From bd615fb19f0dfa258ef57d208c222570b3998cc5 Mon Sep 17 00:00:00 2001
From: Tom MacWright <tom@macwright.org>
Date: Fri, 8 Feb 2013 10:48:00 -0500
Subject: [PATCH] Cache mousePosition

---
 js/id/svg/labels.js | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/js/id/svg/labels.js b/js/id/svg/labels.js
index 5c817a712..883147d3e 100644
--- a/js/id/svg/labels.js
+++ b/js/id/svg/labels.js
@@ -225,11 +225,14 @@ iD.svg.Labels = function(projection) {
 
     var rtree = new RTree(),
         rectangles = {},
-        mousePosition;
+        mousePosition, cacheDimensions;
 
     return function drawLabels(surface, graph, entities, filter, dimensions, fullRedraw) {
 
-        mousePosition = iD.util.fastMouse(surface.node().parentNode);
+        if (!mousePosition || dimensions.join(',') !== cacheDimensions) {
+            mousePosition = iD.util.fastMouse(surface.node().parentNode);
+            cacheDimensions = dimensions.join(',');
+        }
 
         d3.select(surface.node().parentNode)
             .on('mousemove.hidelabels', hideOnMouseover);