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355 lines
9.0 KiB
HTML
355 lines
9.0 KiB
HTML
<!--
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@license
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Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
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This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
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The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
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The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
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Code distributed by Google as part of the polymer project is also
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subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
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-->
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<link rel="import" href="../polymer/polymer.html">
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<link rel="import" href="../iron-flex-layout/classes/iron-flex-layout.html">
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<!--
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`iron-image` is an element for displaying an image that provides useful sizing and
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preloading options not found on the standard `<img>` tag.
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The `sizing` option allows the image to be either cropped (`cover`) or
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letterboxed (`contain`) to fill a fixed user-size placed on the element.
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The `preload` option prevents the browser from rendering the image until the
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image is fully loaded. In the interim, either the element's CSS `background-color`
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can be be used as the placeholder, or the `placeholder` property can be
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set to a URL (preferably a data-URI, for instant rendering) for an
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placeholder image.
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The `fade` option (only valid when `preload` is set) will cause the placeholder
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image/color to be faded out once the image is rendered.
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Examples:
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Basically identical to <img src="..."> tag:
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<iron-image src="http://lorempixel.com/400/400"></iron-image>
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Will letterbox the image to fit:
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<iron-image style="width:400px; height:400px;" sizing="contain"
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src="http://lorempixel.com/600/400"></iron-image>
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Will crop the image to fit:
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<iron-image style="width:400px; height:400px;" sizing="cover"
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src="http://lorempixel.com/600/400"></iron-image>
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Will show light-gray background until the image loads:
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<iron-image style="width:400px; height:400px; background-color: lightgray;"
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sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image>
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Will show a base-64 encoded placeholder image until the image loads:
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<iron-image style="width:400px; height:400px;" placeholder="data:image/gif;base64,..."
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sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image>
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Will fade the light-gray background out once the image is loaded:
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<iron-image style="width:400px; height:400px; background-color: lightgray;"
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sizing="cover" preload fade src="http://lorempixel.com/600/400"></iron-image>
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@group Iron Elements
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@element iron-image
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@demo demo/index.html
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-->
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<dom-module id="iron-image">
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<style>
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:host {
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display: inline-block;
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overflow: hidden;
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position: relative;
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}
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:host([sizing]) #img {
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display: none;
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}
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#placeholder {
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background-color: inherit;
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opacity: 1;
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}
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#placeholder.faded-out {
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transition: opacity 0.5s linear;
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opacity: 0;
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}
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</style>
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<template>
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<img id="img" role="none" hidden$="[[_computeImageVisibility(sizing)]]">
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<div id="placeholder" hidden$="[[_computePlaceholderVisibility(fade,loaded,preload)]]" class$="[[_computePlaceholderClassName(fade,loaded,preload)]]"></div>
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<content></content>
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</template>
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</dom-module>
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<script>
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Polymer({
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is: 'iron-image',
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properties: {
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/**
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* The URL of an image.
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*/
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src: {
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observer: '_srcChanged',
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type: String,
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value: ''
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},
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/**
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* When true, the image is prevented from loading and any placeholder is
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* shown. This may be useful when a binding to the src property is known to
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* be invalid, to prevent 404 requests.
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*/
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preventLoad: {
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type: Boolean,
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value: false
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},
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/**
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* Sets a sizing option for the image. Valid values are `contain` (full
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* aspect ratio of the image is contained within the element and
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* letterboxed) or `cover` (image is cropped in order to fully cover the
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* bounds of the element), or `null` (default: image takes natural size).
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*/
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sizing: {
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type: String,
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value: null
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},
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/**
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* When a sizing option is uzed (`cover` or `contain`), this determines
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* how the image is aligned within the element bounds.
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*/
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position: {
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type: String,
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value: 'center'
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},
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/**
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* When `true`, any change to the `src` property will cause the `placeholder`
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* image to be shown until the
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*/
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preload: {
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type: Boolean,
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value: false
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},
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/**
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* This image will be used as a background/placeholder until the src image has
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* loaded. Use of a data-URI for placeholder is encouraged for instant rendering.
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*/
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placeholder: {
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type: String,
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value: null
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},
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/**
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* When `preload` is true, setting `fade` to true will cause the image to
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* fade into place.
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*/
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fade: {
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type: Boolean,
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value: false
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},
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/**
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* Read-only value that is true when the image is loaded.
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*/
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loaded: {
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notify: true,
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type: Boolean,
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value: false
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},
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/**
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* Read-only value that tracks the loading state of the image when the `preload`
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* option is used.
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*/
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loading: {
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notify: true,
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type: Boolean,
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value: false
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},
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/**
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* Can be used to set the width of image (e.g. via binding); size may also be
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* set via CSS.
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*/
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width: {
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observer: '_widthChanged',
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type: Number,
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value: null
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},
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/**
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* Can be used to set the height of image (e.g. via binding); size may also be
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* set via CSS.
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*
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* @attribute height
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* @type number
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* @default null
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*/
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height: {
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observer: '_heightChanged',
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type: Number,
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value: null
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},
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_placeholderBackgroundUrl: {
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type: String,
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computed: '_computePlaceholderBackgroundUrl(preload,placeholder)',
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observer: '_placeholderBackgroundUrlChanged'
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},
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requiresPreload: {
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type: Boolean,
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computed: '_computeRequiresPreload(preload,loaded)'
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},
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canLoad: {
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type: Boolean,
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computed: '_computeCanLoad(preventLoad, src)'
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}
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},
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observers: [
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'_transformChanged(sizing, position)',
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'_loadBehaviorChanged(canLoad, preload, loaded)',
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'_loadStateChanged(src, preload, loaded)',
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],
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ready: function() {
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if (!this.hasAttribute('role')) {
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this.setAttribute('role', 'img');
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}
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},
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_computeImageVisibility: function() {
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return !!this.sizing;
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},
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_computePlaceholderVisibility: function() {
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return !this.preload || (this.loaded && !this.fade);
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},
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_computePlaceholderClassName: function() {
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if (!this.preload) {
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return '';
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}
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var className = 'fit';
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if (this.loaded && this.fade) {
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className += ' faded-out';
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}
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return className;
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},
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_computePlaceholderBackgroundUrl: function() {
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if (this.preload && this.placeholder) {
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return 'url(' + this.placeholder + ')';
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}
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return null;
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},
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_computeRequiresPreload: function() {
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return this.preload && !this.loaded;
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},
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_computeCanLoad: function() {
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return Boolean(!this.preventLoad && this.src);
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},
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_widthChanged: function() {
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this.style.width = isNaN(this.width) ? this.width : this.width + 'px';
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},
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_heightChanged: function() {
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this.style.height = isNaN(this.height) ? this.height : this.height + 'px';
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},
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_srcChanged: function(newSrc, oldSrc) {
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if (newSrc !== oldSrc) {
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this.loaded = false;
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}
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},
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_placeholderBackgroundUrlChanged: function() {
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this.$.placeholder.style.backgroundImage =
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this._placeholderBackgroundUrl;
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},
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_transformChanged: function() {
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var placeholderStyle = this.$.placeholder.style;
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this.style.backgroundSize =
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placeholderStyle.backgroundSize = this.sizing;
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this.style.backgroundPosition =
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placeholderStyle.backgroundPosition =
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this.sizing ? this.position : '';
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this.style.backgroundRepeat =
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placeholderStyle.backgroundRepeat =
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this.sizing ? 'no-repeat' : '';
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},
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_loadBehaviorChanged: function() {
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var img;
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if (!this.canLoad) {
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return;
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}
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if (this.requiresPreload) {
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img = new Image();
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img.src = this.src;
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this.loading = true;
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img.onload = function() {
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this.loading = false;
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this.loaded = true;
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}.bind(this);
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} else {
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this.loaded = true;
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}
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},
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_loadStateChanged: function() {
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if (this.requiresPreload) {
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return;
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}
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if (this.sizing) {
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this.style.backgroundImage = this.src ? 'url(' + this.src + ')': '';
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} else {
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this.$.img.src = this.src || '';
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}
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}
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});
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</script>
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