doc: Add snippets and animations illustrating TapHandler.GesturePolicy

People are constantly confused by GesturePolicy and its default value,
so we really need a "glanceable" reference in the docs to show the
differences between use cases.

Also clarify the pitfalls with the default DragThreshold value.

We switch from the \value tag to a 2-column \table because the \image
would otherwise break the table, and also because it saves space and
acts as a meaningful reminder to have the animation right under the
enum value that is being documented.

Task-number: QTBUG-70397
Task-number: QTBUG-73262
Task-number: QTBUG-100534
Task-number: QTBUG-107239
Task-number: QTBUG-111310
Change-Id: I1ff45f58a8a8edf55f4a8696d881aa9e0bedcfe3
Reviewed-by: Oliver Eftevaag <oliver.eftevaag@qt.io>
(cherry picked from commit a6e196ce9cd327df53ef9b9db3020f7775ee1754)
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

8 files changed, 365 insertions, 29 deletions

diff --git a/src/quick/doc/images/pointerHandlers/tapHandlerButtonReleaseWithinBounds.webp b/src/quick/doc/images/pointerHandlers/tapHandlerButtonReleaseWithinBounds.webp
new file mode 100644
index 0000000000..3edab7d7a1
--- /dev/null
+++ b/src/quick/doc/images/pointerHandlers/tapHandlerButtonReleaseWithinBounds.webp
diff --git a/src/quick/doc/images/pointerHandlers/tapHandlerButtonWithinBounds.webp b/src/quick/doc/images/pointerHandlers/tapHandlerButtonWithinBounds.webp
new file mode 100644
index 0000000000..05cb2f2276
--- /dev/null
+++ b/src/quick/doc/images/pointerHandlers/tapHandlerButtonWithinBounds.webp
diff --git a/src/quick/doc/images/pointerHandlers/tapHandlerOverlappingButtons.webp b/src/quick/doc/images/pointerHandlers/tapHandlerOverlappingButtons.webp
new file mode 100644
index 0000000000..0455097159
--- /dev/null
+++ b/src/quick/doc/images/pointerHandlers/tapHandlerOverlappingButtons.webp
diff --git a/src/quick/doc/snippets/pointerHandlers/tapHandlerButtonReleaseWithinBounds.qml b/src/quick/doc/snippets/pointerHandlers/tapHandlerButtonReleaseWithinBounds.qml
new file mode 100644
index 0000000000..a6b1673d4c
--- /dev/null
+++ b/src/quick/doc/snippets/pointerHandlers/tapHandlerButtonReleaseWithinBounds.qml
@@ -0,0 +1,98 @@
+/****************************************************************************
+**
+** Copyright (C) 2023 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick
+
+Item {
+    width: 120; height: 80
+
+    component Button : Rectangle {
+        id: button
+        signal clicked
+        property alias text: buttonLabel.text
+
+        width: 80
+        height: 40
+        radius: 3
+        property color dark: Qt.darker(palette.button, 1.3)
+        gradient: Gradient {
+            GradientStop { position: 0.0; color: tapHandler.pressed ? dark : palette.button }
+            GradientStop { position: 1.0; color: dark }
+        }
+
+        SequentialAnimation on border.width {
+            id: tapFlash
+            running: false
+            loops: 3
+            PropertyAction { value: 2 }
+            PauseAnimation { duration: 100 }
+            PropertyAction { value: 0 }
+            PauseAnimation { duration: 100 }
+        }
+
+        //![1]
+        TapHandler {
+            id: tapHandler
+            gesturePolicy: TapHandler.ReleaseWithinBounds
+            onTapped: tapFlash.start()
+        }
+        //![1]
+
+        Text {
+            id: buttonLabel
+            text: "Click Me"
+            color: palette.buttonText
+            anchors.centerIn: parent
+        }
+    }
+
+    Button { x: 10; y: 10 }
+}
+//![0]
diff --git a/src/quick/doc/snippets/pointerHandlers/tapHandlerButtonWithinBounds.qml b/src/quick/doc/snippets/pointerHandlers/tapHandlerButtonWithinBounds.qml
new file mode 100644
index 0000000000..f2e968599c
--- /dev/null
+++ b/src/quick/doc/snippets/pointerHandlers/tapHandlerButtonWithinBounds.qml
@@ -0,0 +1,98 @@
+/****************************************************************************
+**
+** Copyright (C) 2023 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick
+
+Item {
+    width: 120; height: 80
+
+    component Button : Rectangle {
+        id: button
+        signal clicked
+        property alias text: buttonLabel.text
+
+        width: 80
+        height: 40
+        radius: 3
+        property color dark: Qt.darker(palette.button, 1.3)
+        gradient: Gradient {
+            GradientStop { position: 0.0; color: tapHandler.pressed ? dark : palette.button }
+            GradientStop { position: 1.0; color: dark }
+        }
+
+        SequentialAnimation on border.width {
+            id: tapFlash
+            running: false
+            loops: 3
+            PropertyAction { value: 2 }
+            PauseAnimation { duration: 100 }
+            PropertyAction { value: 0 }
+            PauseAnimation { duration: 100 }
+        }
+
+        //![1]
+        TapHandler {
+            id: tapHandler
+            gesturePolicy: TapHandler.WithinBounds
+            onTapped: tapFlash.start()
+        }
+        //![1]
+
+        Text {
+            id: buttonLabel
+            text: "Click Me"
+            color: palette.buttonText
+            anchors.centerIn: parent
+        }
+    }
+
+    Button { x: 10; y: 10 }
+}
+//![0]
diff --git a/src/quick/doc/snippets/pointerHandlers/tapHandlerOverlappingButtons.qml b/src/quick/doc/snippets/pointerHandlers/tapHandlerOverlappingButtons.qml
new file mode 100644
index 0000000000..993330a5ec
--- /dev/null
+++ b/src/quick/doc/snippets/pointerHandlers/tapHandlerOverlappingButtons.qml
@@ -0,0 +1,98 @@
+/****************************************************************************
+**
+** Copyright (C) 2023 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick
+
+Item {
+    width: 120; height: 80
+
+    component Button : Rectangle {
+        signal clicked
+        property alias text: buttonLabel.text
+
+        width: 80
+        height: 40
+        radius: 3
+        property color dark: Qt.darker(palette.button, 1.3)
+        gradient: Gradient {
+            GradientStop { position: 0.0; color: tapHandler.pressed ? dark : palette.button }
+            GradientStop { position: 1.0; color: dark }
+        }
+
+        SequentialAnimation on border.width {
+            id: tapFlash
+            running: false
+            loops: 3
+            PropertyAction { value: 2 }
+            PauseAnimation { duration: 100 }
+            PropertyAction { value: 0 }
+            PauseAnimation { duration: 100 }
+        }
+
+        //![1]
+        TapHandler {
+            id: tapHandler
+            gesturePolicy: TapHandler.DragThreshold // the default
+            onTapped: tapFlash.start()
+        }
+        //![1]
+
+        Text {
+            id: buttonLabel
+            text: "Click Me"
+            color: palette.buttonText
+            anchors.centerIn: parent
+        }
+    }
+
+    Button { x: 10; y: 10 }
+    Button { x: 30; y: 30 }
+}
+//![0]
diff --git a/src/quick/doc/src/concepts/inputhandlers/qtquickhandlers-index.qdoc b/src/quick/doc/src/concepts/inputhandlers/qtquickhandlers-index.qdoc
index bf889a9066..cca6b27ecf 100644
--- a/src/quick/doc/src/concepts/inputhandlers/qtquickhandlers-index.qdoc
+++ b/src/quick/doc/src/concepts/inputhandlers/qtquickhandlers-index.qdoc
@@ -94,7 +94,8 @@
     PointHandler) can work only with passive grabs; others require exclusive
     grabs; and others can "lurk" with passive grabs until they detect that a
     gesture is being performed, and then make the transition from passive to
-    exclusive grab.
+    exclusive grab. TapHandler's grabbing behavior is
+    \l {TapHandler::gesturePolicy}{configurable}.
 
     When a grab transition is requested, \l PointerHandler::grabPermissions,
     \l QQuickItem::keepMouseGrab() and \l QQuickItem::keepTouchGrab() control
diff --git a/src/quick/handlers/qquicktaphandler.cpp b/src/quick/handlers/qquicktaphandler.cpp
index 38dd64f500..db124fb474 100644
--- a/src/quick/handlers/qquicktaphandler.cpp
+++ b/src/quick/handlers/qquicktaphandler.cpp
@@ -229,34 +229,75 @@ void QQuickTapHandler::timerEvent(QTimerEvent *event)
 
     The \c gesturePolicy also affects grab behavior as described below.
 
-    \value TapHandler.DragThreshold
-           (the default value) The event point must not move significantly.
-           If the mouse, finger or stylus moves past the system-wide drag
-           threshold (QStyleHints::startDragDistance), the tap gesture is
-           canceled, even if the button or finger is still pressed. This policy
-           can be useful whenever TapHandler needs to cooperate with other
-           input handlers (for example \l DragHandler) or event-handling Items
-           (for example QtQuick Controls), because in this case TapHandler
-           will not take the exclusive grab, but merely a
-           \l {QPointerEvent::addPassiveGrabber()}{passive grab}.
-
-    \value TapHandler.WithinBounds
-           If the event point leaves the bounds of the \c parent Item, the tap
-           gesture is canceled. The TapHandler will take the
-           \l {QPointerEvent::setExclusiveGrabber}{exclusive grab} on
-           press, but will release the grab as soon as the boundary constraint
-           is no longer satisfied.
-
-    \value TapHandler.ReleaseWithinBounds
-           At the time of release (the mouse button is released or the finger
-           is lifted), if the event point is outside the bounds of the
-           \c parent Item, a tap gesture is not recognized. This corresponds to
-           typical behavior for button widgets: you can cancel a click by
-           dragging outside the button, and you can also change your mind by
-           dragging back inside the button before release. Note that it's
-           necessary for TapHandler to take the
-           \l {QPointerEvent::setExclusiveGrabber}{exclusive grab} on press
-           and retain it until release in order to detect this gesture.
+    \table
+    \header
+        \li Constant
+        \li Description
+    \row
+        \li \c TapHandler.DragThreshold
+            \image pointerHandlers/tapHandlerOverlappingButtons.webp
+            Grab on press: \e passive
+        \li (the default value) The \l eventPoint must not move significantly.
+            If the mouse, finger or stylus moves past the system-wide drag
+            threshold (QStyleHints::startDragDistance), the tap gesture is
+            canceled, even if the device or finger is still pressed. This policy
+            can be useful whenever TapHandler needs to cooperate with other
+            input handlers (for example \l DragHandler) or event-handling Items
+            (for example \l {Qt Quick Controls}), because in this case TapHandler
+            will not take the exclusive grab, but merely a
+            \l {QPointerEvent::addPassiveGrabber()}{passive grab}.
+            That is, \c DragThreshold is especially useful to \e augment
+            existing behavior: it reacts to tap/click/long-press even when
+            another item or handler is already reacting, perhaps even in a
+            different layer of the UI. The following snippet shows one
+            TapHandler as used in one component; but if we stack up two
+            instances of the component, you will see the handlers in both of them
+            react simultaneously when a press occurs over both of them, because
+            the passive grab does not stop event propagation:
+            \quotefromfile pointerHandlers/tapHandlerOverlappingButtons.qml
+            \skipto Item
+            \printuntil component Button
+            \skipto TapHandler
+            \printuntil }
+            \skipuntil Text {
+            \skipuntil }
+            \printuntil Button
+            \printuntil Button
+            \printuntil }
+
+    \row
+        \li \c TapHandler.WithinBounds
+            \image pointerHandlers/tapHandlerButtonWithinBounds.webp
+            Grab on press: \e exclusive
+        \li If the \l eventPoint leaves the bounds of the \c parent Item, the tap
+            gesture is canceled. The TapHandler will take the
+            \l {QPointerEvent::setExclusiveGrabber}{exclusive grab} on
+            press, but will release the grab as soon as the boundary constraint
+            is no longer satisfied.
+            \snippet pointerHandlers/tapHandlerButtonWithinBounds.qml 1
+
+    \row
+        \li \c TapHandler.ReleaseWithinBounds
+            \image pointerHandlers/tapHandlerButtonReleaseWithinBounds.webp
+            Grab on press: \e exclusive
+        \li At the time of release (the mouse button is released or the finger
+            is lifted), if the \l eventPoint is outside the bounds of the
+            \c parent Item, a tap gesture is not recognized. This corresponds to
+            typical behavior for button widgets: you can cancel a click by
+            dragging outside the button, and you can also change your mind by
+            dragging back inside the button before release. Note that it's
+            necessary for TapHandler to take the
+            \l {QPointerEvent::setExclusiveGrabber}{exclusive grab} on press
+            and retain it until release in order to detect this gesture.
+            \snippet pointerHandlers/tapHandlerButtonReleaseWithinBounds.qml 1
+    \endtable
+
+    \note If you find that TapHandler is reacting in cases that conflict with
+    some other behavior, the first thing you should try is to think about which
+    \c gesturePolicy is appropriate. If you cannot fix it by changing \c gesturePolicy,
+    some cases are better served by adjusting \l {PointerHandler::}{grabPermissions},
+    either in this handler, or in another handler that should \e prevent TapHandler
+    from reacting.
 */
 void QQuickTapHandler::setGesturePolicy(QQuickTapHandler::GesturePolicy gesturePolicy)
 {