Document TapHandler.tapped and [single|double]Tapped eventPoint argument

Amends b8fd580cb3453b3850c36765c4b2537538d2f4f8 to add documentation.
The eventPoint is important to get ephemeral state from the pointing
device: which button was released (thus triggering the tap), which
device it was, and where the release occurred.  Users may expect to use
the point property, but QQuickHandlerPoint::reset(QQuickEventPoint *)
resets every property of the point at the same time, so the architecture
currently does not allow for mixed state, i.e. having correct button
state but still holding leftover position information.  It may be
surprising for users, but the changes to the point property are an
atomic transaction that occurs before the signal.

Task-number: QTBUG-61749
Task-number: QTBUG-64847
Change-Id: I33e0e232084beba8e10d8b02fa3bf85f36293358
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

2 files changed, 85 insertions, 6 deletions

diff --git a/src/quick/doc/snippets/pointerHandlers/tapHandlerOnTapped.qml b/src/quick/doc/snippets/pointerHandlers/tapHandlerOnTapped.qml
new file mode 100644
index 0000000000..f556c238da
--- /dev/null
+++ b/src/quick/doc/snippets/pointerHandlers/tapHandlerOnTapped.qml
@@ -0,0 +1,64 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
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+** accordance with the commercial license agreement provided with the
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+** and conditions see https://www.qt.io/terms-conditions. For further
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+**
+** 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
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+**     notice, this list of conditions and the following disclaimer in
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+**   * 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.
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+**
+** 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
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+** 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,
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+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick 2.12
+
+Rectangle {
+    width: 100
+    height: 100
+
+    TapHandler {
+        acceptedButtons: Qt.LeftButton | Qt.RightButton
+        onTapped: console.log("tapped", eventPoint.event.device.name,
+                              "button", eventPoint.event.button,
+                              "@", eventPoint.scenePosition)
+    }
+}
+//![0]
diff --git a/src/quick/handlers/qquicktaphandler.cpp b/src/quick/handlers/qquicktaphandler.cpp
index 41ac294df3..73c559c998 100644
--- a/src/quick/handlers/qquicktaphandler.cpp
+++ b/src/quick/handlers/qquicktaphandler.cpp
@@ -380,35 +380,50 @@ void QQuickTapHandler::updateTimeHeld()
 */
 
 /*!
-    \qmlsignal QtQuick::TapHandler::tapped
+    \qmlsignal QtQuick::TapHandler::tapped(EventPoint eventPoint)
 
     This signal is emitted each time the \c parent Item is tapped.
 
     That is, if you press and release a touchpoint or button within a time
     period less than \l longPressThreshold, while any movement does not exceed
     the drag threshold, then the \c tapped signal will be emitted at the time
-    of release.
+    of release.  The \c eventPoint signal parameter contains information
+    from the release event about the point that was tapped:
+
+    \snippet pointerHandlers/tapHandlerOnTapped.qml 0
+
+    \note At the time this signal is emitted, \l point has been reset
+    (all coordinates are \c 0).
 */
 
 /*!
-    \qmlsignal QtQuick::TapHandler::singleTapped
+    \qmlsignal QtQuick::TapHandler::singleTapped(EventPoint eventPoint)
     \since 5.11
 
     This signal is emitted when the \c parent Item is tapped once.
     After an amount of time greater than QStyleHints::mouseDoubleClickInterval,
     it can be tapped again; but if the time until the next tap is less,
-    \l tapCount will increase.
+    \l tapCount will increase. The \c eventPoint signal parameter contains
+    information from the release event about the point that was tapped.
+
+    \note At the time this signal is emitted, \l point has been reset
+    (all coordinates are \c 0).
 */
 
 /*!
-    \qmlsignal QtQuick::TapHandler::doubleTapped
+    \qmlsignal QtQuick::TapHandler::doubleTapped(EventPoint eventPoint)
     \since 5.11
 
     This signal is emitted when the \c parent Item is tapped twice within a
     short span of time (QStyleHints::mouseDoubleClickInterval) and distance
     (QPlatformTheme::MouseDoubleClickDistance or
     QPlatformTheme::TouchDoubleTapDistance). This signal always occurs after
-    \l singleTapped, \l tapped, and \l tapCountChanged.
+    \l singleTapped, \l tapped, and \l tapCountChanged. The \c eventPoint
+    signal parameter contains information from the release event about the
+    point that was tapped.
+
+    \note At the time this signal is emitted, \l point has been reset
+    (all coordinates are \c 0).
 */
 
 /*!