来自图像的QPixmap导致分割错误

问题描述

| 我在这里完全不知所措... 我正在尝试将QImage转换为Qpixmap，但是我的程序始终由于以下堆栈跟踪而崩溃。奇怪的是，如果我指定的QRectF的左上角没有（0，0），那么它可以正常工作。我知道QImage也有一个复制方法，但是那也失败了（没有有用的stacktrace），所以我想我会尝试使用pixmaps代替... Line 4/5的stacktrace是我的，但我基本上是在做以下事情

QImage _drawing = QImage(1024,1024);
// fill _drawing with some data

QRect i_work = QRect(1,1,10,10);
QRect i_break = QRect(0,10);

Qpixmap foo = Qpixmap::fromImage(_drawing);
// Qpixmap good = foo.copy(i_work); // I work
Qpixmap broken = foo.copy(i_break); // Segmentation fault...

堆栈跟踪：

Program received signal SIGSEGV,Segmentation fault.
0x01f44024 in QBasicAtomicInt::ref (this=0xabababab)
    at ../../include/QtCore/../../src/corelib/arch/qatomic_i386.h:120
120     ../../include/QtCore/../../src/corelib/arch/qatomic_i386.h: No such file
 or directory.
        in ../../include/QtCore/../../src/corelib/arch/qatomic_i386.h
(gdb) bt
#0  0x01f44024 in QBasicAtomicInt::ref (this=0xabababab)
    at ../../include/QtCore/../../src/corelib/arch/qatomic_i386.h:120
#1  0x01964d3e in QImage::QImage (this=0x28cc70,image=...)
    at image\\qimage.cpp:1125
#2  0x01990682 in QRasterpixmapData::fromImage (this=0xc391a00,sourceImage=...,flags=...) at image\\qpixmap_raster.cpp:151
#3  0x019862ab in Qpixmap::fromImage (image=...,flags=...)
    at image\\qpixmap.cpp:2031
#4  0x00423fdc in TxImage::getSelection (this=0xc3b6cb0,selection_area=...)
    at TxImage.cpp:207
#5  0x004421e2 in RomView::mouseReleaseEvent (this=0xc397978,event=0x28d5fc)
    at RomView.cpp:261
#6  0x019241a0 in QWidget::event (this=0xc397978,event=0x28d5fc)
    at kernel\\qwidget.cpp:8187
#7  0x01c9e6bc in qframe::event (this=0xc397978,e=0x28d5fc)
    at widgets\\qframe.cpp:557
#8  0x01d2bf0f in QAbstractScrollArea::viewportEvent (this=0xc397978,e=0x28d5fc) at widgets\\qabstractscrollarea.cpp:1043
#9  0x01e9aae6 in QGraphicsView::viewportEvent (this=0xc397978,event=0x28d5fc) at graphicsview\\qgraphicsview.cpp:2862
#10 0x01f86a13 in QAbstractScrollAreaPrivate::viewportEvent (this=0xc3969f8,event=0x28d5fc) at widgets//qabstractscrollarea_p.h:100
#11 0x01f8506c in QAbstractScrollAreaFilter::eventFilter (this=0xbfa7388,o=
    0xbf43978,e=0x28d5fc) at widgets//qabstractscrollarea_p.h:116
#12 0x6a1ffc73 in QCoreApplicationPrivate::sendThroughObjectEventFilters (
    this=0xa7a46d8,receiver=0xbf43978,event=0x28d5fc)
    at kernel\\qcoreapplication.cpp:847
#13 0x018d96e5 in QApplicationPrivate::notify_helper (this=0xa7a46d8,e=0x28d5fc) at kernel\\qapplication.cpp:4392
#14 0x018d7909 in QApplication::notify (this=0x28fe34,e=0x28d5fc) at kernel\\qapplication.cpp:3959
#15 0x6a1ff9dc in QCoreApplication::notifyInternal (this=0x28fe34,event=0x28d5fc) at kernel\\qcoreapplication.cpp:732
#16 0x01f4d53e in QCoreApplication::sendSpontaneousEvent (receiver=0xbf43978,event=0x28d5fc)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#17 0x018d6118 in QApplicationPrivate::sendMouseEvent (receiver=0xbf43978,event=0x28d5fc,alienWidget=0xc3adb70,nativeWidget=0x28fd60,buttonDown=0x237941c,lastMouseReceiver=...,spontaneous=true)
    at kernel\\qapplication.cpp:3056
#18 0x0193fc63 in QETWidget::translateMouseEvent (this=0x28fd60,msg=...)
    at kernel\\qapplication_win.cpp:3317
#19 0x0193aaa6 in QtWndProc (hwnd=0x130fb8,message=514,wParam=0,lParam=5373956) at kernel\\qapplication_win.cpp:1657
#20 0x762c62fa in USER32!OffsetRect () from C:\\Windows\\syswow64\\user32.dll
#21 0x900010c2 in ?? ()
#22 0x90909090 in ?? ()
#23 0x00df7d80 in operator+ ()
Backtrace stopped: prevIoUs frame inner to this frame (corrupt stack?)
(gdb)

我向您保证qatomic_i386.h存在，并查看第120行...

112: inline bool QBasicAtomicInt::ref()
113: {
114:     unsigned char ret;
115:    asm volatile(\"lock\\n\"
116:                 \"incl %0\\n\"
117:                 \"setne %1\"
118:                 : \"=m\" (_q_value),\"=qm\" (ret)
119:                 : \"m\" (_q_value)
120:                 : \"memory\");
121:    return ret != 0;
122: }

    

解决方法

        很难说是怎么回事。但是QImage构造函数的QT Doc说   警告：这将创建一个QImage   与未初始化的数据。呼叫fill（）   用适当的图像填充图像   绘制之前的像素值   与QPainter。 通过调用fill（）方法确保QImage正确填充。也许这就是问题的原因。     ,        我能够成功解决问题，但是我不确定潜在的问题，因为该解决方法对我而言并没有多大意义。 所以我在

QGraphicsScene

/

QGraphicsView

上渲染

QImage

。我在场景中的位置（0,0）有

QImage

，在位置（0,0）处也有

QGraphicsItem

。在调用

QImage

上的副本之前，从场景中删除另一个

QGraphicsItem

似乎可以解决此问题。我不知道ѭ10点有何特别之处。我唯一想到的是

QPoint(0,0)

上的

isNull

返回

true

。