--- /dev/null
+/**
+ * Responsive images based on `srcset` and `window.devicePixelRatio` emulation where needed.
+ *
+ * Call `.hidpi()` on a document or part of a document to proces image srcsets within that section.
+ *
+ * `$.devicePixelRatio()` can be used as a substitute for `window.devicePixelRatio`.
+ * It provides a familiar interface to retrieve the pixel ratio for browsers that don't
+ * implement `window.devicePixelRatio` but do have a different way of getting it.
+ *
+ * @class jQuery.plugin.hidpi
+ */
+( function ( $ ) {
+
+ /**
+ * Get reported or approximate device pixel ratio.
+ *
+ * - 1.0 means 1 CSS pixel is 1 hardware pixel
+ * - 2.0 means 1 CSS pixel is 2 hardware pixels
+ * - etc.
+ *
+ * Uses `window.devicePixelRatio` if available, or CSS media queries on IE.
+ *
+ * @static
+ * @inheritable
+ * @return {number} Device pixel ratio
+ */
+ $.devicePixelRatio = function () {
+ if ( window.devicePixelRatio !== undefined ) {
+ // Most web browsers:
+ // * WebKit/Blink (Safari, Chrome, Android browser, etc)
+ // * Opera
+ // * Firefox 18+
+ // * Microsoft Edge (Windows 10)
+ return window.devicePixelRatio;
+ } else if ( window.msMatchMedia !== undefined ) {
+ // Windows 8 desktops / tablets, probably Windows Phone 8
+ //
+ // IE 10/11 doesn't report pixel ratio directly, but we can get the
+ // screen DPI and divide by 96. We'll bracket to [1, 1.5, 2.0] for
+ // simplicity, but you may get different values depending on zoom
+ // factor, size of screen and orientation in Metro IE.
+ if ( window.msMatchMedia( '(min-resolution: 192dpi)' ).matches ) {
+ return 2;
+ } else if ( window.msMatchMedia( '(min-resolution: 144dpi)' ).matches ) {
+ return 1.5;
+ } else {
+ return 1;
+ }
+ } else {
+ // Legacy browsers...
+ // Assume 1 if unknown.
+ return 1;
+ }
+ };
+
+ /**
+ * Bracket a given device pixel ratio to one of [1, 1.5, 2].
+ *
+ * This is useful for grabbing images on the fly with sizes based on the display
+ * density, without causing slowdown and extra thumbnail renderings on devices
+ * that are slightly different from the most common sizes.
+ *
+ * The bracketed ratios match the default 'srcset' output on MediaWiki thumbnails,
+ * so will be consistent with default renderings.
+ *
+ * @static
+ * @inheritable
+ * @param {number} baseRatio Base ratio
+ * @return {number} Device pixel ratio
+ */
+ $.bracketDevicePixelRatio = function ( baseRatio ) {
+ if ( baseRatio > 1.5 ) {
+ return 2;
+ } else if ( baseRatio > 1 ) {
+ return 1.5;
+ } else {
+ return 1;
+ }
+ };
+
+ /**
+ * Get reported or approximate device pixel ratio, bracketed to [1, 1.5, 2].
+ *
+ * This is useful for grabbing images on the fly with sizes based on the display
+ * density, without causing slowdown and extra thumbnail renderings on devices
+ * that are slightly different from the most common sizes.
+ *
+ * The bracketed ratios match the default 'srcset' output on MediaWiki thumbnails,
+ * so will be consistent with default renderings.
+ *
+ * - 1.0 means 1 CSS pixel is 1 hardware pixel
+ * - 1.5 means 1 CSS pixel is 1.5 hardware pixels
+ * - 2.0 means 1 CSS pixel is 2 hardware pixels
+ *
+ * @static
+ * @inheritable
+ * @return {number} Device pixel ratio
+ */
+ $.bracketedDevicePixelRatio = function () {
+ return $.bracketDevicePixelRatio( $.devicePixelRatio() );
+ };
+
+ /**
+ * Implement responsive images based on srcset attributes, if browser has no
+ * native srcset support.
+ *
+ * @return {jQuery} This selection
+ * @chainable
+ */
+ $.fn.hidpi = function () {
+ var $target = this,
+ // TODO add support for dpi media query checks on Firefox, IE
+ devicePixelRatio = $.devicePixelRatio(),
+ testImage = new Image();
+
+ if ( devicePixelRatio > 1 && testImage.srcset === undefined ) {
+ // No native srcset support.
+ $target.find( 'img' ).each( function () {
+ var $img = $( this ),
+ srcset = $img.attr( 'srcset' ),
+ match;
+ if ( typeof srcset === 'string' && srcset !== '' ) {
+ match = $.matchSrcSet( devicePixelRatio, srcset );
+ if ( match !== null ) {
+ $img.attr( 'src', match );
+ }
+ }
+ } );
+ }
+
+ return $target;
+ };
+
+ /**
+ * Match a srcset entry for the given device pixel ratio
+ *
+ * Exposed for testing.
+ *
+ * @private
+ * @static
+ * @param {number} devicePixelRatio
+ * @param {string} srcset
+ * @return {Mixed} null or the matching src string
+ */
+ $.matchSrcSet = function ( devicePixelRatio, srcset ) {
+ var candidates,
+ candidate,
+ bits,
+ src,
+ i,
+ ratioStr,
+ ratio,
+ selectedRatio = 1,
+ selectedSrc = null;
+ candidates = srcset.split( / *, */ );
+ for ( i = 0; i < candidates.length; i++ ) {
+ candidate = candidates[ i ];
+ bits = candidate.split( / +/ );
+ src = bits[ 0 ];
+ if ( bits.length > 1 && bits[ 1 ].charAt( bits[ 1 ].length - 1 ) === 'x' ) {
+ ratioStr = bits[ 1 ].slice( 0, -1 );
+ ratio = parseFloat( ratioStr );
+ if ( ratio <= devicePixelRatio && ratio > selectedRatio ) {
+ selectedRatio = ratio;
+ selectedSrc = src;
+ }
+ }
+ }
+ return selectedSrc;
+ };
+
+ /**
+ * @class jQuery
+ * @mixins jQuery.plugin.hidpi
+ */
+
+}( jQuery ) );
scripts.mit.edu / autoinstallsdev / mediawiki.git / blobdiff