Touchscreen bounces with Qt app.

  • Today I got a new panel PC, I believe it may be the cheapest one available. The thing has an Ltd eGalax touchscreen and with Ubuntu 16.04 LTS installed it works out of the box like a charm.

    But when I run my Qt application, the touchscreen bounces.....alot. When I boot to the desktop there seems to be no problem at all. The virtual keyboard of ubuntu also works perfect. My fancy Qtumbler does not work now :(

    My application is run on it's own desktop (so it can run fullscreen).

    I do not know where the problem might be. The problem might be related to Qt (5.8) or it might related to the separate desktop. But I have no way to test this.

    I don't know if there are any known issues between Qt apps and certain touchscreen drivers??

  • Moderators

    @bask185 said in Touchscreen bounces with Qt app.:

    But when I run my Qt application, the touchscreen bounces.....alot.

    what exactly does this mean?

  • I mean it bounces just like a bouncing switch. When I hold my finger on a pushbutton (yes, autorepeat is disabled), I see the state toggling and events are being executed continously instead of just one time. This prevents me from using the Qtumbler :(

  • So nobody has a clue why Qt on this systems behaves like this?

  • Lifetime Qt Champion


    Do you have the same strange behaviour if you compile your application your distribution provided Qt ?

  • @SGaist No I only have it on this particular panel PC. The PC has ubuntu installed like my host pc and other panel PCs

    Unfortunately this thing must be shipped out as a pilot. So I have to fix the flickering. I tried using QThread::msleep(); but that does not solve the problem it only makes it slower.

    If I push a button and the msleep is set at 300ms I am still getting 3 events instead of just 1.

    I think I came up with a viable simple solution. When I push a button I want to set a boolean variable true and let it go to false after a time has expired. When the boolean is set to true, no actions will happen.


    void on_pushbutton_clicked()
       if(boolean == false) {

  • Lifetime Qt Champion

    Usually de-bouncing is done using a single shot timer that is connected to the actual slot that will do something.

Log in to reply

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.