Draw rectangle on QImage

[^NyAw^]

Hi,

I'm trying to draw a rectangle into a QImage using QPainter but I don't know what I'm doing wrong. This code is executed out of the paintEvent

QPainter qPainter(&qImage);
qPainter.setBrush(Qt::NoBrush);
qPainter.setPen(Qt::red);
qPainter.drawRect(iX,iY,iWidth,iHeight);
ui.imageLabel->setPixmap(QPixmap::fromImage(qImage));

QPainter qPainter(&qImage);
qPainter.setBrush(Qt::NoBrush);
qPainter.setPen(Qt::red);
qPainter.drawRect(iX,iY,iWidth,iHeight);
ui.imageLabel->setPixmap(QPixmap::fromImage(qImage));

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The image is showed but not the rectangle.
"iX,iY,iWidth,iHeight" have values into the image size.

Thanks,

[Viper666]

because you must at first set image and after that draw rectangle because you overflow your retangle with image

[^NyAw^]

Hi,

The image is readed before painting the rectangle

[wysota]

Try calling qPainter.end() before converting the image to a pixmap.

[^NyAw^]

Hi,

Try calling qPainter.end() before converting the image to a pixmap.

Same result. I've also tryied to save the image on disk after calling "qPainter.end()" but the image is the same as the input image.

Maybe there is a better way to do what I want:
I have an image loaded from a Database(the image is loaded correctly). The Database also returns me a position and dimension of a rectangle that I want to show over the image. The image is painted on a QLabel scaling it to fill the QLabel dimension(mantaining the aspect ratio of the image), so the position to paint the rectangle are different. This is why I want to paint the rectangle directly into the image before scaling the image.

Thanks,

[wysota]

Please provide some minmal compilable example reproducing the problem.

[^NyAw^]

Hi,

I've tried this code in the constructor of a simple program.

QImage qImage("a.bmp");
QPainter qPainter(&qImage);
qPainter.setBrush(Qt::NoBrush);
qPainter.setPen(Qt::red);
qPainter.drawRect(150,150,50,50);
bool bEnd = qPainter.end();
qImage.save("b.bmp");

QImage qImage("a.bmp");
QPainter qPainter(&qImage);
qPainter.setBrush(Qt::NoBrush);
qPainter.setPen(Qt::red);
qPainter.drawRect(150,150,50,50);
bool bEnd = qPainter.end();
qImage.save("b.bmp");

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With this I'll get the image "b.bmp" that is the same as "a.bmp" but with a red rectangle painted on position (150px,150px) with a widht and height of 50px.
This don't work as "b.bmp" is identical as "a.bmp"

Thanks,

[wysota]

What is the format of the BMP image? Is it 8b (indexed) or 24b (true color)?