P5-1494: Fix for rulers jump to center

src/js/includes/RulerHandler.js

@@ -14,20 +14,24 @@ function RulerHandler(viewport) {
          * Triggers when handlebar is moved
          */
         onMove: function () {
-            var axis = this.axis;
+            updateRulerText(this);
-            var bounds = viewport.getBounds();
-            var pos = util.assertBetween(this[axis], bounds.min[axis], bounds.max[axis]);
-            this.marker[axis] = this[axis] = pos;
-            var dim = (this[axis] - bounds[axis]) / (viewport.getData().ppmm * 10 * viewport.canvas.getImage().scaleX);
-
-            if (axis === 'top') {
-                dim = viewport.getData().dim.height - dim;
-            }
-
-            this.setText(Math.round(dim * 100) / 100 + ' ' + viewport.getData().dim.units);
         }
     };
 
+    function updateRulerText(ruler) {
+        var axis = ruler.axis;
+        var bounds = viewport.getBounds();
+        var pos = util.assertBetween(ruler[axis], bounds.min[axis], bounds.max[axis]);
+        ruler.marker[axis] = ruler[axis] = pos;
+        var dim = (ruler[axis] - bounds[axis]) / (viewport.getData().ppmm * 10 * viewport.canvas.getImage().scaleX);
+
+        if (axis === 'top') {
+            dim = viewport.getData().dim.height - dim;
+        }
+
+        ruler.setText(Math.round(dim * 100) / 100 + ' ' + viewport.getData().dim.units);
+    }
+
     /**
      * @return {fabric.Line}
      */
@@ -62,16 +66,29 @@ function RulerHandler(viewport) {
      * @return {RulerHandler}
      */
     this.enable = function (enabled) {
+        var bounds = viewport.getBounds();
+
+        var keepPosition = (
+            enabled && (_enabled === enabled) &&
+            _lines.x && (Math.abs(_lines.x.width - bounds.width) < 1) &&
+            _lines.y && (Math.abs(_lines.y.height - bounds.height) < 1)
+        );
+
+        if (keepPosition) {
+            updateRulerText(_rect.x);
+            updateRulerText(_rect.y);
+            return this;
+        }
+
         _enabled = enabled;
+
         this.clear();
 
         if (!_enabled) {
             viewport.canvas.renderAll();
-            return;
+            return this;
         }
 
-        var bounds = viewport.getBounds();
-
         _lines = { x: getLine('x'), y: getLine('y') };
 
         viewport.canvas.add(_lines.x);