自定义QGraphicItem和重绘问题 [英] Custom QGraphicItem and Repaint Issues

问题描述

全部，我实现了一个多边形的QGraphicsItem。然而，我现在在 update（）中遇到困难，因此我使用 QGraphicsEllipseItem c $ c>功能。我的代码发布在结尾，我的问题是：

1. 我在这里采取正确的方法吗？我开始怀疑自己


2. 我应该在我的实现中调用 QGraphicsItem :: update（）我称之为

其他一些信息：

• 我做了一个脏的小黑客。在我的实际代码中，我还继承了 QObject 。这允许我在场景（）（我知道已经使用 itemChange ）设置 eventFilter 。从场景中我在鼠标移动期间过滤 QGraphicsSceneMouseEvent 并且调用 QGraphicsItem :: update（）否则我的行不会


• 当我从场景中删除我的 InteractivePolygon 时，我的行不会被删除！我必须调用scene（） - > update。我觉得有点不对。

---

声明：

  class InteractivePolygon：public QGraphicsItem 
 {
 
 public：
 //只有重要的方法
 QRectF boundingRect（）const; 
 void paint（bla bla bla）; 
 bool eventFilter（QObject *，QEvent *）; 
 
 private：
 QList< QGraphicsEllipseItem *> m_points; 
 
 void AddPolygonPoint（QPointF）; 
 QGraphicsEllipseItem * MakeNewPoint（QPointF）; 
} 
  

实施：

  QRectF InteractivePolygon :: boundingRect（）const 
 {
 return childrenBoundingRect（）; 
} 
 
 void InteractivePolygon :: paint（QPainter painter .. otherstuf）
 {
 QPen line_pen（QColor（255,0,0））; 
 painter-> setPen（line_pen）; 
 
 if（m_points.count（）> 1）
 {
 for（int i = 1; i  painter-> drawLine（m_points [i-1]  - > pos（），m_points [i]  - > pos（））; 
} 
} 
 
 void AddPolygonPoint（QRectF point）
 {
 QGraphicsEllipseItem * new_item = MakeNewPoint（point）; 
 new_item-> setParent（this）; 
 
 m_points-> push_front（new_item）; 
 
 update（）; 
} 
 
 QGraphicsEllipseItem * InteractivePolygon :: MakeNewPoint（QPointF& new_point）
 {
 QGraphicsEllipseItem * result = 0; 
 result = new QGraphicsEllipseItem（）; 
 result-> setPos（new_point）; 
 result-> setRect（-4，-4，8，8）; 
 result-> setFlags（QGraphicsItem :: ItemIsMovable | QGraphicsItem :: ItemIsSelectable）
 
 return result; 
} 
 
 //假设这个方法正确设置/存在
 bool InteractivePolygon :: eventFilter（QObject * object，QEvent * event）
 {
 if（event-> type（）== QEvent :: QEvent :: GraphicsSceneMouseMove）
 {
 QGraphicsSceneMouseEvent * mouse_move =（QGraphicsSceneMouseEvent *）event; 
 //所选索引设置为else，让我们假设它工作
 if（selected_index）
 {
 update（）; //如果我不这样做，我的paint（）中的行不重绘。 
} 
} 
} 
  

解决方案>

解决方案是 prepareGeometryChange（）每次我改变任何东西，我的项目，将改变其边界框。

这允许我删除所有 update（）调用。 p>

All, I implemented a QGraphicsItem which is a polygon. I sped up development by using QGraphicsEllipseItem as the points (for the dragging capabilities.) However, I am now having difficulty in update() functionality. My code is posted at the end, my questions are:

1. Am I taking the right approach here? I am starting to doubt myself
2. Am I supposed to be calling QGraphicsItem::update() in my implementation? I call it alot

Some other info:

• I did a dirty little hack. In my actual code I also inherit from QObject. This allows me to install an eventFilter on the scene() (which I know has been set using itemChange). From the scene I filter QGraphicsSceneMouseEvent during mouse moves and call QGraphicsItem::update() otherwise my lines wouldn't be redrawn.
• When I remove my InteractivePolygon from the scene now, my lines are not removed! I have to call scene()->update. I feel like something's not right.

---

declaration:

class InteractivePolygon : public QGraphicsItem
{

public:
   //Only important methods
   QRectF boundingRect() const;
   void paint(bla bla bla);
   bool eventFilter(QObject *, QEvent *);

private:
   QList<QGraphicsEllipseItem *> m_points;

   void AddPolygonPoint(QPointF);
   QGraphicsEllipseItem * MakeNewPoint(QPointF);
}

implementation:

QRectF InteractivePolygon::boundingRect() const
{
   return childrenBoundingRect();
}

void InteractivePolygon::paint(QPainter painter.. otherstuf)
{
   QPen line_pen(QColor(255,0,0));
   painter->setPen(line_pen);

   if(m_points.count() > 1)
   {
      for(int i = 1; i < m_points.count(); ++i)
          painter->drawLine(m_points[i-1]->pos(), m_points[i]->pos());
   }
}

void AddPolygonPoint(QRectF point)
{
   QGraphicsEllipseItem * new_item = MakeNewPoint(point);
   new_item->setParent(this);

   m_points->push_front(new_item);

   update();  
}

QGraphicsEllipseItem * InteractivePolygon::MakeNewPoint(QPointF & new_point)
{
   QGraphicsEllipseItem * result = 0;
   result = new QGraphicsEllipseItem();
   result->setPos(new_point);
   result->setRect(-4, -4, 8, 8);
   result->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable)

   return result;
}

//Lets pretend this method is correctly setup/exists
bool InteractivePolygon::eventFilter(QObject *object, QEvent *event)
{
   if(event->type() == QEvent::QEvent::GraphicsSceneMouseMove)
   {
      QGraphicsSceneMouseEvent * mouse_move = (QGraphicsSceneMouseEvent *)event;
      //Selected index is set else, let's assume it works
      if(selected_index)
      {
         update(); //If I don't do this, my lines in my paint() are not redrawn.
      }
   }
}

解决方案

The solution was prepareGeometryChange() everytime I changed anything in my item that would change its bounding box. Everything is redrawn correctly and updated as necessary.

This allowed me to remove all update() calls.

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