Address comments.

CHANGELOG.rst

@@ -5,6 +5,8 @@ These are notable changes in edx-platform.  This is a rolling list of changes,
 in roughly chronological order, most recent first.  Add your entries at or near
 the top.  Include a label indicating the component affected.
 
+Blades: Fix bug when Image mapping problems are not working for students in IE. BLD-413.
+
 Blades: Add template that displays the most up-to-date features of
 drag-and-drop. BLD-479.
 

common/lib/xmodule/xmodule/js/src/capa/imageinput.js

@@ -4,19 +4,24 @@
 //
 ////////////////////////////////////////////////////////////////////////////////
 
-// click on image, return coordinates
-// put a dot at location of click, on imag
+// click on image, update coordinates
+// put a dot at location of click, on image
 
-window.image_input_click = function(id,event){
-    iidiv = document.getElementById("imageinput_"+id);
-    pos_x = event.offsetX?(event.offsetX):event.pageX-iidiv.offsetLeft;
-    pos_y = event.offsetY?(event.offsetY):event.pageY-iidiv.offsetTop;
-    result = "[" + Math.round(pos_x) + "," + Math.round(pos_y) + "]";
-    cx = (pos_x-15) +"px";
-    cy = (pos_y-15)  +"px";
+window.image_input_click = function (id, event) {
+    var iidiv = document.getElementById("imageinput_" + id),
+        pos_x = event.offsetX ? (event.offsetX) : event.pageX - iidiv.offsetLeft,
+        pos_y = event.offsetY ? (event.offsetY) : event.pageY - iidiv.offsetTop,
+        // To reduce differences between values returned by different kinds of
+        // browsers, we round `pos_x` and `pos_y`.
+        // IE10: `pos_x` and `pos_y` - float.
+        // Chrome, FF: `pos_x` and `pos_y` - integers.
+        result = "[" + Math.round(pos_x) + "," + Math.round(pos_y) + "]",
+        cx = (pos_x - 15) + "px",
+        cy = (pos_y - 15) + "px",
+        cross = document.getElementById("cross_" + id);
 
-    document.getElementById("cross_"+id).style.left = cx;
-    document.getElementById("cross_"+id).style.top = cy;
-    document.getElementById("cross_"+id).style.visibility = "visible" ;
-    document.getElementById("input_"+id).value =result;
+    cross.style.left = cx;
+    cross.style.top = cy;
+    cross.style.visibility = "visible" ;
+    document.getElementById("input_" + id).value = result;
 };