feat(ripple): support multi-touch (#12643)

Currently when using multi-touch on a ripple trigger, the ripple will keep firing from the first touch position (e.g. putting one finger down and then tapping with another). These changes will fire off a ripple for each individual touch.

src/cdk/testing/event-objects.ts

@@ -42,7 +42,8 @@ export function createTouchEvent(type: string, pageX = 0, pageY = 0) {
   // the touch details.
   Object.defineProperties(event, {
     touches: {value: [touchDetails]},
-    targetTouches: {value: [touchDetails]}
+    targetTouches: {value: [touchDetails]},
+    changedTouches: {value: [touchDetails]}
   });
 
   return event;

src/lib/core/ripple/ripple-renderer.ts

@@ -264,8 +264,13 @@ export class RippleRenderer {
       this._lastTouchStartEvent = Date.now();
       this._isPointerDown = true;
 
-      this.fadeInRipple(
-          event.touches[0].clientX, event.touches[0].clientY, this._target.rippleConfig);
+      // Use `changedTouches` so we skip any touches where the user put
+      // their finger down, but used another finger to tap the element again.
+      const touches = event.changedTouches;
+
+      for (let i = 0; i < touches.length; i++) {
+        this.fadeInRipple(touches[i].clientX, touches[i].clientY, this._target.rippleConfig);
+      }
     }
   }
 

src/lib/core/ripple/ripple.spec.ts

@@ -1,7 +1,12 @@
 import {TestBed, ComponentFixture, fakeAsync, tick, inject} from '@angular/core/testing';
 import {Component, ViewChild} from '@angular/core';
 import {Platform} from '@angular/cdk/platform';
-import {dispatchMouseEvent, dispatchTouchEvent} from '@angular/cdk/testing';
+import {
+  dispatchEvent,
+  createTouchEvent,
+  dispatchMouseEvent,
+  dispatchTouchEvent,
+} from '@angular/cdk/testing';
 import {defaultRippleAnimationConfig, RippleAnimationConfig} from './ripple-renderer';
 import {
   MatRipple, MatRippleModule, MAT_RIPPLE_GLOBAL_OPTIONS, RippleState, RippleGlobalOptions
@@ -121,6 +126,32 @@ describe('MatRipple', () => {
       expect(rippleTarget.querySelectorAll('.mat-ripple-element').length).toBe(0);
     }));
 
+    it('should launch multiple ripples for multi-touch', fakeAsync(() => {
+      const touchEvent = createTouchEvent('touchstart');
+
+      Object.defineProperties(touchEvent, {
+        changedTouches: {
+          value: [
+            {pageX: 0, pageY: 0},
+            {pageX: 10, pageY: 10},
+            {pageX: 20, pageY: 20}
+          ]
+        }
+      });
+
+      dispatchEvent(rippleTarget, touchEvent);
+      expect(rippleTarget.querySelectorAll('.mat-ripple-element').length).toBe(3);
+
+      tick(enterDuration);
+      expect(rippleTarget.querySelectorAll('.mat-ripple-element').length).toBe(3);
+
+      dispatchTouchEvent(rippleTarget, 'touchend');
+
+      tick(exitDuration);
+
+      expect(rippleTarget.querySelectorAll('.mat-ripple-element').length).toBe(0);
+    }));
+
     it('should ignore synthetic mouse events after touchstart', () => fakeAsync(() => {
       dispatchTouchEvent(rippleTarget, 'touchstart');
       dispatchTouchEvent(rippleTarget, 'mousedown');

src/material-examples/ripple-overview/ripple-overview-example.css

@@ -5,6 +5,8 @@
   width: 300px;
   height: 300px;
   line-height: 300px;
+  -webkit-user-drag: none;
+  -webkit-tap-highlight-color: transparent;
 }
 
 /** Styles to make the demo look better. */