1// Copyright (C) 2017 The Qt Company Ltd.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3
4#include "qquickpointhandler_p.h"
5#include <private/qquickwindow_p.h>
6#include <QDebug>
7
8QT_BEGIN_NAMESPACE
9
10/*!
11 \qmltype PointHandler
12 \instantiates QQuickPointHandler
13 \inherits SinglePointHandler
14 \inqmlmodule QtQuick
15 \ingroup qtquick-input-handlers
16 \brief Handler for reacting to a single touchpoint.
17
18 PointHandler can be used to show feedback about a touchpoint or the mouse
19 position, or to otherwise react to pointer events.
20
21 When a press event occurs, each instance of PointHandler chooses a
22 single point which is not yet "taken" at that moment: if the press
23 occurs within the bounds of the \l {PointerHandler::parent}, and
24 no sibling PointHandler within the same \l {PointerHandler::parent}
25 has yet acquired a passive grab on that point, and if the other
26 constraints such as \l {PointerDeviceHandler::acceptedButtons}{acceptedButtons}, \l {PointerDeviceHandler::acceptedDevices}{acceptedDevices} etc.
27 are satisfied, it's
28 eligible, and the PointHandler then acquires a passive grab. In
29 this way, the \l {PointerHandler::parent} acts like an exclusive
30 group: there can be multiple instances of PointHandler, and the
31 set of pressed touchpoints will be distributed among them. Each
32 PointHandler which has chosen a point to track has its \l active
33 property \c true. It then continues to track its chosen point
34 until release: the properties of the \l point will be kept
35 up-to-date. Any Item can bind to these properties, and thereby
36 follow the point's movements.
37
38 By being only a passive grabber, it has the ability to keep independent
39 oversight of all movements. The passive grab cannot be stolen or overridden
40 even when other gestures are detected and exclusive grabs occur.
41
42 If your goal is orthogonal surveillance of eventpoints, an older
43 alternative was QObject::installEventFilter(), but that has never been a
44 built-in QtQuick feature: it requires some C++ code, such as a QQuickItem
45 subclass. PointHandler is more efficient than that, because only pointer
46 events will be delivered to it, during the course of normal event delivery
47 in QQuickWindow; whereas an event filter needs to filter all QEvents of all
48 types, and thus sets itself up as a potential event delivery bottleneck.
49
50 One possible use case is to add this handler to a transparent Item which is
51 on top of the rest of the scene (by having a high \l{Item::z} {z} value),
52 so that when a point is freshly pressed, it will be delivered to that Item
53 and its handlers first, providing the opportunity to take the passive grab
54 as early as possible. Such an item (like a pane of glass over the whole UI)
55 can be a convenient parent for other Items which visualize the kind of reactive
56 feedback which must always be on top; and likewise it can be the parent for
57 popups, popovers, dialogs and so on. If it will be used in that way, it can
58 be helpful for your main.cpp to use QQmlContext::setContextProperty() to
59 make the "glass pane" accessible by ID to the entire UI, so that other
60 Items and PointHandlers can be reparented to it.
61
62 \snippet pointerHandlers/pointHandler.qml 0
63
64 Like all input handlers, a PointHandler has a \l target property, which
65 may be used as a convenient place to put a point-tracking Item; but
66 PointHandler will not automatically manipulate the \c target item in any way.
67 You need to use bindings to make it react to the \l point.
68
69 \note On macOS, PointHandler does not react to multiple fingers on the
70 trackpad by default, although it does react to a pressed point (mouse position).
71 That is because macOS can provide either native gesture recognition, or raw
72 touchpoints, but not both. We prefer to use the native gesture event in
73 PinchHandler, so we do not want to disable it by enabling touch. However
74 MultiPointTouchArea does enable touch, thus disabling native gesture
75 recognition within the entire window; so it's an alternative if you only
76 want to react to all the touchpoints but do not require the smooth
77 native-gesture experience.
78
79 \sa MultiPointTouchArea, HoverHandler, {Qt Quick Examples - Pointer Handlers}
80*/
81
82QQuickPointHandler::QQuickPointHandler(QQuickItem *parent)
83 : QQuickSinglePointHandler(parent)
84{
85 setIgnoreAdditionalPoints();
86}
87
88bool QQuickPointHandler::wantsEventPoint(const QPointerEvent *event, const QEventPoint &point)
89{
90 // On press, we want it unless a sibling of the same type also does.
91 if (point.state() == QEventPoint::Pressed && QQuickSinglePointHandler::wantsEventPoint(event, point)) {
92 for (const QObject *grabber : event->passiveGrabbers(point)) {
93 if (grabber && grabber->parent() == parent() &&
94 grabber->metaObject()->className() == metaObject()->className())
95 return false;
96 }
97 return true;
98 }
99 // If we've already been interested in a point, stay interested, even if it has strayed outside bounds.
100 return (point.state() != QEventPoint::Pressed &&
101 QQuickSinglePointHandler::point().id() == point.id());
102}
103
104void QQuickPointHandler::handleEventPoint(QPointerEvent *event, QEventPoint &point)
105{
106 switch (point.state()) {
107 case QEventPoint::Pressed:
108 if (QQuickDeliveryAgentPrivate::isTouchEvent(ev: event) ||
109 (static_cast<const QSinglePointEvent *>(event)->buttons() & acceptedButtons()) != Qt::NoButton) {
110 setPassiveGrab(event, point);
111 setActive(true);
112 }
113 break;
114 case QEventPoint::Released:
115 if (QQuickDeliveryAgentPrivate::isTouchEvent(ev: event) ||
116 (static_cast<const QSinglePointEvent *>(event)->buttons() & acceptedButtons()) == Qt::NoButton)
117 setActive(false);
118 break;
119 default:
120 break;
121 }
122 point.setAccepted(false); // Just lurking... don't interfere with propagation
123 emit translationChanged();
124 QQuickSinglePointHandler::handleEventPoint(event, point);
125}
126
127QVector2D QQuickPointHandler::translation() const
128{
129 return QVector2D(point().position() - point().pressPosition());
130}
131
132/*!
133 \qmlproperty flags PointHandler::acceptedButtons
134
135 The mouse buttons that can activate this PointHandler.
136
137 By default, this property is set to \l {QtQuick::MouseEvent::button} {Qt.LeftButton}.
138 It can be set to an OR combination of mouse buttons, and will ignore events
139 in which other buttons are pressed or held.
140
141 \snippet pointerHandlers/pointHandlerAcceptedButtons.qml 0
142
143 \note On a touchscreen, there are no buttons, so this property does not
144 prevent PointHandler from reacting to touchpoints.
145*/
146
147/*!
148 \qmlproperty flags PointHandler::acceptedDevices
149
150 The types of pointing devices that can activate this PointHandler.
151
152 By default, this property is set to
153 \l{QInputDevice::DeviceType}{PointerDevice.AllDevices}.
154 If you set it to an OR combination of device types, it will ignore events
155 from non-matching \l {PointerDevice}{devices}:
156
157 \snippet pointerHandlers/pointHandler.qml 1
158*/
159
160/*!
161 \qmlproperty flags PointHandler::acceptedPointerTypes
162
163 The types of pointing instruments (finger, stylus, eraser, etc.)
164 that can activate this PointHandler.
165
166 By default, this property is set to
167 \l {QPointingDevice::PointerType} {PointerDevice.AllPointerTypes}.
168 If you set it to an OR combination of device types, it will ignore events
169 from non-matching \l {PointerDevice}{devices}:
170
171 \snippet pointerHandlers/pointHandlerCanvasDrawing.qml 0
172
173 The \l {Qt Quick Examples - Pointer Handlers} includes a more complex example for
174 drawing on a Canvas with a graphics tablet.
175*/
176
177/*!
178 \qmlproperty flags PointHandler::acceptedModifiers
179
180 If this property is set, PointHandler requires the given keyboard modifiers
181 to be pressed in order to react to \l {PointerEvent}{PointerEvents}, and
182 otherwise ignores them.
183
184 If this property is set to \c Qt.KeyboardModifierMask (the default value),
185 then PointHandler ignores the modifier keys.
186
187 For example, an \l [QML] Item could have two handlers, one of which is
188 enabled only if the required keyboard modifier is pressed:
189
190 \snippet pointerHandlers/pointHandlerAcceptedModifiers.qml 0
191
192 If you set \c acceptedModifiers to an OR combination of modifier keys,
193 it means \e all of those modifiers must be pressed to activate the handler.
194
195 The available modifiers are as follows:
196
197 \value NoModifier No modifier key is allowed.
198 \value ShiftModifier A Shift key on the keyboard must be pressed.
199 \value ControlModifier A Ctrl key on the keyboard must be pressed.
200 \value AltModifier An Alt key on the keyboard must be pressed.
201 \value MetaModifier A Meta key on the keyboard must be pressed.
202 \value KeypadModifier A keypad button must be pressed.
203 \value GroupSwitchModifier X11 only (unless activated on Windows by a command line argument).
204 A Mode_switch key on the keyboard must be pressed.
205 \value KeyboardModifierMask The handler does not care which modifiers are pressed.
206
207 \sa Qt::KeyboardModifier
208*/
209
210/*!
211 \readonly
212 \qmlproperty bool PointHandler::active
213
214 This holds \c true whenever the constraints are satisfied and this
215 PointHandler is reacting. This means that it is keeping its properties
216 up-to-date according to the movements of the \l {eventPoint}{eventPoints}
217 that satisfy the constraints.
218*/
219
220/*!
221 \internal
222 \qmlproperty flags PointHandler::dragThreshold
223
224 This property is not used in PointHandler.
225*/
226
227/*!
228 \qmlproperty real PointHandler::margin
229
230 The margin beyond the bounds of the \l {PointerHandler::parent}{parent}
231 item within which an \l eventPoint can activate this handler.
232
233 The default value is \c 0.
234
235 \snippet pointerHandlers/pointHandlerMargin.qml 0
236*/
237
238/*!
239 \qmlproperty real PointHandler::target
240
241 A property that can conveniently hold an Item to be manipulated or to show
242 feedback. Unlike other \l {Qt Quick Input Handlers}{Pointer Handlers},
243 PointHandler does not do anything with the \c target on its own: you
244 usually need to create reactive bindings to properties such as
245 \l SinglePointHandler::point and \l PointHandler::active. If you declare
246 an Item instance here, you need to explicitly set its \l {Item::}{parent},
247 because PointHandler is not an Item.
248
249 By default, it is the same as the \l {PointerHandler::}{parent}, the Item
250 within which the handler is declared.
251*/
252
253QT_END_NAMESPACE
254
255#include "moc_qquickpointhandler_p.cpp"
256

source code of qtdeclarative/src/quick/handlers/qquickpointhandler.cpp