Add WheelHandler

It can be used to change any qreal property of its target Item in
response to wheel rotation, or it can be used in other ways that involve
bindings but without a target item.

[ChangeLog][QtQuick][Event Handlers] Added WheelHandler, which handles
mouse wheel rotation by modifying arbitrary Item properties.

Fixes: QTBUG-68119
Change-Id: I247e2325ee993cc1b91a47fbd6c4ba0ffde7ad49
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

2 files changed, 87 insertions, 42 deletions

diff --git a/tests/manual/pointer/content/FakeFlickable.qml b/tests/manual/pointer/content/FakeFlickable.qml
index ffb5c4e914..636399ba2c 100644
--- a/tests/manual/pointer/content/FakeFlickable.qml
+++ b/tests/manual/pointer/content/FakeFlickable.qml
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the manual tests of the Qt Toolkit.
@@ -26,10 +26,12 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
+import QtQuick 2.14
+import Qt.labs.animation 1.0
 
 Item {
     id: root
+    objectName: "viewport"
     default property alias data: __contentItem.data
     property alias velocity: anim.velocity
     property alias contentX: __contentItem.x // sign is reversed compared to Flickable.contentX
@@ -45,52 +47,81 @@ Item {
         width: childrenRect.width
         height: childrenRect.height
 
-        property real xlimit: root.width - __contentItem.width
-        property real ylimit: root.height - __contentItem.height
+        BoundaryRule on x {
+            id: xbr
+            minimum: root.width - __contentItem.width
+            maximum: 0
+            minimumOvershoot: 100
+            maximumOvershoot: 100
+            overshootFilter: BoundaryRule.Peak
+        }
 
-        function returnToBounds() {
-            if (x > 0) {
-                returnXAnim.to = 0
-                returnXAnim.start()
-            } else if (x < xlimit) {
-                returnXAnim.to = xlimit
-                returnXAnim.start()
-            }
-            if (y > 0) {
-                returnYAnim.to = 0
-                returnYAnim.start()
-            } else if (y < ylimit) {
-                returnYAnim.to = ylimit
-                returnYAnim.start()
-            }
+        BoundaryRule on y {
+            id: ybr
+            minimum: root.height - __contentItem.height
+            maximum: 0
+            minimumOvershoot: 100
+            maximumOvershoot: 100
+            overshootFilter: BoundaryRule.Peak
         }
 
         DragHandler {
             id: dragHandler
-            onActiveChanged: if (!active) anim.restart(centroid.velocity)
+            onActiveChanged:
+                if (active) {
+                    anim.stop()
+                    root.flickStarted()
+                } else {
+                    var vel = centroid.velocity
+                    if (xbr.returnToBounds())
+                        vel.x = 0
+                    if (ybr.returnToBounds())
+                        vel.y = 0
+                    if (vel.x !== 0 || vel.y !== 0)
+                        anim.restart(vel)
+                    else
+                        root.flickEnded()
+                }
+        }
+        WheelHandler {
+            rotationScale: 15
+            property: "x"
+            orientation: Qt.Horizontal
+            acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad
+            onActiveChanged:
+                // emitting signals in both instances is redundant but hard to avoid
+                // when the touchpad is flicking along both axes
+                if (active) {
+                    anim.stop()
+                    root.flickStarted()
+                } else {
+                    xbr.returnToBounds()
+                    root.flickEnded()
+                }
+        }
+        WheelHandler {
+            rotationScale: 15
+            property: "y"
+            orientation: Qt.Vertical
+            acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad
+            onActiveChanged:
+                if (active) {
+                    anim.stop()
+                    root.flickStarted()
+                } else {
+                    ybr.returnToBounds()
+                    root.flickEnded()
+                }
         }
         MomentumAnimation {
             id: anim
             target: __contentItem
             onStarted: root.flickStarted()
             onStopped: {
-                __contentItem.returnToBounds()
+                xbr.returnToBounds()
+                ybr.returnToBounds()
                 root.flickEnded()
             }
         }
-        NumberAnimation {
-            id: returnXAnim
-            target: __contentItem
-            property: "x"
-            duration: 200
-            easing.type: Easing.OutQuad
-        }
-        NumberAnimation {
-            id: returnYAnim
-            target: __contentItem
-            property: "y"
-            duration: 200
-            easing.type: Easing.OutQuad
-        }
     }
 }
diff --git a/tests/manual/pointer/content/Slider.qml b/tests/manual/pointer/content/Slider.qml
index e3e02b0a2f..beb84b176b 100644
--- a/tests/manual/pointer/content/Slider.qml
+++ b/tests/manual/pointer/content/Slider.qml
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2017 The Qt Company Ltd.
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the manual tests of the Qt Toolkit.
@@ -26,7 +26,8 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
+import QtQuick 2.14
+import Qt.labs.animation 1.0
 
 Item {
     id: root
@@ -42,8 +43,16 @@ Item {
         objectName: label.text + " DragHandler"
         target: knob
         xAxis.enabled: false
-        yAxis.minimum: slot.y
-        yAxis.maximum: slot.height + slot.y - knob.height
+    }
+
+    WheelHandler {
+        id: wheelHandler
+        objectName: label.text + " WheelHandler"
+        acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad
+        invertible: false   // Don't let the system "natural scrolling" setting affect this
+        rotationScale: -0.5 // But make it go consistently in the same direction as the fingers or wheel, a bit slow
+        target: knob
+        property: "y"
     }
 
     Rectangle {
@@ -82,10 +91,10 @@ Item {
         height: root.width / 2
         width: implicitWidth / implicitHeight * height
         property bool programmatic: false
-        property real multiplier: root.maximumValue / (dragHandler.yAxis.maximum - dragHandler.yAxis.minimum)
-        onYChanged: if (!programmatic) root.value = root.maximumValue - (knob.y - dragHandler.yAxis.minimum) * multiplier
+        property real multiplier: root.maximumValue / (ybr.maximum - ybr.minimum)
+        onYChanged: if (!programmatic) root.value = root.maximumValue - (knob.y - ybr.minimum) * multiplier
         transformOrigin: Item.Center
-        function setValue(value) { knob.y = dragHandler.yAxis.maximum - value / knob.multiplier }
+        function setValue(value) { knob.y = ybr.maximum - value / knob.multiplier }
         TapHandler {
             id: tap
             objectName: label.text + " TapHandler"
@@ -95,6 +104,11 @@ Item {
                 root.tapped
             }
         }
+        BoundaryRule on y {
+            id: ybr
+            minimum: slot.y
+            maximum: slot.height + slot.y - knob.height
+        }
     }
 
     Text {