Qt5 linuxfb platform plugin does not work with 8bit color depth

Meyton_GmbH 0

I have ported an embedded application from Qtopia 4 to Qt 5. The Qt 4 application was running on linux framebuffer. The embedded device the application should run on uses the vesafb framebuffer driver. As I understand Qt 5 uses plugins to support different graphic plaforms (like linuxfb and X11). So I'm trying to run the ported application with the linuxfb framebuffer plugin.

./myApp -platform linuxfb

My problem now is that the ported application runs fine on machines with at least 16bit color depth. But I have to support old hardware which only supports 8bit color depth. On these devices the application starts, but produces no graphical output at all. On colsole I get the following errors:

QPainter::begin: Paint device returned engine == 0, type: 2
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setCompositionMode: Painter not active
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setCompositionMode: Painter not active
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
...

fbset gives the following output on the machine where the graphics do not work:

mode "1024x768-60"
    # D: 63.500 MHz, H: 47.816 kHz, V: 59.920 Hz
    geometry 1024 768 1024 768 8
    timings 15748 152 48 23 3 104 4
    vsync high
    rgba 8/0,8/0,8/0,0/0
endmode

Can it be that the linuxfb framebuffer plugin does not support 8bit color depth?

SGaist

Hi and welcome to devnet,

AFAIK, there should be no such limitation.

Which version of Qt are you using ?
Did you cross-compile it yourself ?
Do you have the same issue with a simple dummy application ?

Meyton_GmbH 0

Thank you for your reply!

I'm using Qt 5.12.8 which is cross-complied via buildroot. I tested it again with this super simple program.

#include  <QApplication>
#include  <QLabel>

int main( int argc, char *argv[] )
{
  QApplication *app = new QApplication( argc, argv );
  QLabel *label = new QLabel( "This is a test!" );
  label->show();

  return app->exec();
}

But the result is still the same. It does not work with 8bit famebuffer. I tested it on another machine which supports 8bit and 16bit color depth. If I switch the framebuffer to 16bit color it runs fine. If I switch the framebuffer to 8bit color depth, I get the same errors as before.

/tmp/test -platform linuxfb

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::setPen: Painter not active
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setCompositionMode: Painter not active
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setCompositionMode: Painter not active
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::setPen: Painter not active
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::setPen: Painter not active
QPainter::setCompositionMode: Painter not active
QPainter::setCompositionMode: Painter not active

SGaist

Looking at the code it seems that 8 bit does not have a QImage format associated to it hence the error you see.

You may have to modify the QPA plugin.

Meyton_GmbH 0

So Qt5 does not support 8bit color depth out of the box like Qtopia 4 anymore?

SGaist

The code looks pretty similar between both code bases.

What was your configuration for Qtopia ? Where you using DirectFB ?

Meyton_GmbH 0

Before porting to Qt5 I was using Qtopia 4.7.5 with QWS.

SGaist

That does not give the information I requested.

Meyton_GmbH 0

This was the QTopia 4.7.5 build configuration:

#!/bin/bash

./configure \
-embedded x86 \
-prefix /opt/qtopia-4.7.5_webkit \
-commercial \
-shared \
-no-largefile \
-exceptions \
-xmlpatterns \
-no-multimedia \
-no-audio-backend \
-no-phonon \
-no-phonon-backend \
-svg \
-webkit \
-javascript-jit \
-no-script \
-no-scripttools \
-no-declarative \
-no-mmx \
-no-3dnow \
-no-sse \
-no-sse2 \
-no-sse3 \
-no-ssse3 \
-no-sse4.1 \
-no-sse4.2 \
-no-avx \
-no-neon \
-qt-zlib \
-qt-gif \
-qt-libtiff \
-qt-libpng \
-qt-libmng \
-qt-libjpeg \
-qt-freetype \
-depths all \
-qt-decoration-windows \
-plugin-decoration-windows \
-no-opengl \
-qt-gfx-linuxfb \
-qt-gfx-qvfb \
-qt-kbd-tty \
-qt-kbd-qvfb \
-qt-mouse-pc \
-qt-mouse-qvfb \
-no-glib

Framebuffer was QWS LinuxFB.

SGaist

Do you need windowing support ?

Meyton_GmbH 0

@SGaist said in Qt5 linuxfb platform plugin does not work with 8bit color depth:

Do you need windowing support ?

Would be nice, but I could work around this if I can get the application running with 8bit color depth.

SGaist

Then you should check wayland and see if it runs on your target at the depth you are looking for.

By the way, I see the commercial option. If you are a commercial user, you should contact the Qt Company support.