QT realizes multi screen and multi-resolution adaptation

Here is only a brief description of the implementation idea .

Operating conditions

• Two screens , Different resolution .
• Qt Software

Ask questions

I wrote a software some time ago , There is self drawn content in the window .
The length units used in the self drawn content are all pixels . As one can imagine , On the developer's computer screen, the size meets the requirements . No problem at this point .
After the software development is completed, it will be sent to the customer , The customer runs on his computer , Also no problem , After all, the resolution is about the same .
Run the software on a computer equipped with a high-resolution display once in a while , stay 4k Under screen , The software has the following problems ：

• Overall dimensions and some self drawn content （ Line shape ） Become small , The reason is that the screen resolution has increased , More dense pixels , The same number of pixels looks shorter , This is easier to understand .
• In addition to some self drawn content , Like words , But it doesn't get smaller . This is because when drawing text , Font size is set using setPointSize, Make the text drawn on any display the same size .
• The final result is , The text looks big , The graph becomes very small .

resolvent

Realize multi screen resolution adaptation

There are two situations to discuss here .

1. Use only one screen
   In this case , Just do the following ：

• When drawing a graph , Draw in millimeters .
• Get screen resolution , Add length -> Pixel conversion function , Convert each length into pixel length and pass it to the drawing function .
  In this way, the self drawing content adaptation under different resolutions can be realized .

2. Use multiple screens with different resolutions
   In this case , It involves the problem of window dragging .
   When a software window is dragged from one window to another , It needs to be retouched .
   The following work needs to be done ：

• Design window resolution change notification signal
  stay Qt No relevant notification mechanism was found in , We can do it in paint Function to detect whether the current screen of the window has changed , If there is a change , Send a signal . Here is an implementation code , Used to determine whether the main screen changes ：

bool Global::checkIfScreenChanged()
{
    
    static int screen_number = -1;

    bool changed = false;
    QWidget *w = mainWindow();
    QDesktopWidget *dk = QApplication::desktop();
    int new_screen_number = dk->screenNumber(w);
    if (screen_number != new_screen_number)
    {
    
        screen_number = new_screen_number;
        changed = true;

        //  A notice 
        emit sigScreenChanged(screen_number);
    }

    return changed;
}

• Rearrange and draw
  After receiving the window screen change message , Re layout 、 draw .

Realization effect

The expected effect has been achieved .

Conclusion

Windows Software on , such as office、WPS All of them deal with multi-resolution and multi screen , You can open any of the above software and drag it from one window to another , Across the screen , The software will be rearranged . And we use this method to achieve the same effect .

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