Add d3.pointers.

README.md

@@ -680,14 +680,24 @@ If *parameters* is a function, it is evaluated for each selected element, in ord
 
 <a name="pointer" href="#pointer">#</a> d3.<b>pointer</b>(<i>event</i>[, <i>target</i>]) · [Source](https://github.com/d3/d3-selection/blob/master/src/pointer.js)
 
-Returns a two-element array of numbers [*x*, *y*] representing the coordinates of the specified *event* relative to the specified *target*. If *target* is not specified, it defaults to *event*.currentTarget. (The *event* may also be a [touch](https://www.w3.org/TR/touch-events/#touch-interface).)
+Returns a two-element array of numbers [*x*, *y*] representing the coordinates of the specified *event* relative to the specified *target*. *event* can be a [UIEvent](https://developer.mozilla.org/en-US/docs/Web/API/UIEvent) (MouseEvent or TouchEvent), a [PointerEvent](https://developer.mozilla.org/en-US/docs/Web/API/PointerEvent), a custom event holding a UIEvent as *event*.sourceEvent, or a [touch](https://www.w3.org/TR/touch-events/#touch-interface).
+
+If *target* is not specified, it defaults to the source event’s currentTarget property, if available.
 
 If the *target* is an SVG element, the event’s coordinates are transformed using the [inverse](https://www.w3.org/TR/geometry-1/#dom-dommatrixreadonly-inverse) of the [screen coordinate transformation matrix](https://www.w3.org/TR/SVG/types.html#__svg__SVGGraphicsElement__getScreenCTM).
 
 If the *target* is an HTML element, the event’s coordinates are translated relative to the top-left corner of the *target*’s [bounding client rectangle](https://developer.mozilla.org/en-US/docs/Web/API/Element/getBoundingClientRect). (As such, the coordinate system can only be translated relative to the client coordinates. See also [GeometryUtils](https://www.w3.org/TR/cssom-view-1/#the-geometryutils-interface).)
 
 Otherwise, [*event*.pageX, *event*.pageY] is returned.
 
+In the case of touch events, the coordinates of the first touch are returned. To handle multitouch interactions, see [pointers](#pointers) instead.
+
+<a name="pointers" href="#pointers">#</a> d3.<b>pointers</b>(<i>event</i>[, <i>target</i>]) · [Source](https://github.com/d3/d3-selection/blob/master/src/pointers.js)
+
+Returns an array [[*x0*, *y0*], [*x1*, *y1*]…] of coordinates of the specified *event*’s pointer locations relative to the specified *target*. For mouse, stylus or single touch events, [*x0*, *y0*] is equivalent to d3.pointer(event, target). In the case of multi-touch events, the returned array contains a pair of coordinates for each of the touches.
+
+If *target* is not specified, it defaults to the source event’s currentTarget property, if available.
+
 ### Control Flow
 
 For advanced usage, selections provide methods for custom control flow.

src/index.js

@@ -5,6 +5,7 @@ export {default as matcher} from "./matcher.js";
 export {default as namespace} from "./namespace.js";
 export {default as namespaces} from "./namespaces.js";
 export {default as pointer} from "./pointer.js";
+export {default as pointers} from "./pointers.js";
 export {default as select} from "./select.js";
 export {default as selectAll} from "./selectAll.js";
 export {default as selection} from "./selection/index.js";

src/pointer.js

@@ -1,4 +1,8 @@
-export default function(event, node = event.currentTarget) {
+import sourceEvent from "./sourceEvent.js";
+
+export default function(event, node) {
+  event = sourceEvent(event);
+  if (node === undefined) node = event.currentTarget;
   if (node) {
     var svg = node.ownerSVGElement || node;
     if (svg.createSVGPoint) {

src/pointers.js

@@ -0,0 +1,11 @@
+import pointer from "./pointer.js";
+import sourceEvent from "./sourceEvent.js";
+
+export default function(events, node) {
+  if (events.target) { // i.e., instanceof Event, not TouchList or iterable
+    events = sourceEvent(events);
+    if (node === undefined) node = events.currentTarget;
+    events = events.touches || [events];
+  }
+  return Array.from(events, event => pointer(event, node));
+}

src/sourceEvent.js

@@ -0,0 +1,5 @@
+export default function(event) {
+  let sourceEvent;
+  while (sourceEvent = event.sourceEvent) event = sourceEvent;
+  return event;
+}