From b034e114d65066ad80c15a61d99f287ca45dfc75 Mon Sep 17 00:00:00 2001
From: Antoine Abt <antoine@abt.im>
Date: Wed, 20 Aug 2014 15:34:48 +0200
Subject: [PATCH] Restore opacity after drawing vector layers

---
 src/ol/renderer/canvas/canvasvectorlayerrenderer.js | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/ol/renderer/canvas/canvasvectorlayerrenderer.js b/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
index f54f5fbf6e..a3756b7609 100644
--- a/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
+++ b/src/ol/renderer/canvas/canvasvectorlayerrenderer.js
@@ -93,6 +93,10 @@ ol.renderer.canvas.VectorLayer.prototype.composeFrame =
     } else {
       replayContext = context;
     }
+    // for performance reasons, context.save / context.restore is not used
+    // to save and restore the transformation matrix and the opacity.
+    // see http://jsperf.com/context-save-restore-versus-variable
+    var alpha = replayContext.globalAlpha;
     replayContext.globalAlpha = layerState.opacity;
     replayGroup.replay(
         replayContext, frameState.extent, frameState.pixelRatio, transform,
@@ -102,6 +106,7 @@ ol.renderer.canvas.VectorLayer.prototype.composeFrame =
       this.dispatchRenderEvent(replayContext, frameState, transform);
       context.drawImage(replayContext.canvas, 0, 0);
     }
+    replayContext.globalAlpha = alpha;
   }
 
   this.dispatchPostComposeEvent(context, frameState, transform);