How do I use paintEvent to paint a QImage from video data? - c++

Question

I construct a QImage with data I get from an API call. This QImage I will draw with the overridden paintEvent(QPaintEvent*) method into a widget. From the function that does the API call I emit a signal that sends the grabbed data to a slot that constructs the QImage. With this process there is no problem. The data is transfered and the construct of the image works.
My question is how can I use the constucted image in the overridden paintEvent? I can open a image from the disk and draw it into the widget, but this works from inside the paintEvent() method. With the API call I got the data from outside.
class GrabberClass : public QObject
{
Q_OBJECT
public:
GrabberClass(QObject* parent = nullptr);
virtual ~GrabberClass();
bool applyFrameCallback();
bool getFrameData(DtMxData* data);
bool startProcessing();
private:
RenderClass *m_renderClass;
DtMxProcess *m_process;
DTAPI_RESULT m_result;
DtFrame *m_Frame
signals:
void sendFrameData(uchar* pData, int width, int height, int bytesPerRow);
};
//GrabberClass.cpp
//constructor
GrabberClass::GrabberClass(QObject *parent) :
m_renderClass(new RenderClass)
{
const bool connected = QObject::connect(this, &GrabberClass::sendFrameData, m_renderClass, &RenderClass::receiveFrameData, Qt::DirectConnection);
Q_ASSERT(connected); //value is true.
}
bool GrabberClass::applyFrameCallback()
{
auto frameCallback = [](DataContainer* frameData, void* pContext)
{
((GrabberClass*)pContext)->getFrameData(frameData);
};
m_result = m_process->AddMatrixCbFunc(frameCallback, this);
if (m_result != DTAPI_OK) {
return false;
}
return true;
}
bool GrabberClass::grabFrame(DataContainer* frameData)
{
m_Frame = frameData->m_Rows[IN_ROW].m_CurFrame;
uchar* pData = m_Frame->m_Video->m_Planes->m_pBuf;
int bytesPerRow = m_Frame->m_Video->m_Planes->m_Stride;
int frameWidth = m_Frame->m_Video->m_Width;
int frameHeight = m_Frame->m_Video->m_Height;
emit sendFrameData(pData, frameWidth, frameHeight, bytesPerRow);
return true;
}
//Render Class.h
class RenderClass : public QOpenGLWidget {
Q_OBJECT
public:
RenderClass(QWidget* parent = nullptr);
virtual ~RenderClass();
private:
QImage m_srcImage;
protected:
void paintEvent(QPaintEvent*);
public slots:
void receiveFrameData(uchar* pData, int width, int height, int bytesPerRow);
};
//RenderClass.cpp
VideoMonitor::VideoMonitor(QWidget* parent) :
QOpenGLWidget(parent),
m_srcImage(nullptr)
{
}
void RenderClass::receiveFrameData(uchar* pData, int width, int height, int bytesPerRow)
{
m_srcImage = QImage(pData, width, height, bytesPerRow, QImage::Format_Indexed8);
qDebug() << "Slot is called." << m_srcImage; //QImage is constructed with valid data
QWidget::update();
}
void RenderClass::paintEvent(QPaintEvent*)
{
if (!m_srcImage.isNull()) { //m_srcImage is null
QPainter painter(this);
painter.drawImage(this->rect(), m_srcImage);
painter.end();
qDebug() << "Draw image.";
}
else {
qDebug() << "QImage is null";
}
}
I'am new to C++, so it would be nice if someone of you can give me an advice and explaination.