qt 5.5.1 can't display in linuxfb:fb1

sheeran

I recently wrote a QT program to embed Linux with two buffer frames: dev / fb0 and dev / FB1

Through export QT_ QPA_ PLATFORM= linuxfb:fb=/dev/fb0 |1 control output

It is found that the program can output to fb0, but not to FB1

QT version is 5.5.1, which God can help me

SGaist

Hi and welcome to devnet,

Which device is that ?
Do you mean that if you force the frame buffer to 1 it does not work ?
What exact line do you use when it fails ?
Do you get any error message ?
Is there anything in the system logs with regard to that ?
Do you have any other application that can output on the second frame buffer ?
Are you locked to that outdated version of Qt ?

sheeran

@SGaist said in qt 5.5.1 can't display in linuxfb:fb1:

Hi and welcome to devnet,
Which device is that ?
Do you mean that if you force the frame buffer to 1 it does not work ?
What exact line do you use when it fails ?
Do you get any error message ?
Is there anything in the system logs with regard to that ?
Do you have any other application that can output on the second frame buffer ?
Are you locked to that outdated version of Qt ?

Hi SGaist:
This is a Linux device

Yes, the program doesn't work when I specify / dev / fb1 as the buffer frame

Error message:

QPainter::begin: Paint device returned engine == 0, type:0/1/2/3...

In addition, the program will directly terminate and find the segment error in QT source code:

qtbase/src/widgets/kernel/qwidget.cpp:

void QWidgetPrivate::setSystemClip(QPaintDevice *paintDevice, const QRegion &region)

{

// Transform the system clip region from device-independent pixels to device pixels

QPaintEngine *paintEngine = paintDevice->paintEngine();

QTransform scaleTransform;

const qreal devicePixelRatio = paintDevice->devicePixelRatio();

scaleTransform.scale (devicePixelRatio, devicePixelRatio);

paintEngine->d_ func()->systemClip = scaleTransform.map (region);

}

It is found that paintdevice > paintengine() is NULL in log printing

The QT version I use is determined to be 5.5.1, which means that this situation only occurs when fb1 is specified

I also confirm that the buffer frame of fb1 works

SGaist

Does it have the same properties as fb0 ?
How do you ensure that it works ?

sheeran

@SGaist
I'm sorry I didn't reply these days, because I'm busy with other things

I can make sure it works because it can run non QT programs

SGaist

You didn't answer about the differences between the devices behind fb0 and fb1.

What application do you run to test fb1 ?

sheeran

@SGaist
In the picture is the corresponding relationship between fb0 and fb1 and the device,
my qt program can only be output to the display screen,and when i :
cat test.yuv > /dev/fb1 : lcd can display this YUV picture ,so i confirm /dev/fb1 works.

SGaist

That's not a graphic application making use of fb1.
My question was rather: do you have any other graphical application able to access fb1 ?

sheeran

@SGaist QT version 4.7.3 program can run on fb1:
Through export QWS_DISPLAY= :/dev/fb1
When executing the program: xx -qws
fb1 is a virtual frame buffer

SGaist

Good.

Would it be possible to use a more recent version of Qt ?
5.5.1 is really out dated and the backend has likely changed since then.

In any case, I would add some debugging info to the plugin to determine what is happening. It could be some detection failing.