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// Copyright 2013 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/**
* @fileoverview Utility class that monitors pixel density ratio changes.
*
* @see ../demos/pixeldensitymonitor.html
*/
goog.provide('goog.labs.style.PixelDensityMonitor');
goog.provide('goog.labs.style.PixelDensityMonitor.Density');
goog.provide('goog.labs.style.PixelDensityMonitor.EventType');
goog.require('goog.events');
goog.require('goog.events.EventTarget');
/**
* Monitors the window for changes to the ratio between device and screen
* pixels, e.g. when the user moves the window from a high density screen to a
* screen with normal density. Dispatches
* goog.labs.style.PixelDensityMonitor.EventType.CHANGE events when the density
* changes between the two predefined values NORMAL and HIGH.
*
* This class uses the window.devicePixelRatio value which is supported in
* WebKit and FF18. If the value does not exist, it will always return a
* NORMAL density. It requires support for MediaQueryList to detect changes to
* the devicePixelRatio.
*
* @param {!goog.dom.DomHelper=} opt_domHelper The DomHelper which contains the
* document associated with the window to listen to. Defaults to the one in
* which this code is executing.
* @constructor
* @extends {goog.events.EventTarget}
* @final
*/
goog.labs.style.PixelDensityMonitor = function(opt_domHelper) {
goog.labs.style.PixelDensityMonitor.base(this, 'constructor');
/**
* @type {Window}
* @private
*/
this.window_ = opt_domHelper ? opt_domHelper.getWindow() : window;
/**
* The last density that was reported so that changes can be detected.
* @type {goog.labs.style.PixelDensityMonitor.Density}
* @private
*/
this.lastDensity_ = this.getDensity();
/**
* @type {function (MediaQueryList)}
* @private
*/
this.listener_ = goog.bind(this.handleMediaQueryChange_, this);
/**
* The media query list for a query that detects high density, if supported
* by the browser. Because matchMedia returns a new object for every call, it
* needs to be saved here so the listener can be removed when disposing.
* @type {?MediaQueryList}
* @private
*/
this.mediaQueryList_ = this.window_.matchMedia ?
this.window_.matchMedia(
goog.labs.style.PixelDensityMonitor.HIGH_DENSITY_QUERY_) :
null;
};
goog.inherits(goog.labs.style.PixelDensityMonitor, goog.events.EventTarget);
/**
* The two different pixel density modes on which the various ratios between
* physical and device pixels are mapped.
* @enum {number}
*/
goog.labs.style.PixelDensityMonitor.Density = {
/**
* Mode for older portable devices and desktop screens, defined as having a
* device pixel ratio of less than 1.5.
*/
NORMAL: 1,
/**
* Mode for newer portable devices with a high resolution screen, defined as
* having a device pixel ratio of more than 1.5.
*/
HIGH: 2
};
/**
* The events fired by the PixelDensityMonitor.
* @enum {string}
*/
goog.labs.style.PixelDensityMonitor.EventType = {
/**
* Dispatched when density changes between NORMAL and HIGH.
*/
CHANGE: goog.events.getUniqueId('change')
};
/**
* Minimum ratio between device and screen pixel needed for high density mode.
* @type {number}
* @private
*/
goog.labs.style.PixelDensityMonitor.HIGH_DENSITY_RATIO_ = 1.5;
/**
* Media query that matches for high density.
* @type {string}
* @private
*/
goog.labs.style.PixelDensityMonitor.HIGH_DENSITY_QUERY_ =
'(min-resolution: 1.5dppx), (-webkit-min-device-pixel-ratio: 1.5)';
/**
* Starts monitoring for changes in pixel density.
*/
goog.labs.style.PixelDensityMonitor.prototype.start = function() {
if (this.mediaQueryList_) {
this.mediaQueryList_.addListener(this.listener_);
}
};
/**
* @return {goog.labs.style.PixelDensityMonitor.Density} The density for the
* window.
*/
goog.labs.style.PixelDensityMonitor.prototype.getDensity = function() {
if (this.window_.devicePixelRatio >=
goog.labs.style.PixelDensityMonitor.HIGH_DENSITY_RATIO_) {
return goog.labs.style.PixelDensityMonitor.Density.HIGH;
} else {
return goog.labs.style.PixelDensityMonitor.Density.NORMAL;
}
};
/**
* Handles a change to the media query and checks whether the density has
* changed since the last call.
* @param {MediaQueryList} mql The list of changed media queries.
* @private
*/
goog.labs.style.PixelDensityMonitor.prototype.handleMediaQueryChange_ =
function(mql) {
var newDensity = this.getDensity();
if (this.lastDensity_ != newDensity) {
this.lastDensity_ = newDensity;
this.dispatchEvent(goog.labs.style.PixelDensityMonitor.EventType.CHANGE);
}
};
/** @override */
goog.labs.style.PixelDensityMonitor.prototype.disposeInternal = function() {
if (this.mediaQueryList_) {
this.mediaQueryList_.removeListener(this.listener_);
}
goog.labs.style.PixelDensityMonitor.base(this, 'disposeInternal');
};
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