chrome/browser/resources/pdf/zoom_manager.js

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import {NativeEventTarget as EventTarget} from 'chrome://resources/js/cr/event_target.m.js';

import {BrowserApi, ZoomBehavior} from './browser_api.js';

// Abstract parent of classes that manage updating the browser with zoom changes
// and/or updating the viewer's zoom when the browser zoom changes.
export class ZoomManager {
  /**
   * @param {function():number} getViewportZoom Callback to get the viewport's
   *     current zoom level.
   * @param {number} initialZoom The initial browser zoom level.
   */
  constructor(getViewportZoom, initialZoom) {
    if (this.constructor === ZoomManager) {
      throw new TypeError('Instantiated abstract class: ZoomManager');
    }

    /** @private {number} */
    this.browserZoom_ = initialZoom;

    /** @private {function():number} */
    this.getViewportZoom_ = getViewportZoom;

    /** @private {!EventTarget} */
    this.eventTarget_ = new EventTarget();
  }

  /** @return {!EventTarget} */
  getEventTarget() {
    return this.eventTarget_;
  }

  /**
   * Creates the appropriate kind of zoom manager given the zoom behavior.
   * @param {ZoomBehavior} zoomBehavior How to manage zoom.
   * @param {function():number} getViewportZoom A function that gets the current
   *     viewport zoom.
   * @param {function(number):Promise} setBrowserZoomFunction A function that
   *     sets the browser zoom to the provided value.
   * @param {number} initialZoom The initial browser zoom level.
   */
  static create(
      zoomBehavior, getViewportZoom, setBrowserZoomFunction, initialZoom) {
    switch (zoomBehavior) {
      case ZoomBehavior.MANAGE:
        return new ActiveZoomManager(
            getViewportZoom, setBrowserZoomFunction, initialZoom);
      case ZoomBehavior.PROPAGATE_PARENT:
        return new EmbeddedZoomManager(getViewportZoom, initialZoom);
      default:
        return new InactiveZoomManager(getViewportZoom, initialZoom);
    }
  }

  /**
   * Invoked when a browser-initiated zoom-level change occurs.
   * @param {number} newZoom the zoom level to zoom to.
   */
  onBrowserZoomChange(newZoom) {}

  /** Invoked when an extension-initiated zoom-level change occurs. */
  onPdfZoomChange() {}

  /**
   * Combines the internal pdf zoom and the browser zoom to
   * produce the total zoom level for the viewer.
   * @param {number} internalZoom the zoom level internal to the viewer.
   * @return {number} the total zoom level.
   */
  applyBrowserZoom(internalZoom) {
    return this.browserZoom_ * internalZoom;
  }

  /**
   * Given a zoom level, return the internal zoom level needed to
   * produce that zoom level.
   * @param {number} totalZoom the total zoom level.
   * @return {number} the zoom level internal to the viewer.
   */
  internalZoomComponent(totalZoom) {
    return totalZoom / this.browserZoom_;
  }

  /**
   * Returns whether two numbers are approximately equal.
   * @param {number} a The first number.
   * @param {number} b The second number.
   */
  floatingPointEquals(a, b) {
    const MIN_ZOOM_DELTA = 0.01;
    // If the zoom level is close enough to the current zoom level, don't
    // change it. This avoids us getting into an infinite loop of zoom changes
    // due to floating point error.
    return Math.abs(a - b) <= MIN_ZOOM_DELTA;
  }
}

// Has no control over the browser's zoom and does not respond to browser zoom
// changes.
export class InactiveZoomManager extends ZoomManager {}

// ActiveZoomManager controls the browser's zoom.
class ActiveZoomManager extends ZoomManager {
  /**
   * Constructs a ActiveZoomManager.
   * @param {function():number} getViewportZoom A function that gets the current
   *     viewport zoom level
   * @param {function(number):Promise} setBrowserZoomFunction A function that
   *     sets the browser zoom to the provided value.
   * @param {number} initialZoom The initial browser zoom level.
   */
  constructor(getViewportZoom, setBrowserZoomFunction, initialZoom) {
    super(getViewportZoom, initialZoom);

    /** @private {function(number):Promise} */
    this.setBrowserZoomFunction_ = setBrowserZoomFunction;

    /** @private {?Promise} */
    this.changingBrowserZoom_ = null;
  }

  /**
   * Invoked when a browser-initiated zoom-level change occurs.
   * @param {number} newZoom the zoom level to zoom to.
   */
  onBrowserZoomChange(newZoom) {
    // If we are changing the browser zoom level, ignore any browser zoom level
    // change events. Either, the change occurred before our update and will be
    // overwritten, or the change being reported is the change we are making,
    // which we have already handled.
    if (this.changingBrowserZoom_) {
      return;
    }

    if (this.floatingPointEquals(this.browserZoom_, newZoom)) {
      return;
    }

    this.browserZoom_ = newZoom;
    this.eventTarget_.dispatchEvent(
        new CustomEvent('set-zoom', {detail: newZoom}));
  }

  /**
   * Invoked when an extension-initiated zoom-level change occurs.
   * @override
   */
  onPdfZoomChange() {
    // If we are already changing the browser zoom level in response to a
    // previous extension-initiated zoom-level change, ignore this zoom change.
    // Once the browser zoom level is changed, we check whether the extension's
    // zoom level matches the most recently sent zoom level.
    if (this.changingBrowserZoom_) {
      return;
    }

    const viewportZoom = this.getViewportZoom_();
    if (this.floatingPointEquals(this.browserZoom_, viewportZoom)) {
      return;
    }

    this.changingBrowserZoom_ =
        this.setBrowserZoomFunction_(viewportZoom).then(() => {
          this.browserZoom_ = viewportZoom;
          this.changingBrowserZoom_ = null;

          // The extension's zoom level may have changed while the browser zoom
          // change was in progress. We call back into onPdfZoomChange to ensure
          // the browser zoom is up to date.
          this.onPdfZoomChange();
        });
  }

  /**
   * Combines the internal pdf zoom and the browser zoom to
   * produce the total zoom level for the viewer.
   * @param {number} internalZoom the zoom level internal to the viewer.
   * @return {number} the total zoom level.
   */
  applyBrowserZoom(internalZoom) {
    // The internal zoom and browser zoom are changed together, so the
    // browser zoom is already applied.
    return internalZoom;
  }

  /**
   * Given a zoom level, return the internal zoom level needed to
   * produce that zoom level.
   * @param {number} totalZoom the total zoom level.
   * @return {number} the zoom level internal to the viewer.
   */
  internalZoomComponent(totalZoom) {
    // The internal zoom and browser zoom are changed together, so the
    // internal zoom is the total zoom.
    return totalZoom;
  }
}

// Responds to changes in the browser zoom, but does not control the browser
// zoom.
class EmbeddedZoomManager extends ZoomManager {
  /**
   * Invoked when a browser-initiated zoom-level change occurs.
   * @param {number} newZoom the new browser zoom level.
   */
  onBrowserZoomChange(newZoom) {
    const oldZoom = this.browserZoom_;
    this.browserZoom_ = newZoom;
    this.eventTarget_.dispatchEvent(
        new CustomEvent('update-zoom-from-browser', {detail: oldZoom}));
  }
}