Clarify which functions expect (event, …) and which expect (selection…

…, …); and repair the calls that were mixed-up.

*event-based functions:*
- Gesture (hence event = this.args[0])
- filter
- wheelDelta

*selection-based functions:*
- extent
- transform
- schedule
- k,p (in scaleBy & scaleTo)
- x,y (in translateBy)

In addition, an event that triggers a transition (such as a zoom.dblclick) can be persisted throughout the transition as the zoomEvent.sourceEvent (fixes d3#202).

src/zoom.js

@@ -80,11 +80,11 @@ export default function() {
         .style("-webkit-tap-highlight-color", "rgba(0,0,0,0)");
   }
 
-  zoom.transform = function(collection, transform, point) {
+  zoom.transform = function(collection, transform, point, event) {
     var selection = collection.selection ? collection.selection() : collection;
     selection.property("__zoom", defaultTransform);
     if (collection !== selection) {
-      schedule(collection, transform, point);
+      schedule(collection, transform, point, event);
     } else {
       selection.interrupt().each(function() {
         gesture(this, [null, ...arguments])
@@ -95,35 +95,35 @@ export default function() {
     }
   };
 
-  zoom.scaleBy = function(selection, k, p) {
+  zoom.scaleBy = function(selection, k, p, event) {
     zoom.scaleTo(selection, function() {
       var k0 = this.__zoom.k,
           k1 = typeof k === "function" ? k.apply(this, arguments) : k;
       return k0 * k1;
-    }, p);
+    }, p, event);
   };
 
-  zoom.scaleTo = function(selection, k, p) {
+  zoom.scaleTo = function(selection, k, p, event) {
     zoom.transform(selection, function() {
       var e = extent.apply(this, arguments),
           t0 = this.__zoom,
           p0 = p == null ? centroid(e) : typeof p === "function" ? p.apply(this, arguments) : p,
           p1 = t0.invert(p0),
           k1 = typeof k === "function" ? k.apply(this, arguments) : k;
       return constrain(translate(scale(t0, k1), p0, p1), e, translateExtent);
-    }, p);
+    }, p, event);
   };
 
-  zoom.translateBy = function(selection, x, y) {
+  zoom.translateBy = function(selection, x, y, event) {
     zoom.transform(selection, function() {
       return constrain(this.__zoom.translate(
         typeof x === "function" ? x.apply(this, arguments) : x,
         typeof y === "function" ? y.apply(this, arguments) : y
       ), extent.apply(this, arguments), translateExtent);
-    });
+    }, null, event);
   };
 
-  zoom.translateTo = function(selection, x, y, p) {
+  zoom.translateTo = function(selection, x, y, p, event) {
     zoom.transform(selection, function() {
       var e = extent.apply(this, arguments),
           t = this.__zoom,
@@ -132,7 +132,7 @@ export default function() {
         typeof x === "function" ? -x.apply(this, arguments) : -x,
         typeof y === "function" ? -y.apply(this, arguments) : -y
       ), e, translateExtent);
-    }, p);
+    }, p, event);
   };
 
   function scale(transform, k) {
@@ -149,14 +149,14 @@ export default function() {
     return [(+extent[0][0] + +extent[1][0]) / 2, (+extent[0][1] + +extent[1][1]) / 2];
   }
 
-  function schedule(transition, transform, point) {
+  function schedule(transition, transform, point, event) {
     transition
-        .on("start.zoom", function() { gesture(this, arguments).start(); })
-        .on("interrupt.zoom end.zoom", function() { gesture(this, arguments).end(); })
+        .on("start.zoom", function() { gesture(this, [event, ...arguments]).start(); })
+        .on("interrupt.zoom end.zoom", function() { gesture(this, [event, ...arguments]).end(); })
         .tween("zoom", function() {
           var that = this,
               args = arguments,
-              g = gesture(that, args),
+              g = gesture(that, [event, ...args]),
               e = extent.apply(that, args),
               p = point == null ? centroid(e) : typeof point === "function" ? point.apply(that, args) : point,
               w = Math.max(e[1][0] - e[0][0], e[1][1] - e[0][1]),
@@ -179,7 +179,7 @@ export default function() {
     this.that = that;
     this.args = args;
     this.active = 0;
-    this.extent = extent.apply(that, args);
+    this.extent = extent.apply(that, [...args].slice(1, args.length));
     this.taps = 0;
   }
 
@@ -299,11 +299,11 @@ export default function() {
         p0 = pointer(event),
         p1 = t0.invert(p0),
         k1 = t0.k * (event.shiftKey ? 0.5 : 2),
-        t1 = constrain(translate(scale(t0, k1), p0, p1), extent.apply(this, arguments), translateExtent);
+        t1 = constrain(translate(scale(t0, k1), p0, p1), extent.apply(this, [...arguments].slice(1, arguments.length)), translateExtent);
 
     noevent(event);
-    if (duration > 0) select(this).transition().duration(duration).call(schedule, t1, p0);
-    else select(this).call(zoom.transform, t1);
+    if (duration > 0) select(this).transition().duration(duration).call(schedule, t1, p0, event);
+    else select(this).call(zoom.transform, t1, p0, event);
   }
 
   function touchstarted(event) {