[Solved] Problem with QLabel, QPixmap and PaintEvent

[kamilus]

I have my own Widget called FrameWidget and in this widget i have a label in which i display QPixmap.
The first problem is that at the begining the label is black and i don't know why.
The second problem is when i call paintEvent function everything is drawed under my label ;/

When i put in my code @QPainter painter(label);@ the compilator show me:
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::setPen: Painter not active
QPainter::setBrush: Painter not active
QPainter::drawRects: Painter not active

Can someone help me with this?

my widget:
@
FrameWidget::FrameWidget(QWidget *parent) :
QWidget(parent)
{
layout = new QVBoxLayout;
label = new QLabel;
layout->setContentsMargins(10,10,10,10);
layout->addWidget(label);

QImage temp(640,480,QImage::Format_RGB32);
frame = temp;       

QPixmap obraz = QPixmap::fromImage(frame);
label->setPixmap(obraz);

setLayout(layout);

}@

@
void FrameWidget::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.setPen(QPen(Qt::black, 12, Qt::SolidLine, Qt::RoundCap));
painter.setBrush(QBrush(Qt::green, Qt::SolidPattern));
painter.drawRect(0,0, 300, 300);
}@

[yshurik]

That's not right to paint not on this in paintEvent of the object.
If you would like to have painter of label it should be paintEvent of the label

[kamilus]

can You give me an example how i can do this ?? I understand what You said, but i still don't know how to do this, i can't write sth like this:

@
void label::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.setPen(QPen(Qt::black, 12, Qt::SolidLine, Qt::RoundCap));
painter.setBrush(QBrush(Qt::green, Qt::SolidPattern));
painter.drawRect(0,0, 300, 300);
}@

[yshurik]

You are painting in label, so you need to subclass it:
class MyLabel : public QLabel { ... };
You need instantiate correct object in FrameWidget:
label = new MyLabel;
And then surely implement MyLabel::paintEvent(...) where you do your own painting on this (which is now MyLabel instance - what you needed)

[kamilus]

thanx a lot for Your help, i do this and it's work, but my problem is a little bit complicated, I want to have in this label an image from camera i have frames as a QPixmap, and I want to have four markers (2 horizontal and 2 vertical) on this QPixmap and i would like to move this markers.

After I implemented function @void myLabel::paintEvent(QPaintEvent *e){...}@ the frames from my camera don't show in myLabel. Can you help me with this?

[yshurik]

Do you paint these frames in paintEvent?
If not then there is no one who paint it.

Is it painted by superclass QLabel? - then inside of your paintEvent() you need to call QLabel::paintEvent before your paintings (they will go to top).

[kamilus]

it's my function to show frames from camera in myLabel
@
void FrameWidget::putFrame(IplImage *cvFrame){

switch(cvFrame->depth){
case IPL_DEPTH_8U:
    switch (cvFrame->nChannels){
    case 3:
        frame = QImage((const uchar *)cvFrame->imageData, cvFrame->width, cvFrame->height, QImage::Format_RGB888).rgbSwapped();
    break;

    default:
    QMessageBox msgBox;
    msgBox.setText("Wrong number of channels");
    msgBox.exec();
    break;
    }
 break;

 default:
 QMessageBox msgBox;
 msgBox.setText("This type of image is not implemented");
 msgBox.exec();
 break;
 }
label->setPixmap(QPixmap::fromImage(frame));  // its myLabel *label = new myLabel;

}@

[kamilus]

it's work, once again thank You, You help me a lot

[quote author="yshurik" date="1306611173"]Do you paint these frames in paintEvent?
If not then there is no one who paint it.

Is it painted by superclass QLabel? - then inside of your paintEvent() you need to call QLabel::paintEvent before your paintings (they will go to top).[/quote]