I'm running the Qt5 application on my raspberry pi and I would like to introduce some kind of a power-saving feature.
I don't use x11 or wayland, because I don't need it, but I use gles2 (OpenGL for Embedded Systems).
I want to use
tvservice --off and
tvservice --preferred to toggle between turned off / turned on screen.
My problem is that when I call
tvservice --preferred the display turns on but the screen is black (no application output is shown).
How can I turn it on and see the application that was running previously?
When I restart the Qt5 application - it's being displayed correctly.
Changing foreground virtual terminal with
chvt (as suggested here) does not help.
Changing framebuffer depth to different and back again with
fbset -depth 16 ; fbset -depth 32 (I've seen it on some forum, cannot find which) also does not help.