feat(overlay): allow for connected overlay to be positioned relative to a point

src/cdk/overlay/position/flexible-connected-position-strategy.spec.ts

@@ -700,6 +700,53 @@ describe('FlexibleConnectedPositionStrategy', () => {
 
     });
 
+    describe('with origin set to a point', () => {
+      it('should be able to render at the primary position', () => {
+        positionStrategy
+          .setOrigin({x: 50, y: 100})
+          .withPositions([{
+            originX: 'start',
+            originY: 'bottom',
+            overlayX: 'start',
+            overlayY: 'top'
+          }]);
+
+        attachOverlay({positionStrategy});
+
+        const overlayRect = overlayRef.overlayElement.getBoundingClientRect();
+        expect(Math.floor(overlayRect.top)).toBe(100);
+        expect(Math.floor(overlayRect.left)).toBe(50);
+      });
+
+      it('should be able to render at a fallback position', () => {
+        const viewportHeight = viewport.getViewportRect().height;
+
+        positionStrategy
+          .setOrigin({x: 50, y: viewportHeight})
+          .withPositions([
+              {
+                originX: 'start',
+                originY: 'bottom',
+                overlayX: 'start',
+                overlayY: 'top'
+              },
+              {
+                originX: 'start',
+                originY: 'top',
+                overlayX: 'start',
+                overlayY: 'bottom'
+              }
+          ]);
+
+        attachOverlay({positionStrategy});
+
+        const overlayRect = overlayRef.overlayElement.getBoundingClientRect();
+        expect(Math.floor(overlayRect.bottom)).toBe(viewportHeight);
+        expect(Math.floor(overlayRect.left)).toBe(50);
+      });
+
+    });
+
     it('should account for the `offsetX` pushing the overlay out of the screen', () => {
       // Position the element so it would have enough space to fit.
       originElement.style.top = '200px';

src/cdk/overlay/position/flexible-connected-position-strategy.ts

@@ -19,7 +19,7 @@ import {
 import {Observable, Subscription, Subject, Observer} from 'rxjs';
 import {OverlayReference} from '../overlay-reference';
 import {isElementScrolledOutsideView, isElementClippedByScrolling} from './scroll-clip';
-import {coerceCssPixelValue, coerceArray, coerceElement} from '@angular/cdk/coercion';
+import {coerceCssPixelValue, coerceArray} from '@angular/cdk/coercion';
 import {Platform} from '@angular/cdk/platform';
 import {OverlayContainer} from '../overlay-container';
 
@@ -29,6 +29,9 @@ import {OverlayContainer} from '../overlay-container';
 /** Class to be added to the overlay bounding box. */
 const boundingBoxClass = 'cdk-overlay-connected-position-bounding-box';
 
+/** Possible values that can be set as the origin of a FlexibleConnectedPositionStrategy. */
+export type FlexibleConnectedPositionStrategyOrigin = ElementRef | HTMLElement | Point;
+
 /**
  * A strategy for positioning overlays. Using this strategy, an overlay is given an
  * implicit position relative some origin element. The relative position is defined in terms of
@@ -80,7 +83,7 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
   _preferredPositions: ConnectionPositionPair[] = [];
 
   /** The origin element against which the overlay will be positioned. */
-  private _origin: HTMLElement;
+  private _origin: FlexibleConnectedPositionStrategyOrigin;
 
   /** The overlay pane element. */
   private _pane: HTMLElement;
@@ -139,7 +142,7 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
   }
 
   constructor(
-    connectedTo: ElementRef | HTMLElement,
+    connectedTo: FlexibleConnectedPositionStrategyOrigin,
     private _viewportRuler: ViewportRuler,
     private _document: Document,
     // @breaking-change 8.0.0 `_platform` and `_overlayContainer` parameters to be made required.
@@ -211,7 +214,7 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
     // the overlay relative to the origin.
     // We use the viewport rect to determine whether a position would go off-screen.
     this._viewportRect = this._getNarrowedViewportRect();
-    this._originRect = this._origin.getBoundingClientRect();
+    this._originRect = this._getOriginRect();
     this._overlayRect = this._pane.getBoundingClientRect();
 
     const originRect = this._originRect;
@@ -350,7 +353,7 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
    */
   reapplyLastPosition(): void {
     if (!this._isDisposed && (!this._platform || this._platform.isBrowser)) {
-      this._originRect = this._origin.getBoundingClientRect();
+      this._originRect = this._getOriginRect();
       this._overlayRect = this._pane.getBoundingClientRect();
       this._viewportRect = this._getNarrowedViewportRect();
 
@@ -427,11 +430,14 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
   }
 
   /**
-   * Sets the origin element, relative to which to position the overlay.
-   * @param origin Reference to the new origin element.
+   * Sets the origin, relative to which to position the overlay.
+   * Using an element origin is useful for building components that need to be positioned
+   * relatively to a trigger (e.g. dropdown menus or tooltips), whereas using a point can be
+   * used for cases like contextual menus which open relative to the user's pointer.
+   * @param origin Reference to the new origin.
    */
-  setOrigin(origin: ElementRef | HTMLElement): this {
-    this._origin = coerceElement(origin);
+  setOrigin(origin: FlexibleConnectedPositionStrategyOrigin): this {
+    this._origin = origin;
     return this;
   }
 
@@ -987,7 +993,7 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
    */
   private _getScrollVisibility(): ScrollingVisibility {
     // Note: needs fresh rects since the position could've changed.
-    const originBounds = this._origin.getBoundingClientRect();
+    const originBounds = this._getOriginRect();
     const overlayBounds =  this._pane.getBoundingClientRect();
 
     // TODO(jelbourn): instead of needing all of the client rects for these scrolling containers
@@ -1089,6 +1095,29 @@ export class FlexibleConnectedPositionStrategy implements PositionStrategy {
       this._appliedPanelClasses = [];
     }
   }
+
+  /** Returns the ClientRect of the current origin. */
+  private _getOriginRect(): ClientRect {
+    const origin = this._origin;
+
+    if (origin instanceof ElementRef) {
+      return origin.nativeElement.getBoundingClientRect();
+    }
+
+    if (origin instanceof HTMLElement) {
+      return origin.getBoundingClientRect();
+    }
+
+    // If the origin is a point, return a client rect as if it was a 0x0 element at the point.
+    return {
+      top: origin.y,
+      bottom: origin.y,
+      left: origin.x,
+      right: origin.x,
+      height: 0,
+      width: 0
+    };
+  }
 }
 
 /** A simple (x, y) coordinate. */

src/cdk/overlay/position/overlay-position-builder.ts

@@ -11,7 +11,10 @@ import {DOCUMENT} from '@angular/common';
 import {ElementRef, Inject, Injectable, Optional} from '@angular/core';
 import {OriginConnectionPosition, OverlayConnectionPosition} from './connected-position';
 import {ConnectedPositionStrategy} from './connected-position-strategy';
-import {FlexibleConnectedPositionStrategy} from './flexible-connected-position-strategy';
+import {
+  FlexibleConnectedPositionStrategy,
+  FlexibleConnectedPositionStrategyOrigin,
+} from './flexible-connected-position-strategy';
 import {GlobalPositionStrategy} from './global-position-strategy';
 import {Platform} from '@angular/cdk/platform';
 import {OverlayContainer} from '../overlay-container';
@@ -53,10 +56,11 @@ export class OverlayPositionBuilder {
 
   /**
    * Creates a flexible position strategy.
-   * @param elementRef
+   * @param origin Origin relative to which to position the overlay.
    */
-  flexibleConnectedTo(elementRef: ElementRef | HTMLElement): FlexibleConnectedPositionStrategy {
-    return new FlexibleConnectedPositionStrategy(elementRef, this._viewportRuler, this._document,
+  flexibleConnectedTo(origin: FlexibleConnectedPositionStrategyOrigin):
+    FlexibleConnectedPositionStrategy {
+    return new FlexibleConnectedPositionStrategy(origin, this._viewportRuler, this._document,
         this._platform, this._overlayContainer);
   }
 

tools/public_api_guard/cdk/overlay.d.ts

@@ -108,13 +108,13 @@ export declare class FlexibleConnectedPositionStrategy implements PositionStrate
     _preferredPositions: ConnectionPositionPair[];
     positionChanges: Observable<ConnectedOverlayPositionChange>;
     readonly positions: ConnectionPositionPair[];
-    constructor(connectedTo: ElementRef | HTMLElement, _viewportRuler: ViewportRuler, _document: Document, _platform?: Platform | undefined, _overlayContainer?: OverlayContainer | undefined);
+    constructor(connectedTo: FlexibleConnectedPositionStrategyOrigin, _viewportRuler: ViewportRuler, _document: Document, _platform?: Platform | undefined, _overlayContainer?: OverlayContainer | undefined);
     apply(): void;
     attach(overlayRef: OverlayReference): void;
     detach(): void;
     dispose(): void;
     reapplyLastPosition(): void;
-    setOrigin(origin: ElementRef | HTMLElement): this;
+    setOrigin(origin: FlexibleConnectedPositionStrategyOrigin): this;
     withDefaultOffsetX(offset: number): this;
     withDefaultOffsetY(offset: number): this;
     withFlexibleDimensions(flexibleDimensions?: boolean): this;
@@ -216,7 +216,7 @@ export declare class OverlayModule {
 export declare class OverlayPositionBuilder {
     constructor(_viewportRuler: ViewportRuler, _document: any, _platform?: Platform | undefined, _overlayContainer?: OverlayContainer | undefined);
     connectedTo(elementRef: ElementRef, originPos: OriginConnectionPosition, overlayPos: OverlayConnectionPosition): ConnectedPositionStrategy;
-    flexibleConnectedTo(elementRef: ElementRef | HTMLElement): FlexibleConnectedPositionStrategy;
+    flexibleConnectedTo(origin: FlexibleConnectedPositionStrategyOrigin): FlexibleConnectedPositionStrategy;
     global(): GlobalPositionStrategy;
 }