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Small refactor to relative_mouse_coords: now the functionality which
returns an element's absolute position on the web page is split out
into a subfunction that can be called directly.

[originally from svn r9819]

--- a/emccpre.js

+++ b/emccpre.js

@@ -103,13 +103,11 @@

 // The undo and redo buttons. Used by js_enable_undo_redo().

 var undo_button, redo_button;

-// Helper function which is passed a mouse event object and a DOM

-// element, and returns the coordinates of the mouse event relative to

-// the top left corner of the element by iterating upwards through the

-// DOM finding each element's offset from its parent, and thus

-// calculating the page-relative position of the target element so

-// that we can subtract that from event.page{X,Y}.

-function relative_mouse_coords(event, element) {

+// Helper function to find the absolute position of a given DOM

+// element on a page, by iterating upwards through the DOM finding

+// each element's offset from its parent, and thus calculating the

+// page-relative position of the target element.

+function element_coords(element) {

     var ex = 0, ey = 0;

     while (element.offsetParent) {

         ex += element.offsetLeft;

@@ -116,8 +114,17 @@

         ey += element.offsetTop;

         element = element.offsetParent;

     }

-    return {x: event.pageX - ex,

-            y: event.pageY - ey};

+    return {x: ex, y:ey};

+}

+

+// Helper function which is passed a mouse event object and a DOM

+// element, and returns the coordinates of the mouse event relative to

+// the top left corner of the element by subtracting element_coords

+// from event.page{X,Y}.

+function relative_mouse_coords(event, element) {

+    var ecoords = element_coords(element);

+    return {x: event.pageX - ecoords.x,

+            y: event.pageY - ecoords.y};

 }

 // Init function called from body.onload.