iron-image.html
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<!--
@license
Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->
<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="../iron-flex-layout/iron-flex-layout.html">
<!--
`iron-image` is an element for displaying an image that provides useful sizing and
preloading options not found on the standard `<img>` tag.
The `sizing` option allows the image to be either cropped (`cover`) or
letterboxed (`contain`) to fill a fixed user-size placed on the element.
The `preload` option prevents the browser from rendering the image until the
image is fully loaded. In the interim, either the element's CSS `background-color`
can be be used as the placeholder, or the `placeholder` property can be
set to a URL (preferably a data-URI, for instant rendering) for an
placeholder image.
The `fade` option (only valid when `preload` is set) will cause the placeholder
image/color to be faded out once the image is rendered.
Examples:
Basically identical to `<img src="...">` tag:
<iron-image src="http://lorempixel.com/400/400"></iron-image>
Will letterbox the image to fit:
<iron-image style="width:400px; height:400px;" sizing="contain"
src="http://lorempixel.com/600/400"></iron-image>
Will crop the image to fit:
<iron-image style="width:400px; height:400px;" sizing="cover"
src="http://lorempixel.com/600/400"></iron-image>
Will show light-gray background until the image loads:
<iron-image style="width:400px; height:400px; background-color: lightgray;"
sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image>
Will show a base-64 encoded placeholder image until the image loads:
<iron-image style="width:400px; height:400px;" placeholder="data:image/gif;base64,..."
sizing="cover" preload src="http://lorempixel.com/600/400"></iron-image>
Will fade the light-gray background out once the image is loaded:
<iron-image style="width:400px; height:400px; background-color: lightgray;"
sizing="cover" preload fade src="http://lorempixel.com/600/400"></iron-image>
Custom property | Description | Default
----------------|-------------|----------
`--iron-image-placeholder` | Mixin applied to #placeholder | `{}`
`--iron-image-width` | Sets the width of the wrapped image | `auto`
`--iron-image-height` | Sets the height of the wrapped image | `auto`
@group Iron Elements
@element iron-image
@demo demo/index.html
-->
<dom-module id="iron-image">
<template>
<style>
:host {
display: inline-block;
overflow: hidden;
position: relative;
}
#sizedImgDiv {
@apply(--layout-fit);
display: none;
}
#img {
display: block;
width: var(--iron-image-width, auto);
height: var(--iron-image-height, auto);
}
:host([sizing]) #sizedImgDiv {
display: block;
}
:host([sizing]) #img {
display: none;
}
#placeholder {
@apply(--layout-fit);
background-color: inherit;
opacity: 1;
@apply(--iron-image-placeholder);
}
#placeholder.faded-out {
transition: opacity 0.5s linear;
opacity: 0;
}
</style>
<div id="sizedImgDiv"
role="img"
hidden$="[[_computeImgDivHidden(sizing)]]"
aria-hidden$="[[_computeImgDivARIAHidden(alt)]]"
aria-label$="[[_computeImgDivARIALabel(alt, src)]]"></div>
<img id="img" alt$="[[alt]]" hidden$="[[_computeImgHidden(sizing)]]">
<div id="placeholder"
hidden$="[[_computePlaceholderHidden(preload, fade, loading, loaded)]]"
class$="[[_computePlaceholderClassName(preload, fade, loading, loaded)]]"></div>
</template>
<script>
Polymer({
is: 'iron-image',
properties: {
/**
* The URL of an image.
*/
src: {
observer: '_srcChanged',
type: String,
value: ''
},
/**
* A short text alternative for the image.
*/
alt: {
type: String,
value: null
},
/**
* When true, the image is prevented from loading and any placeholder is
* shown. This may be useful when a binding to the src property is known to
* be invalid, to prevent 404 requests.
*/
preventLoad: {
type: Boolean,
value: false,
observer: '_preventLoadChanged'
},
/**
* Sets a sizing option for the image. Valid values are `contain` (full
* aspect ratio of the image is contained within the element and
* letterboxed) or `cover` (image is cropped in order to fully cover the
* bounds of the element), or `null` (default: image takes natural size).
*/
sizing: {
type: String,
value: null,
reflectToAttribute: true
},
/**
* When a sizing option is used (`cover` or `contain`), this determines
* how the image is aligned within the element bounds.
*/
position: {
type: String,
value: 'center'
},
/**
* When `true`, any change to the `src` property will cause the `placeholder`
* image to be shown until the new image has loaded.
*/
preload: {
type: Boolean,
value: false
},
/**
* This image will be used as a background/placeholder until the src image has
* loaded. Use of a data-URI for placeholder is encouraged for instant rendering.
*/
placeholder: {
type: String,
value: null,
observer: '_placeholderChanged'
},
/**
* When `preload` is true, setting `fade` to true will cause the image to
* fade into place.
*/
fade: {
type: Boolean,
value: false
},
/**
* Read-only value that is true when the image is loaded.
*/
loaded: {
notify: true,
readOnly: true,
type: Boolean,
value: false
},
/**
* Read-only value that tracks the loading state of the image when the `preload`
* option is used.
*/
loading: {
notify: true,
readOnly: true,
type: Boolean,
value: false
},
/**
* Read-only value that indicates that the last set `src` failed to load.
*/
error: {
notify: true,
readOnly: true,
type: Boolean,
value: false
},
/**
* Can be used to set the width of image (e.g. via binding); size may also be
* set via CSS.
*/
width: {
observer: '_widthChanged',
type: Number,
value: null
},
/**
* Can be used to set the height of image (e.g. via binding); size may also be
* set via CSS.
*
* @attribute height
* @type number
* @default null
*/
height: {
observer: '_heightChanged',
type: Number,
value: null
},
},
observers: [
'_transformChanged(sizing, position)'
],
ready: function() {
var img = this.$.img;
img.onload = function() {
if (this.$.img.src !== this._resolveSrc(this.src)) return;
this._setLoading(false);
this._setLoaded(true);
this._setError(false);
}.bind(this);
img.onerror = function() {
if (this.$.img.src !== this._resolveSrc(this.src)) return;
this._reset();
this._setLoading(false);
this._setLoaded(false);
this._setError(true);
}.bind(this);
this._resolvedSrc = '';
},
_load: function(src) {
if (src) {
this.$.img.src = src;
} else {
this.$.img.removeAttribute('src');
}
this.$.sizedImgDiv.style.backgroundImage = src ? 'url("' + src + '")' : '';
this._setLoading(true);
this._setLoaded(false);
this._setError(false);
},
_reset: function() {
this.$.img.removeAttribute('src');
this.$.sizedImgDiv.style.backgroundImage = '';
this._setLoading(false);
this._setLoaded(false);
this._setError(false);
},
_computePlaceholderHidden: function() {
return !this.preload || (!this.fade && !this.loading && this.loaded);
},
_computePlaceholderClassName: function() {
return (this.preload && this.fade && !this.loading && this.loaded) ? 'faded-out' : '';
},
_computeImgDivHidden: function() {
return !this.sizing;
},
_computeImgDivARIAHidden: function() {
return this.alt === '' ? 'true' : undefined;
},
_computeImgDivARIALabel: function() {
if (this.alt !== null) {
return this.alt;
}
// Polymer.ResolveUrl.resolveUrl will resolve '' relative to a URL x to
// that URL x, but '' is the default for src.
if (this.src === '') {
return '';
}
var pathComponents = (new URL(this._resolveSrc(this.src))).pathname.split("/");
return pathComponents[pathComponents.length - 1];
},
_computeImgHidden: function() {
return !!this.sizing;
},
_widthChanged: function() {
this.style.width = isNaN(this.width) ? this.width : this.width + 'px';
},
_heightChanged: function() {
this.style.height = isNaN(this.height) ? this.height : this.height + 'px';
},
_preventLoadChanged: function() {
if (this.preventLoad || this.loaded) return;
this._reset();
this._load(this.src);
},
_srcChanged: function(newSrc, oldSrc) {
var newResolvedSrc = this._resolveSrc(newSrc);
if (newResolvedSrc === this._resolvedSrc) return;
this._resolvedSrc = newResolvedSrc;
this._reset();
if (!this.preventLoad) {
this._load(newSrc);
}
},
_placeholderChanged: function() {
this.$.placeholder.style.backgroundImage =
this.placeholder ? 'url("' + this.placeholder + '")' : '';
},
_transformChanged: function() {
var sizedImgDivStyle = this.$.sizedImgDiv.style;
var placeholderStyle = this.$.placeholder.style;
sizedImgDivStyle.backgroundSize =
placeholderStyle.backgroundSize =
this.sizing;
sizedImgDivStyle.backgroundPosition =
placeholderStyle.backgroundPosition =
this.sizing ? this.position : '';
sizedImgDivStyle.backgroundRepeat =
placeholderStyle.backgroundRepeat =
this.sizing ? 'no-repeat' : '';
},
_resolveSrc: function(testSrc) {
return Polymer.ResolveUrl.resolveUrl(testSrc, this.ownerDocument.baseURI);
}
});
</script>
</dom-module>