c++ - QGraphicsItem 子类抛出 X 错误并崩溃

Question

我正在尝试创建一个 QGraphicsItem，它将以线程方式从文件中提取数据，并在读入数据时显示它。看代码:

#ifndef TILE_H
#define TILE_H

#include <QGraphicsItem>
#include <QThread>
#include <QFutureWatcher>
#include <QtConcurrentRun>
#include "gdal_priv.h"
#include <QPainter>

class Tile : public QObject, public QGraphicsItem
{
    Q_OBJECT
    Q_INTERFACES(QGraphicsItem)

public:
    Tile(QGraphicsItem *parent = 0);

    Tile( int nBlocksX, int nBlocksY, int xoffset, int yoffset, int nXBlockSize, int nYBlockSize, int A_BPP,QGraphicsItem *parent=0);
    ~Tile();
    void LoadTilePixmap();

protected:
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget);
    QRectF boundingRect() const;

private:
    QFutureWatcher<void> *watcher;
    QFuture<void> *future;
    QImage *image;
    const QStyleOptionGraphicsItem *TileOption;
    QPainter *TilePainter;
    QWidget *TileWidget;
    int nBlocksX, nBlocksY, nBlockXSize, nBlockYSize, tilePosX, tilePosY, A_BPP;

signals:

public slots:
    void updateSceneSlot();

};

#endif // TILE_H

还有.cpp

#include "tile.h"

Tile::Tile(QGraphicsItem *parent) : QGraphicsItem(parent)
{
}

Tile::~Tile()
{
}
Tile::Tile(int nBlocksX, int nBlocksY, int xoffset, int yoffset, int nXBlockSize, int nYBlockSize, int A_BPP,QGraphicsItem *parent)
    : QGraphicsItem(parent)
{
//set some flags and size parameters related to reading from the file on disk. All instances of this QGraphicsItem read from the same file
    this->nBlocksX = nBlocksX;
    this->nBlocksY = nBlocksY;
    this->nBlockXSize = nXBlockSize;
    this->nBlockYSize = nYBlockSize;
    this->tilePosX =xoffset;
    this->tilePosY = yoffset;
    this->A_BPP = A_BPP;
    setCacheMode(NoCache);
    setFlag(QGraphicsItem::ItemIsMovable,false);
    setActive(true);
    this->setAcceptHoverEvents(true);
    this->setFlag(QGraphicsItem::ItemIsFocusable);
    this->image = NULL;

    this->future = new QFuture<void>;
    this->watcher = new QFutureWatcher<void>;
    connect(watcher,SIGNAL(finished()),this,SLOT(updateSceneSlot()));
}
QRectF Tile::boundingRect() const
{
    if(image == NULL)
        return(QRectF(0,0,0,0));

    return(QRectF(0,0,image->width(),image->height()));
}

void Tile::updateSceneSlot()
{
    qDebug("updateSceneSlot Thread id %i", QThread::currentThread());
    this->paint(TilePainter, TileOption, TileWidget);
}

void Tile::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget)
{
    if(image==NULL)
    {
        TilePainter=painter;
        TileOption=option;
        TileWidget=widget;
        qDebug()<<"Paint Thread id "<< QThread::currentThread();
        *future=QtConcurrent::run(this, &Tile::LoadTilePixmap);
        watcher->setFuture(*future);

    }

    QPointF *p = new QPointF(0.0,0.0);
    painter->drawImage(*p, *image);
}

void Tile::LoadTilePixmap()
{
 /*...populate floatData with data from file...*/

    image = new QImage(nXSize, nYSize, QImage::Format_RGB32);
        for (int i = 0 ; i < nYSize ; i++)
        {
             for (int j = 0 ; j < nXSize ; j++)
             {
                    image->setPixel(j,i,qRgb((unsigned char)floatData[i*nXSize+j],(unsigned char)floatData[i*nXSize+j],(unsigned char)floatData[i*nXSize+j]));
             }
         }


}

这可以正常编译，但是当我尝试加载图像时，出现一大堆 X 错误，然后程序退出:

.
.
.
X Error: BadGC (invalid GC parameter) 13
  Major opcode: 60 (X_FreeGC)
  Resource id:  0x1c002bb
X Error: RenderBadPicture (invalid Picture parameter) 181
  Extension:    156 (RENDER)
  Minor opcode: 7 (RenderFreePicture)
  Resource id:  0x1c002ba
X Error: BadPixmap (invalid Pixmap parameter) 4
  Major opcode: 54 (X_FreePixmap)
  Resource id:  0x1c002b9
X Error: BadAlloc (insufficient resources for operation) 11
  Major opcode: 53 (X_CreatePixmap)
  Resource id:  0x1c002bc
X Error: BadDrawable (invalid Pixmap or Window parameter) 9
  Extension:    156 (RENDER)
  Minor opcode: 4 (RenderCreatePicture)
  Resource id:  0x1c002bc
X Error: BadDrawable (invalid Pixmap or Window parameter) 9
  Major opcode: 55 (X_CreateGC)
  Resource id:  0x1c002bc
X Error: BadGC (invalid GC parameter) 13
  Major opcode: 56 (X_ChangeGC)
  Resource id:  0x1c002be
X Error: BadDrawable (invalid Pixmap or Window parameter) 9
  Major opcode: 70 (X_PolyFillRectangle)
  Resource id:  0x1c002bc
X Error: BadGC (invalid GC parameter) 13
  Major opcode: 60 (X_FreeGC)
  Resource id:  0x1c002be
X Error: RenderBadPicture (invalid Picture parameter) 181
  Extension:    156 (RENDER)
  Minor opcode: 7 (RenderFreePicture)
  Resource id:  0x1c002bd
X Error: BadPixmap (invalid Pixmap parameter) 4
  Major opcode: 54 (X_FreePixmap)
  Resource id:  0x1c002bc
Paint Thread id  QThread(0x105feac0) 
The program has unexpectedly finished.

我做错了什么？当我将此设置为单线程时，我能够毫无问题地执行此操作。

Answer 1

您的图像加载代码不是线程安全的，因为 QImage 不是线程安全的。这应该是您崩溃的原因。

您也有泄漏，例如在 paint() 中在堆上创建且从未删除的 QPoint。只需在堆栈而不是堆上创建它。图像也一样:你泄露了它，也不需要在堆上创建 QImage。 (它们是隐式共享的，因此拷贝很便宜)。