fix(tooltip): update placement on content change

Since the recompute of position is a heavy calculation and given
that this happens only when tooltip is visible, ie position
is already calculated, we can reuse it to update the position when
widht/height changes.

Closes angular-ui#96

Author: bekos

src/tooltip/tooltip.js

@@ -116,6 +116,7 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
           var triggers = getTriggers( undefined );
           var hasRegisteredTriggers = false;
           var hasEnableExp = angular.isDefined(attrs[prefix+'Enable']);
+          var position;
 
           // By default, the tooltip is not open.
           // TODO add ability to start tooltip opened
@@ -147,77 +148,74 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
             });
           }
 
-          // Show the tooltip popup element.
-          function show() {
-            var position,
-                ttWidth,
-                ttHeight,
+          // Calculate tootip's position
+          function updatePosition() {
+            var ttWidth = tooltip.prop( 'offsetWidth' ),
+                ttHeight = tooltip.prop( 'offsetHeight' ),
                 ttPosition;
-
-            // Don't show empty tooltips.
-            if ( ! scope.tt_content ) {
-              return;
-            }
-
-            // If there is a pending remove transition, we must cancel it, lest the
-            // tooltip be mysteriously removed.
-            if ( transitionTimeout ) {
-              $timeout.cancel( transitionTimeout );
-            }
-            
-            // Set the initial positioning.
-            tooltip.css({ top: 0, left: 0, display: 'block' });
-            
-            // Now we add it to the DOM because need some info about it. But it's not 
-            // visible yet anyway.
-            if ( appendToBody ) {
-                $document.find( 'body' ).append( tooltip );
-            } else {
-              element.after( tooltip );
-            }
-
-            // Get the position of the directive element.
-            position = appendToBody ? $position.offset( element ) : $position.position( element );
-
-            // Get the height and width of the tooltip so we can center it.
-            ttWidth = tooltip.prop( 'offsetWidth' );
-            ttHeight = tooltip.prop( 'offsetHeight' );
 
             // Calculate the tooltip's top and left coordinates to center it with
             // this directive.
             switch ( scope.tt_placement ) {
               case 'right':
                 ttPosition = {
-                  top: position.top + position.height / 2 - ttHeight / 2,
-                  left: position.left + position.width
+                  top: position.top + position.height / 2 - ttHeight / 2 + 'px',
+                  left: position.left + position.width + 'px'
                 };
                 break;
               case 'bottom':
                 ttPosition = {
-                  top: position.top + position.height,
-                  left: position.left + position.width / 2 - ttWidth / 2
+                  top: position.top + position.height + 'px',
+                  left: position.left + position.width / 2 - ttWidth / 2 + 'px'
                 };
                 break;
               case 'left':
                 ttPosition = {
-                  top: position.top + position.height / 2 - ttHeight / 2,
-                  left: position.left - ttWidth
+                  top: position.top + position.height / 2 - ttHeight / 2 + 'px',
+                  left: position.left - ttWidth + 'px'
                 };
                 break;
               default:
                 ttPosition = {
-                  top: position.top - ttHeight,
-                  left: position.left + position.width / 2 - ttWidth / 2
+                  top: position.top - ttHeight + 'px',
+                  left: position.left + position.width / 2 - ttWidth / 2 + 'px'
                 };
                 break;
             }
 
-            ttPosition.top += 'px';
-            ttPosition.left += 'px';
-
             // Now set the calculated positioning.
             tooltip.css( ttPosition );
-              
+          }
+          
+          // Show the tooltip popup element.
+          function show() {
+            // Don't show empty tooltips.
+            if ( ! scope.tt_content ) {
+              return;
+            }
+
+            // If there is a pending remove transition, we must cancel it, lest the
+            // tooltip be mysteriously removed.
+            if ( transitionTimeout ) {
+              $timeout.cancel( transitionTimeout );
+            }
+
+            tooltip.css({ display: 'block' });
+
+            // Now we add it to the DOM because need some info about it. But it's not 
+            // visible yet anyway.
+            if ( appendToBody ) {
+                $document.find( 'body' ).append( tooltip );
+            } else {
+              element.after( tooltip );
+            }
+
+            // Get the position of the directive element.
+            position = appendToBody ? $position.offset( element ) : $position.position( element );
+
+            // Place tooltip
+            updatePosition();
+
             // And show the tooltip.
             scope.tt_isOpen = true;
           }
@@ -248,8 +246,13 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
           attrs.$observe( type, function ( val ) {
             scope.tt_content = val;
 
-            if (!val && scope.tt_isOpen ) {
-              hide();
+            if (scope.tt_isOpen) {
+              if (!val) {
+                hide();
+              } else {
+                // Adjust based on the last known position of the directive element.
+                $timeout(updatePosition);
+              }
             }
           });