1 files changed, 53 insertions, 6 deletions

diff --git a/resources/src/jquery/jquery.hidpi.js b/resources/src/jquery/jquery.hidpi.js
index 8fca0567..aa6590bf 100644
--- a/resources/src/jquery/jquery.hidpi.js
+++ b/resources/src/jquery/jquery.hidpi.js
@@ -27,14 +27,15 @@
 $.devicePixelRatio = function () {
 	if ( window.devicePixelRatio !== undefined ) {
 		// Most web browsers:
-		// * WebKit (Safari, Chrome, Android browser, etc)
+		// * 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 doesn't report pixel ratio directly, but we can get the
+		// 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.
@@ -53,6 +54,52 @@ $.devicePixelRatio = function () {
 };
 
 /**
+ * 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
+ * @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.
  *
@@ -106,11 +153,11 @@ $.matchSrcSet = function ( devicePixelRatio, srcset ) {
 		selectedSrc = null;
 	candidates = srcset.split( / *, */ );
 	for ( i = 0; i < candidates.length; i++ ) {
-		candidate = candidates[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 );
+		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;