QLabel show image and drawLine

leafjungle

I want to draw a line in a image, and I am using QLabel.

first:
ui.mylabel->setPixmap(QPixmap::fromImage(img1));//display an image

second:
void paintEvent(QPaintEvent* ev){//override the paintEvent of Main Window

 QPainter draw(this);
 draw.drawLine(100, 100, 200,200);

}

But the line cannot be shown, because it is covered by the image.
The image should be a background for mylabel, and the line should be in the top layer.

How can I solve the problem?

p3c0

Hi,
Have you subclassed QLabel and reimplemented paintevent() ?

If so, then you must first drawPixmap first and then drawLine to make it overlap.

leafjungle

Is there any other solutions? I have reimplemented the paintEvent of the main windows, which contains a label.

[quote author="p3c0" date="1381121484"]Hi,
Have you subclassed QLabel and reimplemented paintevent() ?

If so, then you must first drawPixmap first and then drawLine to make it overlap.[/quote]

p3c0

What do you exactly want to do ? Can you elaborate more ?

So far i understood is
You have a QMainWindow whose paintEvent you have reimplemented(not a good idea) then it has a QLabel which you have added in your form and on which you want to draw the line ?

raven-worx

[quote author="leafjungle" date="1381125023"]Is there any other solutions? I have reimplemented the paintEvent of the main windows, which contains a label.[/quote]

That's not how it works. Each widget just draws it's own contents, but not it's child widgets. Child widgets are stacked on top and draw it's own contents, and so on...

leafjungle

Yes.

What I want is:
put an image on the QMainWindow, then draw a line on the image.

And the problem is:
The line is covered by the image, thus I can only see the image, the line is not visible.

[quote author="p3c0" date="1381125914"]What do you exactly want to do ? Can you elaborate more ?

So far i understood is
You have a QMainWindow whose paintEvent you have reimplemented(not a good idea) then it has a QLabel which you have added in your form and on which you want to draw the line ?[/quote]

leafjungle

I understand your points.

But if I want to put an image on the QMainWindow, then draw line on the QMainWindow. How can I make the line on top layer to make sure that it will not be covered by the image.

[quote author="raven-worx" date="1381127103"][quote author="leafjungle" date="1381125023"]Is there any other solutions? I have reimplemented the paintEvent of the main windows, which contains a label.[/quote]

That's not how it works. Each widget just draws it's own contents, but not it's child widgets. Child widgets are stacked on top and draw it's own contents, and so on...
[/quote]

leafjungle

!http://c.hiphotos.baidu.com/album/w=2048;q=90/sign=27d2541638f33a879e6d071af2642b49/d31b0ef41bd5ad6e2f2fb3cc83cb39dbb7fd3cc6.jpg(image1)!
http://f.hiphotos.bdimg.com/album/s=1400;q=90/sign=bc133aefd52a60595610e51e18040fea/d53f8794a4c27d1e3f07ede219d5ad6eddc438f7.jpg

!http://f.hiphotos.baidu.com/album/w=2048;q=90/sign=b6a92afc17ce36d3a20484300ecb01f6/d53f8794a4c27d1e3f07ede219d5ad6eddc438f7.jpg(image2)!
http://c.hiphotos.baidu.com/album/w=2048;q=90/sign=27d2541638f33a879e6d071af2642b49/d31b0ef41bd5ad6e2f2fb3cc83cb39dbb7fd3cc6.jpg

Look at the image above. what I want is image1, but the problem is shown in image2.

[quote author="raven-worx" date="1381127103"][quote author="leafjungle" date="1381125023"]Is there any other solutions? I have reimplemented the paintEvent of the main windows, which contains a label.[/quote]

That's not how it works. Each widget just draws it's own contents, but not it's child widgets. Child widgets are stacked on top and draw it's own contents, and so on...
[/quote]

leafjungle

http://f.hiphotos.bdimg.com/album/s=1400;q=90/sign=bc133aefd52a60595610e51e18040fea/d53f8794a4c27d1e3f07ede219d5ad6eddc438f7.jpg

http://c.hiphotos.baidu.com/album/w=2048;q=90/sign=27d2541638f33a879e6d071af2642b49/d31b0ef41bd5ad6e2f2fb3cc83cb39dbb7fd3cc6.jpg

p3c0

hi,

Both seems to be identical images. Can't see the problem.

jakakishan

if you First draw line and then set image then it may be solve.
sorry for poor eng.

ChrisW67

If you want the label to have the image with a line drawn on top then it is the paintEvent() of the QLabel you want to enhance.
@
class MyLabelSubclass: public QLabel {
...
protected:
void paintEvent(QPaintEvent* ev);
};

//override the paintEvent of QLabel to draw a line
void MyLabelSubclass::paintEvent(QPaintEvent* ev) {
QLabel::paintEvent(ev); // do the default label display

QPainter draw(this);
draw.setPen(QPen(QColor(Qt::red)));
draw.drawLine(rect().topLeft(), rect().bottomRight());
}
@
Then use MyLabelSubclass on the form rather than a base QLabel.

leafjungle

In the second image, a part of the line is covered by the image.

[quote author="p3c0" date="1382158070"]hi,

Both seems to be identical images. Can't see the problem.[/quote]

ChrisW67

There is no "In the second image, a part of the line is covered by the image," because there is no "part of the line" visible in the second. The two images above are byte for byte identical.
@
chrisw@newton /tmp $ md5sum *jpg
1b4061d36b2069e2956457d51fc6d3ad d31b0ef41bd5ad6e2f2fb3cc83cb39dbb7fd3cc6.jpg
1b4061d36b2069e2956457d51fc6d3ad d53f8794a4c27d1e3f07ede219d5ad6eddc438f7.jpg
@