uchar* QImage::bits() returned '\0'...(nullptr)

[shtomik]

Hi to all guys,

Today, I'm trying to represent QImage as AVFrame(ffmpeg API).

// localImage is RGB32 QImage that fetching in func
QImage *img = new QImage(localImage);
if (!img->isNull()) {
    uchar* bits = img->bits();
}

But bits() func always return null, my uchar* pointer in debug always 0 or '\0'... What's wrong?

Thanks so much for your attention!

[mrjj]

Hi
What is localImage ? ( Type )

[shtomik]

@mrjj Hi, thanks for your reply :) Format_RGB32

[mrjj]

@shtomik
So its from
QImage QOpenGLWidget::grabFramebuffer() ?
Did you check what
http://doc.qt.io/qt-5/qimage.html#isNull
says ?
Also, do you do something like
https://stackoverflow.com/questions/13088749/efficient-conversion-of-avframe-to-qimage

[shtomik]

@mrjj

So its from
QImage QOpenGLWidget::grabFramebuffer() ?

Yes.

Did you check what
http://doc.qt.io/qt-5/qimage.html#isNull
says ?

Yea, what's wrong? In debug mode I saw that image is 1280x720 and with data...

Also, do you do something like
https://stackoverflow.com/questions/13088749/efficient-conversion-of-avframe-to-qimage

I read it, but I want to "convert" from QImage to AVFrame, not to QImage... I had a code for "converting" without data copy, but QImage::bits() func returned not correct pointer? If need to list code for converting, I can paste it, but is it correct way to think that my trouble really in bits() func? Thanks!

[mrjj]

@shtomik
Hi
ok so localImage is valid ?
Normally its due to invalid image it returns null.
But if in Format_RGB32 it should work.
localImage bits() also returns null ?

[shtomik]

@mrjj

ok so localImage is valid ?
localImage bits() also returns null ?

localImage and img I can to QImage::save(QStrings path ...), and it's work... So I think valid... 1 minute, please, I check it in debug. Thanks again ;)

[shtomik]

@mrjj
Yes, is valid, I can save pic and not null... All is good, but what's wrong?(

Now I'm using:

QImage *img = new QImage(ui->oGLArea->grabFramebuffer());

without localImage...

[mrjj]

So
After copying QImage to QImage, bits() fail ?
QImage::QImage(const QImage &image)
makes a shallow copy so i wonder if something goes out of scope ?
If you do
QImage img = ui->oGLArea->grabFramebuffer();
is bits() still NULL ?
Im wondering of the implicit sharing is doing something.

[shtomik]

@mrjj
I'm trying QImage::copy() too, but it's fail...

If you do
QImage img = ui->oGLArea->grabFramebuffer();
is bits() still NULL ?

Yes.

[mrjj]

@shtomik
Hmm. that is really odd if u can save them as working files.
Im out of guesses.
Give it some hours , others will come online and might have a good idea.

[shtomik]

@mrjj
thank you so much for your time and replies! I'm here... :)

[VRonin]

what does qDebug() << QByteArray(reinterpret_cast<const char*>(img->constBits()),img->bytesPerLine()).size(); print out (if it doesn't crash)?

[mranger90]

Are you sure its null ? By that I mean, what happens if you test

  if ( bits == nullptr ) {
   }
else {
     qDebug () << *bits << *(bits + 1) << *(bits + 2)
 }

I ask because your description of whats shown in the debuggers sounds like the
debugger is looking at the first part of the pixel, which could be 0.

[shtomik]

@VRonin
It doesn't crash o_O
5120 - output

[shtomik]

@mranger90
You are right! If first pixel not BLACK, debuger shows buffer of bits, but if first char - 0, empty buffer...

[shtomik]

@mranger90 @VRonin @mrjj

Thank you guys... I found a couple of mistakes in my code, but the main mistake was in trust to the debugger, sometimes it was 0x0 or 0 or '\0' value for pointer to uchar that was 0.