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InactivityTimer — Sleep/Wake Event Filter Implementation

Application level sleep/wake implementation through event filter in Qt EGLFS.

This timer is used for dimming or blanking the screen on Qt EGLFS application when there is no keyboard or mouse activity for a period of time. Once keyboard or mouse is pressed. the screen will then wake up to the full brightness.

This timer make use of QEvent::KeyPress and QEvent::MouseMove hooks and waits for the hooks to trigger and adjust the screen brightness by writing a value (0 to 255) to /sys/class/backlight/rpi_backlight/brightness. It is used to replace system level screen saver/screen blanking on Raspbian, which doesn't work if the Qt application run directly on top of EGLFS.

The 4 variables in this timer are:

filter.setDebug(false);
filter.setTimeOut(60000); // microseconds before inactivity kicks in, defaults to 1 minute
filter.setMinBrightness(12); // 7" official touchscreen brightness (0 to 255), higher is brighter
filter.setMaxBrightness(200);

To use this sleep/wake event filter in your Qt application, drop in customeventfilter.h and customeventfilter.cpp to your project, include the header in your main.cpp and install the filter to the instance of QApplication:

#include "mainwindow.h"
#include <QApplication>
#include <customeventfilter.h>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    CustomEventFilter filter;
    filter.setDebug(false);
    filter.setTimeOut(60000);
    filter.setMinBrightness(12);
    filter.setMaxBrightness(200);
    a.installEventFilter(&filter);

    return a.exec();
}

Tested on

  • Raspbian Jessie Lite
  • Raspberry Pi 2 Model B
  • Official 7" Touchscreen