fix(menu): reposition menu if it would open off screen

Author: kara

src/lib/core/style/_menu-common.scss

@@ -47,43 +47,3 @@ $md-menu-side-padding: 16px !default;
     }
   }
 }
-
-/**
- * This mixin adds the correct panel transform styles based
- * on the direction that the menu panel opens.
- */
-@mixin md-menu-positions() {
-  &.md-menu-after.md-menu-below {
-    transform-origin: left top;
-  }
-
-  &.md-menu-after.md-menu-above {
-    transform-origin: left bottom;
-  }
-
-  &.md-menu-before.md-menu-below {
-    transform-origin: right top;
-  }
-
-  &.md-menu-before.md-menu-above {
-    transform-origin: right bottom;
-  }
-
-  [dir='rtl'] & {
-    &.md-menu-after.md-menu-below {
-      transform-origin: right top;
-    }
-
-    &.md-menu-after.md-menu-above {
-      transform-origin: right bottom;
-    }
-
-    &.md-menu-before.md-menu-below {
-      transform-origin: left top;
-    }
-
-    &.md-menu-before.md-menu-above {
-      transform-origin: left bottom;
-    }
-  }
-}

src/lib/menu/menu-directive.ts

@@ -41,6 +41,8 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
   /** Subscription to tab events on the menu panel */
   private _tabSubscription: Subscription;
 
+  selector = '.md-menu-panel';
+
   /** Config object to be passed into the menu's ngClass */
   _classList: any = {};
 
@@ -54,7 +56,6 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
               @Attribute('y-position') posY: MenuPositionY) {
     if (posX) { this._setPositionX(posX); }
     if (posY) { this._setPositionY(posY); }
-    this._setPositionClasses();
   }
 
   // TODO: internal
@@ -83,7 +84,6 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
       obj[className] = true;
       return obj;
     }, {});
-    this._setPositionClasses();
   }
 
   @Output() close = new EventEmitter<void>();
@@ -119,15 +119,4 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
     this.positionY = pos;
   }
 
-  /**
-   * It's necessary to set position-based classes to ensure the menu panel animation
-   * folds out from the correct direction.
-   */
-  private _setPositionClasses() {
-    this._classList['md-menu-before'] = this.positionX == 'before';
-    this._classList['md-menu-after'] = this.positionX == 'after';
-    this._classList['md-menu-above'] = this.positionY == 'above';
-    this._classList['md-menu-below'] = this.positionY == 'below';
-  }
-
 }

src/lib/menu/menu-panel.ts

@@ -4,6 +4,7 @@ import {MenuPositionX, MenuPositionY} from './menu-positions';
 export interface MdMenuPanel {
   positionX: MenuPositionX;
   positionY: MenuPositionY;
+  selector: string;
   templateRef: TemplateRef<any>;
   close: EventEmitter<void>;
   focusFirstItem: () => void;

src/lib/menu/menu-trigger.ts

@@ -22,7 +22,8 @@ import {
     TemplatePortal,
     ConnectedPositionStrategy,
     HorizontalConnectionPos,
-    VerticalConnectionPos
+    VerticalConnectionPos,
+    TransformOrigin
 } from '../core';
 import { Subscription } from 'rxjs/Subscription';
 
@@ -196,14 +197,33 @@ export class MdMenuTrigger implements AfterViewInit, OnDestroy {
    * @returns ConnectedPositionStrategy
    */
   private _getPosition(): ConnectedPositionStrategy  {
-    const positionX: HorizontalConnectionPos = this.menu.positionX === 'before' ? 'end' : 'start';
-    const positionY: VerticalConnectionPos = this.menu.positionY === 'above' ? 'bottom' : 'top';
-
-    return this._overlay.position().connectedTo(
-      this._element,
-      {originX: positionX, originY: positionY},
-      {overlayX: positionX, overlayY: positionY}
-    );
+    const [posX, fallbackX]: HorizontalConnectionPos[] =
+      this.menu.positionX === 'before' ? ['end', 'start'] : ['start', 'end'];
+
+    const [posY, fallbackY]: VerticalConnectionPos[] =
+      this.menu.positionY === 'above' ? ['bottom', 'top'] : ['top', 'bottom'];
+    return this._overlay.position()
+      .connectedTo(this._element,
+          {originX: posX, originY: posY}, {overlayX: posX, overlayY: posY})
+      .withTransformOrigin(this.menu.selector, this._transformOrigin(posX, posY))
+      .withFallbackPosition(
+          {originX: fallbackX, originY: posY},
+          {overlayX: fallbackX, overlayY: posY},
+          this._transformOrigin(fallbackX, posY))
+      .withFallbackPosition(
+          {originX: posX, originY: fallbackY},
+          {overlayX: posX, overlayY: fallbackY},
+          this._transformOrigin(posX, fallbackY))
+      .withFallbackPosition(
+          {originX: fallbackX, originY: fallbackY},
+          {overlayX: fallbackX, overlayY: fallbackY},
+          this._transformOrigin(fallbackX, fallbackY));
+  }
+
+  /** Converts the designated point into a TransformOrigin. */
+  private _transformOrigin(x: HorizontalConnectionPos,
+                           y: VerticalConnectionPos): TransformOrigin {
+    return `${x} ${y}` as TransformOrigin;
   }
 
   _handleMousedown(event: MouseEvent): void {

src/lib/menu/menu.scss

@@ -9,7 +9,6 @@ $md-menu-vertical-padding: 8px !default;
 
 .md-menu-panel {
   @include md-menu-base();
-  @include md-menu-positions();
 
   // max height must be 100% of the viewport height + one row height
   max-height: calc(100vh + 48px);