Qt 鼠标拖动缩放

在Qt drag和drop基础上，实现QGraphicsItem的鼠标拖动缩放，效果如下：

 

如图所示，整个item由两个QGraphicsItem组成，item1用来显示主图片，item2用来显示移动光标。

先来看item2的实现，它实现的功能有显示和消失（鼠标移动到item周围显示，其他地方消失）、颜色改变（使用鼠标缩放时改变颜色）。

void CornerGrabber : : paint ( QPainter * painter ,
const QStyleOptionGraphicsItem * ,
QWidget * )
{
// fill the box with solid color, use sharp corners
_outterborderPen . setCapStyle ( Qt : : SquareCap );
_outterborderPen . setStyle ( Qt : : SolidLine );
painter - > setPen ( _outterborderPen );
 
 
QPointF topLeft ( 0 , 0 );
QPointF bottomRight ( _width , _height );
 
 
QRectF rect ( topLeft , bottomRight );
 
 
QBrush brush ( Qt : : SolidPattern );
brush . setColor ( _outterborderColor );
painter - > fillRect ( rect , brush );
}

 

item2其实是一个巨型，宽和高由_width和_height确定，颜色由_outterborderColor确定，初始时黑色。

void CornerGrabber : :hoverLeaveEvent( QGraphicsSceneHoverEvent * )
{
    _outterborderColor = Qt : :black;
     this - >update( 0, 0,_width,_height);
}
 
void CornerGrabber : :hoverEnterEvent( QGraphicsSceneHoverEvent * )
{
    _outterborderColor = Qt : :red;
     this - >update( 0, 0,_width,_height);
}

当进入item2的hover事件时，将_outterborderColor设置为红色，然后重新绘制，离开时再该回黑色。

 

void CornerGrabber : :mouseMoveEvent(QGraphicsSceneDragDropEvent *event)
{
    event - >setAccepted( false);
}
 
void CornerGrabber : :mousePressEvent(QGraphicsSceneDragDropEvent *event)
{
    event - >setAccepted( false);
}
 
void CornerGrabber : :mouseReleaseEvent( QGraphicsSceneMouseEvent * event )
{
    event - >setAccepted( true);
}
 
void CornerGrabber : :mousePressEvent( QGraphicsSceneMouseEvent * event )
{
    event - >setAccepted( false);
}
 
void CornerGrabber : :mouseMoveEvent( QGraphicsSceneMouseEvent * event )
{
    event - >setAccepted( false);
}

以上代码，表示item2自己处理mouseReleaseEvent事件（实际什么也不做），其他四种事件不处理。

 

下面看一下item1的实现。

void WorkspaceItem : :paint(QPainter *painter,
                           const QStyleOptionGraphicsItem *option,
                          QWidget *widget)
{
    Q_UNUSED(option)
    Q_UNUSED(widget)
    painter - >drawPixmap(BoundDelta, BoundDelta, pixmap_);
     if(isSelected())
    {
        painter - >setPen(Qt : :DashLine);
        painter - >drawRect(BoundDelta, BoundDelta, pixmap_width, pixmap_height);
    }
}

先绘制中间显示的图片，如果被选中绘制虚线轮廓。

 

void WorkspaceItem : :hoverEnterEvent(QGraphicsSceneHoverEvent *event)
{
    Q_UNUSED(event)
    corner = new CornerGrabber( this);
    corner - >installSceneEventFilter( this);
    updateCornerPosition();
}
 
void WorkspaceItem : :hoverLeaveEvent(QGraphicsSceneHoverEvent *event)
{
    Q_UNUSED(event)
     delete corner;
}

这里跟item2类似，但又一点注册事件过滤器，用来处理item2不处理的四种事件（处理方法见下面函数）。

 

bool WorkspaceItem : :sceneEventFilter(QGraphicsItem *watched, QEvent *event)
{
    CornerGrabber * corner = dynamic_cast <CornerGrabber * >(watched);
     if(corner == NULL)
         return false;
 
    QGraphicsSceneMouseEvent * mevent = dynamic_cast <QGraphicsSceneMouseEvent * >(event);
     if(mevent == NULL)
         return false;
 
     switch(event - >type())
    {
     case QEvent : :GraphicsSceneMousePress :
        corner - >setMouseState(CornerGrabber : :kMouseDown);
        corner - >mouseDownX = mevent - >pos().x();
        corner - >mouseDownY = mevent - >pos().y();
         break;
     case QEvent : :GraphicsSceneMouseRelease :
        corner - >setMouseState(CornerGrabber : :kMouseReleased);
         break;
     case QEvent : :GraphicsSceneMouseMove :
        corner - >setMouseState(CornerGrabber : :kMouseMoving );
         break;
     default :
         return false;
    }
 
     if(corner - >getMouseState() == CornerGrabber : :kMouseMoving)
    {
        qreal x = mevent - >pos().x(), y = mevent - >pos().y();
 
        qreal width = x - corner - >mouseDownX + pixmap_width;
        qreal height = y - corner - >mouseDownY + pixmap_height;
 
        QImage image;
         if(text == "Mark")
            image.load( ":/images/banner_mark.png");
         else
            image.load( ":/images/banner_text.png");
        QSize size = image.size();
         if(size.width() < pixmap_width || size.height() < pixmap_height)
        {
            width = size.width();
            height = size.height();
        }
        qreal xscale = width / size.width();
        qreal yscale = height / size.height();
 
        qreal scale = qMax(xscale,yscale);
 
        QMatrix matrix;
        matrix.scale(scale, scale);
        image = image.transformed(matrix);
        pixmap_ = QPixmap : :fromImage(image);
        pixmap_width = pixmap_.width();
        pixmap_height = pixmap_.height();
 
        updateCornerPosition();
        update();
        scene() - >update();
    }
     return true;
}

鼠标Press事件，记录鼠标位置

鼠标Move事件，如果数据左键是按下的，记录当前的位置，计算缩放后的大小和原先大小的比例，然后对图片按比例缩放

鼠标Release事件，什么多不做

 

以上是主要代码，完整源码：点击下载