From 274afe0a5fa79ebe034ee412c44d20ccc9341bfb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Junod?= <frederic.junod@camptocamp.com>
Date: Thu, 27 Nov 2008 14:23:11 +0000
Subject: [PATCH] Keep the Util.alphaHack function result in a cache. r=pgiraud
 (closes #1825)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@8419 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf
---
 lib/OpenLayers/Util.js | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/lib/OpenLayers/Util.js b/lib/OpenLayers/Util.js
index db12e792a2..611ea839a8 100644
--- a/lib/OpenLayers/Util.js
+++ b/lib/OpenLayers/Util.js
@@ -390,6 +390,12 @@ OpenLayers.Util.onImageLoadError = function() {
     this.style.display = "";
 };
 
+/**
+ * Property: alphaHackNeeded
+ * {Boolean} true if the png alpha hack is necessary and possible, false otherwise.
+ */
+OpenLayers.Util.alphaHackNeeded = null;
+
 /**
  * Function: alphaHack
  * Checks whether it's necessary (and possible) to use the png alpha
@@ -397,25 +403,27 @@ OpenLayers.Util.onImageLoadError = function() {
  * Explorer.
  * 
  * Returns:
- * {Boolean} true if alpha has is necessary and possible, false otherwise.
+ * {Boolean} true if the png alpha hack is necessary and possible, false otherwise.
  */
 OpenLayers.Util.alphaHack = function() {
-    var arVersion = navigator.appVersion.split("MSIE");
-    var version = parseFloat(arVersion[1]);
-    var filter = false;
+    if (OpenLayers.Util.alphaHackNeeded == null) {
+        var arVersion = navigator.appVersion.split("MSIE");
+        var version = parseFloat(arVersion[1]);
+        var filter = false;
     
-    // IEs4Lin dies when trying to access document.body.filters, because 
-    // the property is there, but requires a DLL that can't be provided. This
-    // means that we need to wrap this in a try/catch so that this can
-    // continue.
+        // IEs4Lin dies when trying to access document.body.filters, because 
+        // the property is there, but requires a DLL that can't be provided. This
+        // means that we need to wrap this in a try/catch so that this can
+        // continue.
     
-    try { 
-        filter = !!(document.body.filters);
-    } catch (e) {
-    }    
+        try { 
+            filter = !!(document.body.filters);
+        } catch (e) {}    
     
-    return ( filter &&
-                      (version >= 5.5) && (version < 7) );
+        OpenLayers.Util.alphaHackNeeded = (filter && 
+                                           (version >= 5.5) && (version < 7));
+    }
+    return OpenLayers.Util.alphaHackNeeded;
 };
 
 /**