clearRect, not fill with transparent

Author: jpolitz

src/web/js/trove/world.js

@@ -532,8 +532,7 @@
               }
               var ctx = reusableCanvas.getContext("2d");
               ctx.save();
-              ctx.fillStyle = "rgba(255,255,255,0)";
-              ctx.fillRect(0, 0, width, height);
+              ctx.clearRect(0, 0, width, height);
               ctx.restore();
               theImage.render(ctx, 0, 0);
               success([toplevelNode, reusableCanvasNode]);