Allow very small twodrag and pinch gestures

Before this commit, we strictly required the user to make a ~50 pixel
move in order to get these two gestures. We can get a more precise
experience if we allow very small gestures as well. This can be achieved
by making better use of our "_twoTouchTimeout".

Our two touch timeout handling was written to handle this well anyway.
We can distinguish between drag and pinch using the angle.

core/input/gesturehandler.js

@@ -186,14 +186,14 @@ export default class GestureHandler {
         }
 
         if (!this._hasDetectedGesture()) {
-            // Ignore moves smaller than the minimum threshold
-            if (Math.hypot(deltaX, deltaY) < GH_MOVE_THRESHOLD) {
-                return;
-            }
 
-            // Can't be a tap or long press as we've seen movement
-            this._state &= ~(GH_ONETAP | GH_TWOTAP | GH_THREETAP | GH_LONGPRESS);
-            this._stopLongpressTimeout();
+            let deltaMove = Math.hypot(deltaX, deltaY);
+
+            // Can't be a tap or long press if we've seen movement
+            if (deltaMove >= GH_MOVE_THRESHOLD) {
+                this._state &= ~(GH_ONETAP | GH_TWOTAP | GH_THREETAP | GH_LONGPRESS);
+                this._stopLongpressTimeout();
+            }
 
             if (this._tracked.length !== 1) {
                 this._state &= ~(GH_DRAG);
@@ -213,10 +213,10 @@ export default class GestureHandler {
                 let prevDeltaMove = Math.hypot(prevTouch.firstX - prevTouch.lastX,
                                                prevTouch.firstY - prevTouch.lastY);
 
-                // We know that the current touch moved far enough,
-                // but unless both touches moved further than their
-                // threshold we don't want to disqualify any gestures
-                if (prevDeltaMove > GH_MOVE_THRESHOLD) {
+                // Unless both touches moved further than their threshold we
+                // don't want to disqualify any gestures right now
+                if (deltaMove > GH_MOVE_THRESHOLD &&
+                    prevDeltaMove > GH_MOVE_THRESHOLD) {
 
                     // The angle difference between the direction of the touch points
                     let deltaAngle = Math.abs(touch.angle - prevTouch.angle);
@@ -234,7 +234,8 @@ export default class GestureHandler {
                     }
                 } else if (!this._isTwoTouchTimeoutRunning()) {
                     // We can't determine the gesture right now, let's
-                    // wait and see if more events are on their way
+                    // wait and see if more events are on their way.
+                    // If not, we'll have to decide which gesture it is.
                     this._startTwoTouchTimeout();
                 }
             }

tests/test.gesturehandler.js

@@ -580,7 +580,7 @@ describe('Gesture handler', function () {
             touchStart(1, 50.0, 40.0);
             touchStart(2, 60.0, 40.0);
             touchMove(1, 80.0, 40.0);
-            touchMove(2, 110.0, 40.0);
+            touchMove(2, 90.0, 40.0);
 
             expect(gestures).to.not.have.been.called;
 
@@ -601,15 +601,15 @@ describe('Gesture handler', function () {
                               detail: { type: 'twodrag',
                                         clientX: 55.0,
                                         clientY: 40.0,
-                                        magnitudeX: 40.0,
+                                        magnitudeX: 30.0,
                                         magnitudeY: 0.0 } }));
         });
 
         it('should handle slow vertical two finger drag', function () {
             touchStart(1, 40.0, 40.0);
             touchStart(2, 40.0, 60.0);
             touchMove(2, 40.0, 80.0);
-            touchMove(1, 40.0, 100.0);
+            touchMove(1, 40.0, 80.0);
 
             expect(gestures).to.not.have.been.called;
 
@@ -631,14 +631,14 @@ describe('Gesture handler', function () {
                                         clientX: 40.0,
                                         clientY: 50.0,
                                         magnitudeX: 0.0,
-                                        magnitudeY: 40.0 } }));
+                                        magnitudeY: 30.0 } }));
         });
 
         it('should handle slow diagonal two finger drag', function () {
             touchStart(1, 50.0, 40.0);
             touchStart(2, 40.0, 60.0);
             touchMove(1, 70.0, 60.0);
-            touchMove(2, 90.0, 110.0);
+            touchMove(2, 60.0, 80.0);
 
             expect(gestures).to.not.have.been.called;
 
@@ -659,8 +659,8 @@ describe('Gesture handler', function () {
                               detail: { type: 'twodrag',
                                         clientX: 45.0,
                                         clientY: 50.0,
-                                        magnitudeX: 35.0,
-                                        magnitudeY: 35.0 } }));
+                                        magnitudeX: 20.0,
+                                        magnitudeY: 20.0 } }));
         });
 
         it('should ignore too slow two finger drag', function () {
@@ -783,7 +783,7 @@ describe('Gesture handler', function () {
         it('should handle pinching inwards slowly', function () {
             touchStart(1, 0.0, 0.0);
             touchStart(2, 130.0, 130.0);
-            touchMove(1, 50.0, 40.0);
+            touchMove(1, 30.0, 20.0);
             touchMove(2, 100.0, 130.0);
 
             expect(gestures).to.not.have.been.called;
@@ -805,14 +805,14 @@ describe('Gesture handler', function () {
                               detail: { type: 'pinch',
                                         clientX: 65.0,
                                         clientY: 65.0,
-                                        magnitudeX: 50.0,
-                                        magnitudeY: 90.0 } }));
+                                        magnitudeX: 70.0,
+                                        magnitudeY: 110.0 } }));
         });
 
         it('should handle pinching outwards slowly', function () {
             touchStart(1, 100.0, 130.0);
             touchStart(2, 110.0, 130.0);
-            touchMove(2, 200.0, 130.0);
+            touchMove(2, 130.0, 130.0);
 
             expect(gestures).to.not.have.been.called;
 
@@ -833,7 +833,7 @@ describe('Gesture handler', function () {
                               detail: { type: 'pinch',
                                         clientX: 105.0,
                                         clientY: 130.0,
-                                        magnitudeX: 100.0,
+                                        magnitudeX: 30.0,
                                         magnitudeY: 0.0 } }));
         });