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1 <!-- | |
2 @license | |
3 Copyright (c) 2015 The Polymer Project Authors. All rights reserved. | |
4 This code may only be used under the BSD style license found at http://polymer.g
ithub.io/LICENSE.txt | |
5 The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt | |
6 The complete set of contributors may be found at http://polymer.github.io/CONTRI
BUTORS.txt | |
7 Code distributed by Google as part of the polymer project is also | |
8 subject to an additional IP rights grant found at http://polymer.github.io/PATEN
TS.txt | |
9 --> | |
10 | |
11 <link rel="import" href="../polymer/polymer.html"> | |
12 <link rel="import" href="../iron-flex-layout/classes/iron-flex-layout.html"> | |
13 | |
14 <!-- | |
15 `iron-image` is an element for displaying an image that provides useful sizing a
nd | |
16 preloading options not found on the standard `<img>` tag. | |
17 | |
18 The `sizing` option allows the image to be either cropped (`cover`) or | |
19 letterboxed (`contain`) to fill a fixed user-size placed on the element. | |
20 | |
21 The `preload` option prevents the browser from rendering the image until the | |
22 image is fully loaded. In the interim, either the element's CSS `background-col
or` | |
23 can be be used as the placeholder, or the `placeholder` property can be | |
24 set to a URL (preferably a data-URI, for instant rendering) for an | |
25 placeholder image. | |
26 | |
27 The `fade` option (only valid when `preload` is set) will cause the placeholder | |
28 image/color to be faded out once the image is rendered. | |
29 | |
30 Examples: | |
31 | |
32 Basically identical to <img src="..."> tag: | |
33 | |
34 <iron-image src="http://lorempixel.com/400/400"></iron-image> | |
35 | |
36 Will letterbox the image to fit: | |
37 | |
38 <iron-image style="width:400px; height:400px;" sizing="contain" | |
39 src="http://lorempixel.com/600/400"></iron-image> | |
40 | |
41 Will crop the image to fit: | |
42 | |
43 <iron-image style="width:400px; height:400px;" sizing="cover" | |
44 src="http://lorempixel.com/600/400"></iron-image> | |
45 | |
46 Will show light-gray background until the image loads: | |
47 | |
48 <iron-image style="width:400px; height:400px; background-color: lightgray;" | |
49 sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image> | |
50 | |
51 Will show a base-64 encoded placeholder image until the image loads: | |
52 | |
53 <iron-image style="width:400px; height:400px;" placeholder="data:image/gif;b
ase64,..." | |
54 sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image> | |
55 | |
56 Will fade the light-gray background out once the image is loaded: | |
57 | |
58 <iron-image style="width:400px; height:400px; background-color: lightgray;" | |
59 sizing="cover" preload fade src="http://lorempixel.com/600/400"></iron-ima
ge> | |
60 | |
61 | |
62 @group Iron Elements | |
63 @element iron-image | |
64 @demo demo/index.html | |
65 --> | |
66 | |
67 <dom-module id="iron-image"> | |
68 | |
69 <style> | |
70 | |
71 :host { | |
72 display: inline-block; | |
73 overflow: hidden; | |
74 position: relative; | |
75 } | |
76 | |
77 :host([sizing]) #img { | |
78 display: none; | |
79 } | |
80 | |
81 #placeholder { | |
82 background-color: inherit; | |
83 opacity: 1; | |
84 } | |
85 | |
86 #placeholder.faded-out { | |
87 transition: opacity 0.5s linear; | |
88 opacity: 0; | |
89 } | |
90 | |
91 </style> | |
92 | |
93 <template> | |
94 | |
95 <img id="img" role="none" hidden$="[[_computeImageVisibility(sizing)]]"> | |
96 <div id="placeholder" hidden$="[[_computePlaceholderVisibility(fade,loaded,p
reload)]]" class$="[[_computePlaceholderClassName(fade,loaded,preload)]]"></div> | |
97 <content></content> | |
98 | |
99 </template> | |
100 | |
101 </dom-module> | |
102 | |
103 <script> | |
104 | |
105 Polymer({ | |
106 | |
107 is: 'iron-image', | |
108 | |
109 properties: { | |
110 /** | |
111 * The URL of an image. | |
112 * | |
113 * @attribute src | |
114 * @type string | |
115 * @default '' | |
116 */ | |
117 src: { | |
118 observer: '_srcChanged', | |
119 type: String, | |
120 value: '' | |
121 }, | |
122 | |
123 /** | |
124 * When true, the image is prevented from loading and any placeholder is | |
125 * shown. This may be useful when a binding to the src property is known
to | |
126 * be invalid, to prevent 404 requests. | |
127 * | |
128 * @attribute preventLoad | |
129 * @type boolean | |
130 * @default false | |
131 */ | |
132 preventLoad: { | |
133 type: Boolean, | |
134 value: false | |
135 }, | |
136 | |
137 /** | |
138 * Sets a sizing option for the image. Valid values are `contain` (full | |
139 * aspect ratio of the image is contained within the element and | |
140 * letterboxed) or `cover` (image is cropped in order to fully cover the | |
141 * bounds of the element), or `null` (default: image takes natural size). | |
142 * | |
143 * @attribute sizing | |
144 * @type string | |
145 * @default null | |
146 */ | |
147 sizing: { | |
148 type: String, | |
149 value: null | |
150 }, | |
151 | |
152 /** | |
153 * When a sizing option is uzed (`cover` or `contain`), this determines | |
154 * how the image is aligned within the element bounds. | |
155 * | |
156 * @attribute position | |
157 * @type string | |
158 * @default 'center' | |
159 */ | |
160 position: { | |
161 type: String, | |
162 value: 'center' | |
163 }, | |
164 | |
165 /** | |
166 * When `true`, any change to the `src` property will cause the `placehold
er` | |
167 * image to be shown until the | |
168 * | |
169 * @attribute preload | |
170 * @type boolean | |
171 * @default false | |
172 */ | |
173 preload: { | |
174 type: Boolean, | |
175 value: false | |
176 }, | |
177 | |
178 /** | |
179 * This image will be used as a background/placeholder until the src image
has | |
180 * loaded. Use of a data-URI for placeholder is encouraged for instant re
ndering. | |
181 * | |
182 * @attribute placeholder | |
183 * @type string | |
184 * @default null | |
185 */ | |
186 placeholder: { | |
187 type: String, | |
188 value: null | |
189 }, | |
190 | |
191 /** | |
192 * When `preload` is true, setting `fade` to true will cause the image to | |
193 * fade into place. | |
194 * | |
195 * @attribute fade | |
196 * @type boolean | |
197 * @default false | |
198 */ | |
199 fade: { | |
200 type: Boolean, | |
201 value: false | |
202 }, | |
203 | |
204 /** | |
205 * Read-only value that is true when the image is loaded. | |
206 * | |
207 * @attribute preloaded | |
208 * @type boolean | |
209 * @default false | |
210 */ | |
211 loaded: { | |
212 notify: true, | |
213 type: Boolean, | |
214 value: false | |
215 }, | |
216 | |
217 /** | |
218 * Read-only value that tracks the loading state of the image when the `pr
eload` | |
219 * option is used. | |
220 * | |
221 * @attribute loading | |
222 * @type boolean | |
223 * @default false | |
224 */ | |
225 loading: { | |
226 notify: true, | |
227 type: Boolean, | |
228 value: false | |
229 }, | |
230 | |
231 /** | |
232 * Can be used to set the width of image (e.g. via binding); size may also
be | |
233 * set via CSS. | |
234 * | |
235 * @attribute width | |
236 * @type number | |
237 * @default null | |
238 */ | |
239 width: { | |
240 observer: '_widthChanged', | |
241 type: Number, | |
242 value: null | |
243 }, | |
244 | |
245 /** | |
246 * Can be used to set the height of image (e.g. via binding); size may als
o be | |
247 * set via CSS. | |
248 * | |
249 * @attribute height | |
250 * @type number | |
251 * @default null | |
252 */ | |
253 height: { | |
254 observer: '_heightChanged', | |
255 type: Number, | |
256 value: null | |
257 }, | |
258 | |
259 _placeholderBackgroundUrl: { | |
260 type: String, | |
261 computed: '_computePlaceholderBackgroundUrl(preload,placeholder)', | |
262 observer: '_placeholderBackgroundUrlChanged' | |
263 }, | |
264 | |
265 requiresPreload: { | |
266 type: Boolean, | |
267 computed: '_computeRequiresPreload(preload,loaded)' | |
268 }, | |
269 | |
270 canLoad: { | |
271 type: Boolean, | |
272 computed: '_computeCanLoad(preventLoad, src)' | |
273 } | |
274 | |
275 }, | |
276 | |
277 observers: [ | |
278 '_transformChanged(sizing, position)', | |
279 '_loadBehaviorChanged(canLoad, preload, loaded)', | |
280 '_loadStateChanged(src, preload, loaded)', | |
281 ], | |
282 | |
283 ready: function() { | |
284 if (!this.hasAttribute('role')) { | |
285 this.setAttribute('role', 'img'); | |
286 } | |
287 }, | |
288 | |
289 _computeImageVisibility: function() { | |
290 return !!this.sizing; | |
291 }, | |
292 | |
293 _computePlaceholderVisibility: function() { | |
294 return !this.preload || (this.loaded && !this.fade); | |
295 }, | |
296 | |
297 _computePlaceholderClassName: function() { | |
298 if (!this.preload) { | |
299 return ''; | |
300 } | |
301 | |
302 var className = 'fit'; | |
303 if (this.loaded && this.fade) { | |
304 className += ' faded-out'; | |
305 } | |
306 return className; | |
307 }, | |
308 | |
309 _computePlaceholderBackgroundUrl: function() { | |
310 if (this.preload && this.placeholder) { | |
311 return 'url(' + this.placeholder + ')'; | |
312 } | |
313 | |
314 return null; | |
315 }, | |
316 | |
317 _computeRequiresPreload: function() { | |
318 return this.preload && !this.loaded; | |
319 }, | |
320 | |
321 _computeCanLoad: function() { | |
322 return Boolean(!this.preventLoad && this.src); | |
323 }, | |
324 | |
325 _widthChanged: function() { | |
326 this.style.width = isNaN(this.width) ? this.width : this.width + 'px'; | |
327 }, | |
328 | |
329 _heightChanged: function() { | |
330 this.style.height = isNaN(this.height) ? this.height : this.height + 'px'; | |
331 }, | |
332 | |
333 _srcChanged: function(newSrc, oldSrc) { | |
334 if (newSrc !== oldSrc) { | |
335 this.loaded = false; | |
336 } | |
337 }, | |
338 | |
339 _placeholderBackgroundUrlChanged: function() { | |
340 this.$.placeholder.style.backgroundImage = | |
341 this._placeholderBackgroundUrl; | |
342 }, | |
343 | |
344 _transformChanged: function() { | |
345 var placeholderStyle = this.$.placeholder.style; | |
346 | |
347 this.style.backgroundSize = | |
348 placeholderStyle.backgroundSize = this.sizing; | |
349 | |
350 this.style.backgroundPosition = | |
351 placeholderStyle.backgroundPosition = | |
352 this.sizing ? this.position : null; | |
353 | |
354 this.style.backgroundRepeat = | |
355 placeholderStyle.backgroundRepeat = | |
356 this.sizing ? 'no-repeat' : null; | |
357 }, | |
358 | |
359 _loadBehaviorChanged: function() { | |
360 var img; | |
361 | |
362 if (!this.canLoad) { | |
363 return; | |
364 } | |
365 | |
366 if (this.requiresPreload) { | |
367 img = new Image(); | |
368 img.src = this.src; | |
369 | |
370 this.loading = true; | |
371 | |
372 img.onload = function() { | |
373 this.loading = false; | |
374 this.loaded = true; | |
375 }.bind(this); | |
376 } else { | |
377 this.loaded = true; | |
378 } | |
379 }, | |
380 | |
381 _loadStateChanged: function() { | |
382 if (this.requiresPreload) { | |
383 return; | |
384 } | |
385 | |
386 if (this.sizing) { | |
387 this.style.backgroundImage = this.src ? 'url(' + this.src + ')': ''; | |
388 } else { | |
389 this.$.img.src = this.src || ''; | |
390 } | |
391 } | |
392 }); | |
393 | |
394 </script> | |
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