QDesktopWidget::screenGeometry returning incorrect value

Question

I have Qt 5.3 running on top of DirectFB 1.7.4 (along with a tiny patch to qdirectfbintegration because platformNativeInterface was not implemented).

I come up in 3840x2160 resolution, then change to 1920x1080 resolution using the code below. The resolution changes and I can confirm looking at fbset output. The problem I am seeing is that after changing the resolution to 1920x1080 Qt still reports it as 3840x2160.

Does anyone know how to force Qt to recheck/update the resolution it is reporting? Or what might be missing from the directfb plugin to notify Qt that something has changed under the hood?

Thanks.

IDirectFB * dfb = (IDirectFB*)m_app->platformNativeInterface();
if(dfb){
    std::cerr << "######## New resolution is " << width << "x" << height << std::endl;

    IDirectFBDisplayLayer *layer;
    DFBDisplayLayerConfig config;

    std::cerr << "######## Getting primary IDirectFBDisplayLayer" << std::endl;
    /* Get an interface to the primary layer. */
    dfb->GetDisplayLayer(dfb, DLID_PRIMARY, &layer);
    if(layer){
        DFBResult dres;
        std::cerr << "######## Got the primary display layer, setting admin" << std::endl;
        // This level allows window stack mode switches
        dres = layer->SetCooperativeLevel(layer, DLSCL_ADMINISTRATIVE);
        if(dres != DFB_OK){
            std::cerr << "######## Error: " << DirectFBErrorString(dres) << std::endl;
        }

        std::cerr << "######## Getting layer configuration" << std::endl;
        // Get layer configuration
        dres = layer->GetConfiguration(layer, &config);
        if(dres != DFB_OK){
            std::cerr << "######## Error: " << DirectFBErrorString(dres) << std::endl;
        }
        // Set the new resolution
        std::cerr << "######## Setting layer resolution" << std::endl;
        config.width = width;
        config.height = height;
        dres = layer->SetConfiguration(layer, &config);
        if(dres != DFB_OK){
            std::cerr << "######## Error: " << DirectFBErrorString(dres) << std::endl;
        }
    }

    // Print out resolution from Qt
    QRect res = QApplication::desktop()->screenGeometry();
    std::cerr << "######## QApplication resolution is now " << res.width() << "x" << res.height() << std::endl;

The output I see from the console is: ######## New resolution is 1920x1080 ######## Getting primary IDirectFBDisplayLayer ######## Got the primary display layer, setting admin ######## Getting layer configuration ######## Setting layer resolution (*) FBDev/Mode: Setting 1920x1080 ARGB (*) FBDev/Mode: Switched to 1920x1080 (virtual 1920x2160) at 32 bit (ARGB), pitch 7680 ######## QApplication resolution is now 3840x2160 root@output:~# fbset mode "1920x1080-24" # D: 74.250 MHz, H: 27.000 kHz, V: 24.000 Hz geometry 1920 1080 1920 2160 32 timings 13468 148 638 36 4 44 5 accel false rgba 8/16,8/8,8/0,8/24 endmode

Answer 1

The directfb qpa plugin is lacking several features. I'm working on some updates to the plugin, I'll post a link here when I submit them.

For a temporary workaround calling:

WindowSystemInterface::handleScreenGeometryChange(m_app->screens().first(), QRect(0,0,width,height));

is working to update the resolution in Qt.