[Development] [QML][EGLFS] Bits depth

[Denis Shienkov]

Hi guys,

I have use Qt 5.7 on Linux Embedded board (Toradex Apalis T30) with the
EGLFS via X11 platform (NVidia drivers).

My QML application uses 24-bit PNG images. But I see that these images is
looks like 16-bit (I see the gradients borders, and it looks ugly),
howewer my X11 uses DefaultDepth == 24!!!

Also this command:

{quote}
root at apalis-t30:~/deploy-apps# xdpyinfo | grep 'depth of root'
  depth of root window:    24 planes
{quote}

shows 24-bit mode too.

Next, I have added this debug env variable:

{quote}
 export QSG_INFO=1
{quote}

to see what happens when my QML app starts:

{quote}
...
qt.scenegraph.general: threaded render loop
qt.scenegraph.general: Using sg animation driver
qt.scenegraph.general: Animation Driver: using vsync: 16.67 ms
qt.scenegraph.general: Animation Driver: using vsync: 16.67 ms
qt.scenegraph.general: texture atlas dimensions: 2048x2048
qt.scenegraph.general: R/G/B/A Buffers:    5 6 5 0
qt.scenegraph.general: Depth Buffer:       16
qt.scenegraph.general: Stencil Buffer:     8
qt.scenegraph.general: Samples:            0
qt.scenegraph.general: GL_VENDOR:          NVIDIA Corporation
qt.scenegraph.general: GL_RENDERER:        NVIDIA Tegra 3
...
{quote}

I see that OpenGL (yes?) initializes with the "R/G/B/A Buffers:    5 6 5 0"
mode,
that is 16-bit depth!!! O_O

Next, I have tried to change the FB depth via:

{quote}
  fbset -fb /dev/fb1 -depth 24
{quote}

I see that FB changes own settings, but nothing changes when my app starts,
it still shows images ugly, as 16-bit depth.

Also I have tried to use QT_QPA_EGLFS_DEPTH variable (with 16, 24 or 32),
but nothing changes, not helps.

Helps only the QT_QPA_EGLFS_FORCE888 variable, but it introduces others bad
issues,
like the whole/half HDMI display flickering.. So, I can not to use
QT_QPA_EGLFS_FORCE888..

So, is there are any tricks to use 24-bit depth?

BR,
Denis
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