From 1119146486134753ceb58c9e627387d6e225cb9e Mon Sep 17 00:00:00 2001
From: Arjen Kopinga <kopinga@nieuwland.nl>
Date: Wed, 22 Feb 2012 15:39:31 +0100
Subject: [PATCH] Small fix for hit detection on a canvas layer as an illegal
 feature id might result at a location where the edge of one feature
 intersects the interior of another. This is due to antialiasing on the hit
 context canvas which can't be turned off, unfortunately.

---
 .gitignore                        |  2 ++
 examples/graphic-name.js          |  4 ++--
 lib/OpenLayers/Renderer/Canvas.js | 11 +++++++++--
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/.gitignore b/.gitignore
index 42b60260f3..0f81cf6d15 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,5 @@
 /doc/apidocs/
 /examples/example-list.js
 /examples/example-list.xml
+/examples/graphic-name.js
+/examples/graphic-name.html
diff --git a/examples/graphic-name.js b/examples/graphic-name.js
index 654a4c997d..267ae071dc 100644
--- a/examples/graphic-name.js
+++ b/examples/graphic-name.js
@@ -34,14 +34,14 @@ function init(){
     var styles = new OpenLayers.StyleMap({
         "default": {
             graphicName: "${type}",
-            pointRadius: 10,
+            pointRadius: 40,
             strokeColor: "fuchsia",
             strokeWidth: 2,
             fillColor: "lime",
             fillOpacity: 0.6
         },
         "select": {
-            pointRadius: 20,
+            pointRadius: 50,
             fillOpacity: 1,
             rotation: 45
         }
diff --git a/lib/OpenLayers/Renderer/Canvas.js b/lib/OpenLayers/Renderer/Canvas.js
index da82e1d7f9..e180ef7288 100644
--- a/lib/OpenLayers/Renderer/Canvas.js
+++ b/lib/OpenLayers/Renderer/Canvas.js
@@ -786,7 +786,7 @@ OpenLayers.Renderer.Canvas = OpenLayers.Class(OpenLayers.Renderer, {
      *     layer.
      */
     getFeatureIdFromEvent: function(evt) {
-        var feature;
+        var featureId, feature;
         if (this.hitDetection) {
             // this dragging check should go in the feature handler
             if (!this.map.dragging) {
@@ -797,7 +797,14 @@ OpenLayers.Renderer.Canvas = OpenLayers.Class(OpenLayers.Renderer, {
                 if (data[3] === 255) { // antialiased
                     var id = data[2] + (256 * (data[1] + (256 * data[0])));
                     if (id) {
-                        feature = this.features["OpenLayers.Feature.Vector_" + (id - 1 + this.hitOverflow)][0];
+                        featureId = "OpenLayers.Feature.Vector_" + (id - 1 + this.hitOverflow);
+                        try {
+                            feature = this.features["OpenLayers.Feature.Vector_" + (id - 1 + this.hitOverflow)][0];
+                        } catch(err) {
+                            // Because of antialiasing on the canvas, when the hit location is at a point where the edge of
+                            // one symbol intersects the interior of another symbol, a wrong hit color (and therefore id) results.
+                            // todo: set Antialiasing = 'off' on the hitContext as soon as browsers allow it.
+                        }
                     }
                 }
             }