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arrow.cpp
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/****************************************************************************
**
** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the examples of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** 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 Digia Plc and its Subsidiary(-ies) 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."
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include "arrow.h"
#include <math.h>
#include <QPen>
#include <QPainter>
const qreal Pi = 3.14;
//! [0]
// We set the start and end diagram items of the arrow. The arrow head will be drawn where the line intersects the end item.
Arrow::Arrow(DiagramItem *startItem, DiagramItem *endItem, QGraphicsItem *parent)
: QGraphicsLineItem(parent)
{
myStartItem = startItem;
myEndItem = endItem;
setFlag(QGraphicsItem::ItemIsSelectable, true);
myColor = Qt::black;
setPen(QPen(myColor, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
}
//! [0]
//! [1]
// We need to reimplement this function because the arrow is larger than the bounding rectangle of the QGraphicsLineItem. The graphics scene uses the bounding rectangle to know which regions of the scene to update.
QRectF Arrow::boundingRect() const
{
qreal extra = (pen().width() + 20) / 2.0;
return QRectF(line().p1(), QSizeF(line().p2().x() - line().p1().x(),
line().p2().y() - line().p1().y()))
.normalized()
.adjusted(-extra, -extra, extra, extra);
}
//! [1]
//! [2]
// The shape function returns a QPainterPath that is the exact shape of the item. The QGraphicsLineItem::shape() returns a path with a line drawn with the current pen, so we only need to add the arrow head. This function is used to check for collisions and selections with the mouse.
QPainterPath Arrow::shape() const
{
QPainterPath path = QGraphicsLineItem::shape();
path.addPolygon(arrowHead);
return path;
}
//! [2]
//! [3]
// This slot updates the arrow by setting the start and end points of its line to the center of the items it connects.
void Arrow::updatePosition()
{
QLineF line(mapFromItem(myStartItem, 0, 0), mapFromItem(myEndItem, 0, 0));
setLine(line);
}
//! [3]
//! [4]
// If the start and end items collide we do not draw the arrow; the algorithm we use to find the point the arrow should be drawn at may fail if the items collide.
void Arrow::paint(QPainter *painter, const QStyleOptionGraphicsItem *,
QWidget *)
{
if (myStartItem->collidesWithItem(myEndItem))
return;
QPen myPen = pen();
myPen.setColor(myColor);
qreal arrowSize = 20;
painter->setPen(myPen);
painter->setBrush(myColor);
//! [4] //! [5]
// We first set the pen and brush we will use for drawing the arrow.
QLineF centerLine(myStartItem->pos(), myEndItem->pos());
QPolygonF endPolygon = myEndItem->polygon();
QPointF p1 = endPolygon.first() + myEndItem->pos();
QPointF p2;
QPointF intersectPoint;
QLineF polyLine;
for (int i = 1; i < endPolygon.count(); ++i) {
p2 = endPolygon.at(i) + myEndItem->pos();
polyLine = QLineF(p1, p2);
QLineF::IntersectType intersectType =
polyLine.intersect(centerLine, &intersectPoint);
if (intersectType == QLineF::BoundedIntersection)
break;
p1 = p2;
}
setLine(QLineF(intersectPoint, myStartItem->pos()));
//! [5] //! [6]
// We then need to find the position at which to draw the arrowhead. The head should be drawn where the line and the end item intersects. This is done by taking the line between each point in the polygon and check if it intersects with the line of the arrow. Since the line start and end points are set to the center of the items the arrow line should intersect one and only one of the lines of the polygon. Note that the points in the polygon are relative to the local coordinate system of the item. We must therefore add the position of the end item to make the coordinates relative to the scene.
// We calculate the angle between the x-axis and the line of the arrow. We need to turn the arrow head to this angle so that it follows the direction of the arrow. If the angle is negative we must turn the direction of the arrow.
double angle = ::acos(line().dx() / line().length());
if (line().dy() >= 0)
angle = (Pi * 2) - angle;
QPointF arrowP1 = line().p1() + QPointF(sin(angle + Pi / 3) * arrowSize,
cos(angle + Pi / 3) * arrowSize);
QPointF arrowP2 = line().p1() + QPointF(sin(angle + Pi - Pi / 3) * arrowSize,
cos(angle + Pi - Pi / 3) * arrowSize);
arrowHead.clear();
arrowHead << line().p1() << arrowP1 << arrowP2;
//! [6] //! [7]
// We can then calculate the three points of the arrow head polygon. One of the points is the end of the line, which now is the intersection between the arrow line and the end polygon. Then we clear the arrowHead polygon from the previous calculated arrow head and set these new points.
painter->drawLine(line());
painter->drawPolygon(arrowHead);
// If the line is selected, we draw two dotted lines that are parallel with the line of the arrow. We do not use the default implementation, which uses boundingRect() because the QRect bounding rectangle is considerably larger than the line.
if (isSelected()) {
painter->setPen(QPen(myColor, 1, Qt::DashLine));
QLineF myLine = line();
myLine.translate(0, 4.0);
painter->drawLine(myLine);
myLine.translate(0,-8.0);
painter->drawLine(myLine);
}
}
//! [7]