Qt: resizable and movable main window without title bar

Question

I need draw a Qt-window without the title bar. Generally this can be easy by just setting the CustomizeWindowHint window attribute. But then window has fixed size and position.

I need a movable and resizable window. This post shows how to move the window manually so I wonder whether there is a way to at least keep the borders resizable.

Of course I can also resize the window manually but I expect jumping windows and many sorts of weird behavior so I hope there is a way to use the existing functionality

Answer 1

Edit: I got it

---

There is some jumping behavior but this is a working manual resize/move of window without a title bar I implemented for my personal project:

//Below two methods partially from Qt Shaped Clock example
void MainWindow::mousePressEvent(QMouseEvent *event){
//From Qt Documentation:
//Reason why pos() wasn't working is because the global
//position at time of event may be very different
//This is why the mpos = event->pos(); line before was
//possibly causing jumping behavior

     if (event->button() == Qt::LeftButton){
         //Coordinates have been mapped such that the mouse position is relative to the
         //upper left of the main window
         mpos = event->globalPos() - frameGeometry().topLeft();

         //At the moment of mouse click, capture global position and
         //lock the size of window for resizing
         global_mpos = event->globalPos();
         storeWidth = this->width();
         storeHeight= this->height();

         event->accept();

     }   

}

void MainWindow::mouseMoveEvent(QMouseEvent *event){

    //mapped mouse relative to upper left of window
    rs_mpos=event->globalPos()-frameGeometry().topLeft();//general position tracker for resizing
    QTextStream out(stdout);

    //How much of the corner is considered a "resizing zone"
    //I was experiencing jumping behavior with rs_size is 10 so
    //I recommend rs_size=50
    int rs_size=50;

    //Big if statement checks if your mouse is in the upper left,
    //upper right, lower left, and lower right 
    if ( (abs(rs_mpos.x()) < rs_size && abs(rs_mpos.y()) < rs_size) ||
     (abs(rs_mpos.x()) > this->width()-rs_size && abs(rs_mpos.y()) <rs_size) ||
     (abs(rs_mpos.x()) < rs_size && abs(rs_mpos.y())> this->height()-rs_size) ||
     (abs(rs_mpos.x()) > this->width()-rs_size && abs(rs_mpos.y())> this->height()-rs_size)

     ){



         //Below for debugging
         /*
         out << rs_mpos.x() << " , " << rs_mpos.y() << "\n";
         out << "window: " << this->width() << " , " << this->height() << "\n";
         out << "globalpos: " << event->globalPos().x() << " , " 
             << event->globalPos().y() << "\n";
         */

        //Use 2x2 matrix to adjust how much you are resizing and how much you
        //are moving. Since the default coordinates are relative to upper left
        //You cannot just have one way of resizing and moving the window.
        //It will depend on which corner you are referring to

        //adjXfac and adjYfac are for calculating the difference between your
        //current mouse position and where your mouse was when you clicked.
        //With respect to the upper left corner, moving your mouse to the right
        //is an increase in coordinates, moving mouse to the bottom is increase
        //etc.
        //However, with other corners this is not so and since I chose to subtract
        //This difference at the end for resizing, adjXfac and adjYfac should be
        //1 or -1 depending on whether moving the mouse in the x or y directions
        //increases or decreases the coordinates respectively. 

        //transXfac transYfac is to move the window over. Resizing the window does not
        //automatically pull the window back toward your mouse. This is what
        //transfac is for (translate window in some direction). It will be either
        //0 or 1 depending on whether you need to translate in that direction.

        //Initiate matrix
        int adjXfac=0;
        int adjYfac=0;
        int transXfac=0;
        int transYfac=0;

        //Upper left corner section
        if ( (abs(rs_mpos.x()) < rs_size && abs(rs_mpos.y()) < rs_size)){
        this->setCursor(Qt::SizeFDiagCursor);



             //Upper left. No flipping of axis, no translating window
             adjXfac=1;
             adjYfac=1;

             transXfac=0;
             transYfac=0;



        }
        //Upper right corner section
        else if(abs(rs_mpos.x()) > this->width()-rs_size &&
                abs(rs_mpos.y()) <rs_size){
            this->setCursor(Qt::SizeBDiagCursor);


            //upper right. Flip displacements in mouse movement across x axis
            //and translate window left toward the mouse
            adjXfac=-1;
            adjYfac=1;

            transXfac = 1;
            transYfac =0;

         }

         //Lower left corner section
         else if(abs(rs_mpos.x()) < rs_size &&
                 abs(rs_mpos.y())> this->height()-rs_size){
            this->setCursor(Qt::SizeBDiagCursor);

            //lower left. Flip displacements in mouse movement across y axis
            //and translate window up toward mouse
            adjXfac=1;
            adjYfac=-1;

            transXfac=0;
            transYfac=1;


          }
          //Lower right corner section
          else if(abs(rs_mpos.x()) > this->width()-rs_size &&
                  abs(rs_mpos.y())> this->height()-rs_size){
              this->setCursor(Qt::SizeFDiagCursor);

             //lower right. Flip mouse displacements on both axis and
             //translate in both x and y direction left and up toward mouse.
             adjXfac=-1;
             adjYfac=-1;

             transXfac=1;
             transYfac=1;
            }

       if (event->buttons()==Qt::LeftButton ){

           //Calculation of displacement. adjXfac=1 means normal displacement
           //adjXfac=-1 means flip over axis     
           int adjXdiff = adjXfac*(event->globalPos().x() - global_mpos.x());

           int adjYdiff = adjYfac*(event->globalPos().y() - global_mpos.y());

           //if transfac is 1 then movepoint of mouse is translated     
           QPoint movePoint(mpos.x() - transXfac*adjXdiff, mpos.y()-transYfac*adjYdiff);
           move(event->globalPos()-movePoint);
           resize(storeWidth-adjXdiff, storeHeight-adjYdiff);

           event->accept();


         }

    }

     //in any move event if it is not in a resize region use the default cursor
     else{

         this->setCursor(Qt::ArrowCursor);


          //simple move section
          if (event->buttons()==Qt::LeftButton &&
              resizeZone==false){
              move(event->globalPos() - mpos);
              event->accept();
          }


     }

}

Set these in your header file

private:
    QPoint mpos; //For dragging, relative mouse position to upper left
    QPoint global_mpos; //For resizing, global mouse position at mouse click
    QPoint rs_mpos; //for resizing
    int storeWidth; //fix window size at mouseclick for resizing
    int storeHeight;

Answer 2

From the docs on Qt::CustomizeWindowHint:

This flag must be set to allow the WindowTitleHint, WindowSystemMenuHint, WindowMinimizeButtonHint, WindowMaximizeButtonHint and WindowCloseButtonHint flags to be changed.

Basically, Qt::CustomizeWindowHint is not meant to be used without other title bar hints.

Use Qt::FramelessWindowHint in conjunction with some event reimplentation for dragging (see the solution to your other question). You can get a size grip to show like so:

auto statusBarWidget = statusBar();
statusBarWidget->setSizeGripEnabled(true);

You may need to do some work with the size grip and status bar to work with the frameless window flag set.

Edit: since you aren't using a statusbar, add a "hotspot" in your central widget to start resizing instead of moving, i.e. check if the mouse is in the bottom right corner of the window and set the cursor appropriately. If they click, begin resizing instead of moving. This can all be done by reimplementing the mouse events.