QPainter begin Error

[Runner111]

I use QPainter in a thread to draw QImage. the Function run once is right. But in second time, at pait.begin(g_GE->GetDrawBuffer()) will error. The infomation is Signal Received windows, Signal name:SIGSEGV, Signal meaning: Segmentation fault.
The Debuger output is: QPainterPrivate::attachPainterPrivate(QPainter*, QPaintDevice*) error.
The code :
QRect target;
pait.begin(g_GE->GetDrawBuffer());
pait.setRenderHint(QPainter::Antialiasing, true);
g_GE->SetisDraw(true);
while(g_GE->GetImageArray()->size()) {
ImageInfo* pInfo = g_GE->GetImageArray()->at(0);
g_GE->GetImageArray()->pop_front();
if (pInfo->type == _gedraw) {
target = pInfo->rect;
pait.drawImage(target, *(pInfo->pImg), pInfo->rect);
}
}
pait.end();
g_GE->SetisDraw(false);
return 0;

Version is Qt 5.14.1 MinGW 7.3.0 32bit
OS:Windows 10

[Pl45m4]

@Runner111

Do you try to paint on the same image twice (from different threads)?

[Runner111]

No, I have only one thread.

[Runner111]

@Pl45m4 And I use pait.isActive(); to check the pait is idle now.

[jsulm]

@Runner111 said in QPainter begin Error:

g_GE

Is this a valid pointer when the code is executed second time?

[Runner111]

@jsulm Yes, it is a global object, because my project has some C interface, so use global object

[Runner111]

This post is deleted!

[Runner111]

@Runner111 said in QPainter begin Error:

qpainter

I try MSVC2015 the error is gone, but it will output
22:46:08: Debugging starts
QPainter::begin: A paint device can only be painted by one painter at a time.
QPainter::end: Painter not active, aborted
QPainter::begin: A paint device can only be painted by one painter at a time.
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setBackgroundMode: Painter not active
QPainter::end: Painter not active, aborted
QPainter::begin: A paint device can only be painted by one painter at a time.
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setBackgroundMode: Painter not active
QPainter::end: Painter not active, aborted

But the paintEvent in MainWindow, I already delete the code, it is a empty function, who call the QPainter?

[SGaist]

Hi,

Can you show the actual code you are using including function signature ?

[Runner111]

@SGaist The Project have many file, but I can explain the mathod. This project will read more RGB Data from Peripheral module, I use a thread to read the data, create a image, and then show on the mainwindow.

In mainwindow:

    ui->setupUi(this);
    g_GE = &m_GraphEngine;
    m_GraphEngine.InitGraphEngine(this);
    QUIThread* p = new QUIThread;
    p->start();

In mainwindow paintevent:

void MainWindow::paintEvent(QPaintEvent *e) {
}

I doubt the part will conflict with thread, so I delete it.
In Thread, because I need make some Interface for Peripheral module, some function write in C.

void GraphEngine::InitGraphEngine(MainWindow* w) {
    QFile file(".\\GraphConfig.ini");
    if (!file.open(QIODevice::ReadOnly)) {
        return;
    }

    QTextStream in(&file);
    QString info = file.readLine();
    m_width = info.right(info.length() - info.indexOf(":") - 1).toInt();
    info = file.readLine();
    m_height = info.right(info.length() - info.indexOf(":") - 1).toInt();
    file.close();
    m_DrawBuffer = new QImage(m_width, m_height, QImage::Format_ARGB32);
    m_BackBuffer = new QImage(m_width, m_height, QImage::Format_ARGB32);
    m_Window = w;
}

STHBITMAP STCreateBitmap(int nWidth, int nHeight, t_sgaColorFormat format, const void* lpvBits) {
    int i;
    unsigned long r;
    unsigned long g;
    unsigned long b;
    unsigned short* shortdata;
    unsigned long* longdata;
    unsigned char* pdata = new unsigned char[nWidth * nHeight * 4];

    shortdata = (unsigned short*)lpvBits;
    longdata = (unsigned long*)pdata;
    if (format.bufferFmt == SGA_PIX_FORMAT_RGB16) {        
        for (i = 0; i < nWidth * nHeight; i ++) {
            r = shortdata[i] >> 11;
            g = (shortdata[i] &0x7e0) >> 5;
            b = shortdata[i] & 0x1f;
            longdata[i] = 0xFF000000 | (r << 16) | (g << 8) | b;
        }
    }
    else if (format.bufferFmt == SGA_PIX_FORMAT_ARGB24){
        memcpy(pdata, lpvBits, nWidth * nHeight * 4);
    }
    QImage* pimage = new QImage(pdata, nWidth, nHeight, 4 * nWidth, QImage::Format_ARGB32);
    return (STHBITMAP)pimage;
}

int addImage( int x0, int ly0, int x1, int ly1, STHBITMAP pSrc, float nXSrc, int nYSrc, STROP dwRop) {
    ImageInfo* pInfo = new ImageInfo;
    pInfo->pImg = (QImage*)pSrc;
    pInfo->scissorrect.setX(g_GE->GetScissorX());
    pInfo->scissorrect.setY(g_GE->GetScissorY());
    pInfo->scissorrect.setWidth(g_GE->GetScissorW());
    pInfo->scissorrect.setHeight(g_GE->GetScissorH());
    pInfo->rect.setX(x0);
    pInfo->rect.setY(ly0);
    pInfo->rect.setWidth(x1 - x0);
    pInfo->rect.setHeight(ly1 - ly0);
    pInfo->type = _gedraw;
    g_GE->GetImageArray()->insert(g_GE->GetImageArray()->size(), pInfo);
    return 0;
}

int STFinish(STHDC hDC) {
#if 1
    QRect target;
    QPainter* pait = new QPainter;
    pait->begin(g_GE->GetDrawBuffer());
    pait->setRenderHint(QPainter::Antialiasing, true);
    pait->setBackgroundMode(Qt::TransparentMode);
    g_GE->SetisDraw(true);
    while(g_GE->GetImageArray()->size()) {
        ImageInfo* pInfo = g_GE->GetImageArray()->at(0);
        g_GE->GetImageArray()->pop_front();
        if (pInfo->type == _gedraw) {
            target = pInfo->rect;
            pait->drawImage(target, *(pInfo->pImg), pInfo->pImg->rect());
        }
}
    pait->end();
    delete pait;
    g_GE->SetisDraw(false);
#endif
    return 0;
}

[SGaist]

Taking a look at it, it seems you might be over-engineering some things.

Can you explain the C interface you are using ?
Is it something public that can be looked at ?
Why do you need that global object ?

[Runner111]

@SGaist Because I need use a device, its library is written by C. But I already fix this bug.
QImage need fill first.