refactor addLabelData function - add rotateXY function

Author: archmoj

src/traces/contour/plot.js

@@ -553,16 +553,19 @@ exports.addLabelData = function(loc, textOpts, labelData, labelClipPathData) {
 
     var sin = Math.sin(theta);
     var cos = Math.cos(theta);
-    var dxw = cos * w / 2;
-    var dxh = sin * h / 2;
-    var dyw = sin * w / 2;
-    var dyh = -cos * h / 2;
+
+    var rotateXY = function(dx, dy) {
+        return [
+            x + dx * cos - dy * sin,
+            y + dx * sin + dy * cos
+        ];
+    };
 
     var bBoxPts = [
-        [x - dxw - dxh, y - dyw - dyh],
-        [x + dxw - dxh, y + dyw - dyh],
-        [x + dxw + dxh, y + dyw + dyh],
-        [x - dxw + dxh, y - dyw + dyh],
+        rotateXY(-w / 2, -h / 2),
+        rotateXY(-w / 2, h / 2),
+        rotateXY(w / 2, h / 2),
+        rotateXY(w / 2, -h / 2)
     ];
 
     labelData.push({