[Interest] Rendering timing of qt

[Lodron, Gerald]

Hi


I am using a display as a projector for a camera/projector setup. Here i want to display an Image using qt, trigger my cameras (so cameras do NOT coninously grab) and view the reflection of the display on a mirror like surface.


I am using a QLabel with a setPixmap call from an qimage. in sum i have 12 different qimages in memory. To control my display i programmed a seperate thread which polls over an external signal (IP port). when i get those signal (in different thread as the GUI main thread) the thread calls the setPixmap function and then returns. After that my cameras get triggered (from the program wich sends the extern signal) and the images from the cameras are stored/processed somehow.


The problem is that my cameras sometimes record the old pixmap, so for me it seems that the setPixmap do not immideately performs a repaint action of the qwidget. I think that the repaint event must be triggered from the main gui thread at some time because when i put a sleep of several hundret milliseconds after setPixmap and before trigger cameras it works. I also tested using a update call, without effect. And it seems that i am not allowed to call repaint from my seperate thread because then the qlabel looks really strange.... I dont like to sleep so long because my cameras can make 30 frames per second which i want to use, so i twould be great if i could force a qlabel update with 30Hz somehow....


So my question:

-> is it possible to perform a fast repaint action? Do i need to swich my command polling thread to main thread for this?

-> can i get a kind of response/signal when the repaint is finished so that i can immedialtely trigger the cameras?

-> can someone explain me the timing and order/process of repaint(ing)


Or shouldn't i use qt for this, which also would be an answer....


thanks,

Gerald Lodron