i put together a small code snippet for QtCreator, to better showcase the issue i see in my dual-head setup with a Qt widget app running through EGLFS on a libMali.so/DRM/KMS setup on Allwinner A20 mainline based OS:
the outcome is the wrong display of the two (yellow and red) rectangles with the code above only on the ext HDMI diplay. see:
the puzzling issue is that if i comment out the w2.show() line:
i can see (correctly) a single yellow screen on the primary LCD display.
can someone point me toward better debugging? is a GDB step by step approach the best one? the Qt stack is that huge..