隐藏超出边界的 QGraphicsItem 区域 [英] Hide area of QGraphicsItem that is out of boundary

问题描述

我在 QGraphicsScene 中有一个 QGraphicsPixmap 项目.该项目的标志设置为 ItemIsMovable 和 ItemIsSelectable.我如何确保当项目移出某个边界时 - 它可以是 QGraphicsScene 或只是固定坐标处的固定帧大小 - 部分会隐藏?

I have a QGraphicsPixmap item in a QGraphicsScene. The item has flags set to ItemIsMovable, and ItemIsSelectable. How do I ensure that when the item is moved out of a certain boundary - it can be a QGraphicsScene or just a fixed frame size at fixed coordinates - the part becomes hidden?

例如.

篮球的左侧部分变得隐藏起来.

The left part of the basketball becomes hidden.

推荐答案

必须使用setClipPath().

在下面的代码中，我创建了一个继承自 QGraphicsPixmapItem 的类(对于继承自 QGraphicsItem 的其他类也是如此)，我创建了方法 setBoundaryPath() 接收指示可见区域的 QPainterPath，例如在代码中使用:

In the following code I have created a class that inherits from QGraphicsPixmapItem (the same could do with other classes that inherit from QGraphicsItem) and I created the method setBoundaryPath() that receives a QPainterPath that indicates the visible area, for example in the code use:

QPainterPath path;
path.addRect(QRectF(100, 100, 400, 200));

那个 QPainterPath 是一个矩形，其左上角是 QGraphicsScene 的点 (100, 100)，宽度为 400，200高度.

That QPainterPath is a rectangle whose topleft is the point (100, 100) of the QGraphicsScene with size of 400 in width and 200 in height.

#include <QApplication>
#include <QGraphicsRectItem>
#include <QGraphicsView>

class GraphicsPixmapItem: public QGraphicsPixmapItem{

public:
    GraphicsPixmapItem(const QPixmap & pixmap,  QGraphicsItem *parent = 0):
        QGraphicsPixmapItem(pixmap, parent)
    {
        setFlag(QGraphicsItem::ItemIsMovable, true);
        setFlag(QGraphicsItem::ItemIsSelectable, true);
    }
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){
        if(!m_boundaryPath.isEmpty()){
            QPainterPath path = mapFromScene(m_boundaryPath);
            if(!path.isEmpty())
                painter->setClipPath(path);
        }
        QGraphicsPixmapItem::paint(painter, option, widget);
    }

    QPainterPath boundaryPath() const{
        return m_boundaryPath;
    }
    void setBoundaryPath(const QPainterPath &boundaryPath){
        m_boundaryPath = boundaryPath;
        update();
    }

private:
    QPainterPath m_boundaryPath;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QGraphicsView view;
    QGraphicsScene scene(0, 0, 600, 400);
    view.setScene(&scene);
    view.setBackgroundBrush(QBrush(Qt::gray));

    GraphicsPixmapItem *p_item = new GraphicsPixmapItem(QPixmap(":/ball.png"));
    p_item->setPos(100, 100);

    // Define the area that will be visible
    QPainterPath path;
    path.addRect(QRectF(100, 100, 400, 200));

    p_item->setBoundaryPath(path);
    scene.addItem(p_item);

    // the item is added to visualize the intersection
    QGraphicsPathItem *path_item = scene.addPath(path, QPen(Qt::black), QBrush(Qt::white));
    path_item->setZValue(-1);
    view.show();
    return a.exec();
}

您可以在此链接中找到示例代码.

You can find the example code in this link.

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