Introduce PinchHandler

Similar to PinchArea but with improvements:
- Allows rotating and scaling about an arbitrary point rather than the center
- It's possible to require more than 2 fingers.  E.g. maybe you use
  3 fingers to manage a window, 2 fingers to manipulate content inside.
  This could be achieved with two independent PinchHandlers.

Change-Id: Ifd40cfee115d7bc298378b26a58318bea40a8230
Reviewed-by: Jan Arve Sæther <jan-arve.saether@theqtcompany.com>

1 files changed, 201 insertions, 0 deletions

diff --git a/src/quick/handlers/qquickpinchhandler.cpp b/src/quick/handlers/qquickpinchhandler.cpp
new file mode 100644
index 0000000000..ddec7eee87
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+++ b/src/quick/handlers/qquickpinchhandler.cpp
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+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQuick module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qquickpinchhandler_p.h"
+#include <QtQuick/qquickwindow.h>
+#include <private/qsgadaptationlayer_p.h>
+#include <private/qquickitem_p.h>
+#include <private/qguiapplication_p.h>
+#include <private/qquickwindow_p.h>
+#include <QEvent>
+#include <QMouseEvent>
+#include <QDebug>
+#include <qpa/qplatformnativeinterface.h>
+
+QT_BEGIN_NAMESPACE
+
+Q_LOGGING_CATEGORY(lcPinchHandler, "qt.quick.handler.pinch")
+
+/*!
+    \qmltype PinchHandler
+    \instantiates QQuickPinchHandler
+    \inqmlmodule QtQuick
+    \ingroup qtquick-handlers
+    \brief Handler for pinch gestures
+
+    PinchHandler is a handler that is used to interactively rotate and zoom an Item.
+*/
+
+QQuickPinchHandler::QQuickPinchHandler(QObject *parent)
+    : QQuickMultiPointerHandler(parent, 2)
+    , m_startScale(1)
+    , m_startRotation(0)
+    , m_minimumScale(-qInf())
+    , m_maximumScale(qInf())
+    , m_minimumRotation(-qInf())
+    , m_maximumRotation(qInf())
+    , m_pinchOrigin(PinchCenter)
+{
+    connect(this, &QQuickPinchHandler::activeChanged, this, &QQuickPinchHandler::onActiveChanged);
+    connect(this, &QQuickPinchHandler::targetChanged, this, &QQuickPinchHandler::onTargetChanged);
+}
+
+QQuickPinchHandler::~QQuickPinchHandler()
+{
+}
+
+void QQuickPinchHandler::setMinimumScale(qreal minimumScale)
+{
+    if (m_minimumScale == minimumScale)
+        return;
+
+    m_minimumScale = minimumScale;
+    emit minimumScaleChanged();
+}
+
+void QQuickPinchHandler::setMaximumScale(qreal maximumScale)
+{
+    if (m_maximumScale == maximumScale)
+        return;
+
+    m_maximumScale = maximumScale;
+    emit maximumScaleChanged();
+}
+
+void QQuickPinchHandler::setMinimumRotation(qreal minimumRotation)
+{
+    if (m_minimumRotation == minimumRotation)
+        return;
+
+    m_minimumRotation = minimumRotation;
+    emit minimumRotationChanged();
+}
+
+void QQuickPinchHandler::setMaximumRotation(qreal maximumRotation)
+{
+    if (m_maximumRotation == maximumRotation)
+        return;
+
+    m_maximumRotation = maximumRotation;
+    emit maximumRotationChanged();
+}
+
+void QQuickPinchHandler::setPinchOrigin(QQuickPinchHandler::PinchOrigin pinchOrigin)
+{
+    if (m_pinchOrigin == pinchOrigin)
+        return;
+
+    m_pinchOrigin = pinchOrigin;
+    emit pinchOriginChanged();
+}
+
+/*!
+    \qmlproperty QQuickPinchHandler::minimumTouchPoints
+
+    The pinch begins when this number of fingers are pressed.
+    Until then, PinchHandler tracks the positions of any pressed fingers,
+    but if it's an insufficient number, it does not scale or rotate
+    its \l target, and the \l active property will remain false.
+*/
+
+/*!
+    \qmlproperty QQuickPinchHandler::active
+*/
+
+void QQuickPinchHandler::onActiveChanged()
+{
+    if (active()) {
+        m_startScale = m_scaleTransform.xScale(); // TODO incompatible with independent x/y scaling
+        m_startRotation = m_rotationTransform.angle();
+        qCInfo(lcPinchHandler) << "activated with starting scale" << m_startScale << "rotation" << m_startRotation;
+        grabPoints(m_currentPoints);
+    }
+}
+
+void QQuickPinchHandler::onTargetChanged()
+{
+    if (target()) {
+        // TODO if m_target was previously set differently,
+        // does prepending to the new target remove it from the old one?
+        // If not, should we fix that there, or here?
+        m_scaleTransform.prependToItem(target());
+        m_rotationTransform.prependToItem(target());
+    }
+}
+
+void QQuickPinchHandler::handlePointerEventImpl(QQuickPointerEvent *event)
+{
+    Q_UNUSED(event)
+
+    if (Q_UNLIKELY(lcPinchHandler().isDebugEnabled())) {
+        for (QQuickEventPoint *point : qAsConst(m_currentPoints))
+            qCDebug(lcPinchHandler) << point->state() << point->sceneGrabPos() << "->" << point->scenePos();
+    }
+
+    // TODO check m_pinchOrigin: right now it acts like it's set to PinchCenter
+    QPointF startCentroid = startingCentroid();
+    QPointF centroid = touchPointCentroid();
+    QVector3D origin(centroid);
+
+    qreal startDist = averageStartingDistance(startCentroid);
+    qreal dist = averageTouchPointDistance(centroid);
+    qreal zoom = dist / startDist;
+
+    qreal newScale = qBound(m_minimumScale, zoom * m_startScale, m_maximumScale);
+    m_scaleTransform.setOrigin(origin);
+    // TODO optionally allow separate x and y scaling?
+    m_scaleTransform.setXScale(newScale);
+    m_scaleTransform.setYScale(newScale);
+
+    qreal startAngle = averageStartingAngle(startCentroid);
+    qreal angle = averageTouchPointAngle(centroid);
+    qreal angleDelta = startAngle - angle;
+    m_rotationTransform.setOrigin(origin);
+    m_rotationTransform.setAngle(qMin(m_maximumRotation, qMax(m_minimumRotation, m_startRotation + angleDelta)));
+
+    // TODO some translation inadvertently happens; try to hold the chosen pinch origin in place
+
+    qCDebug(lcPinchHandler) << "startCentroid" << startCentroid << "centroid"  << centroid << "dist" << dist << "starting dist" << startDist
+                            << "zoom" << zoom << "startScale" << m_startScale << "startAngle" << startAngle << "angle" << angle
+                            << "scale" << scale() << "rotation" << rotation();
+
+    emit updated();
+}
+
+QT_END_NAMESPACE