FF
      document.addEventListener(
        "mousewheel",
        this.onDocumentMouseScroll,
        false
      );
    } else {
      document.removeEventListener(
        "DOMMouseScroll",
        this.onDocumentMouseScroll,
        false
      ); // FF
      document.removeEventListener(
        "mousewheel",
        this.onDocumentMouseScroll,
        false
      );
    }

    // Auto-hide the mouse pointer when its inactive
    if (config.hideInactiveCursor) {
      document.addEventListener(
        "mousemove",
        this.onDocumentCursorActive,
        false
      );
      document.addEventListener(
        "mousedown",
        this.onDocumentCursorActive,
        false
      );
    } else {
      this.showCursor();

      document.removeEventListener(
        "mousemove",
        this.onDocumentCursorActive,
        false
      );
      document.removeEventListener(
        "mousedown",
        this.onDocumentCursorActive,
        false
      );
    }
  }

  /**
   * Shows the mouse pointer after it has been hidden with
   * #hideCursor.
   */
  showCursor() {
    if (this.cursorHidden) {
      this.cursorHidden = false;
      this.Reveal.getRevealElement().style.cursor = "";
    }
  }

  /**
   * Hides the mouse pointer when it's on top of the .reveal
   * container.
   */
  hideCursor() {
    if (this.cursorHidden === false) {
      this.cursorHidden = true;
      this.Reveal.getRevealElement().style.cursor = "none";
    }
  }

  destroy() {
    this.showCursor();

    document.removeEventListener(
      "DOMMouseScroll",
      this.onDocumentMouseScroll,
      false
    );
    document.removeEventListener(
      "mousewheel",
      this.onDocumentMouseScroll,
      false
    );
    document.removeEventListener(
      "mousemove",
      this.onDocumentCursorActive,
      false
    );
    document.removeEventListener(
      "mousedown",
      this.onDocumentCursorActive,
      false
    );
  }

  /**
   * Called whenever there is mouse input at the document level
   * to determine if the cursor is active or not.
   *
   * @param {object} event
   */
  onDocumentCursorActive(event) {
    this.showCursor();

    clearTimeout(this.cursorInactiveTimeout);

    this.cursorInactiveTimeout = setTimeout(
      this.hideCursor.bind(this),
      this.Reveal.getConfig().hideCursorTime
    );
  }

  /**
   * Handles mouse wheel scrolling, throttled to avoid skipping
   * multiple slides.
   *
   * @param {object} event
   */
  onDocumentMouseScroll(event) {
    if (Date.now() - this.lastMouseWheelStep > 1000) {
      this.lastMouseWheelStep = Date.now();

      let delta = event.detail || -event.wheelDelta;
      if (delta > 0) {
        this.Reveal.next();
      } else if (delta < 0) {
        this.Reveal.prev();
      }
    }
  }
}