[PATCH] Flicker less drawing

[Chris January]

Thanks.
 
I checked in some of your patch. I'm still checking removing the erase. I
don't think this is the right way to solve this - I think
QETWidget::translatePaintEvent is a better candidate. Also you'll notice
repaint is already called by translateConfigEvent further done. It would
appear the logic in the if statement needs correcting rather than adding an
extra repaint in further up.
 
Cheers,
Chris

Hi,
In file qwidget_win.cpp, in function
    void QWidget::repaint( int x, int y, int w, int h, bool erase )
lines 1547-1548
    QPaintEvent e( r, erase );
    if ( r != rect() )
        qt_set_paintevent_clipping( this, r );
 -> if ( erase )
 ->     this->erase( x, y, w, h );
    QApplication::sendEvent( this, &e );

If erasing is needed, it is done with erase(). I dont know where but it
seems to be done a second time in response to the QPaintEvent raised. So I
removed this 2 lines:
    if ( erase )
        this->erase( x, y, w, h );
and it removed the flickering I saw on the application I am testing. 
 
In file qapplication_win.cpp, lines 5653 & 5705, QWidget window class style
is:
 
wcx.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
 
I always hated CS_HREDRAW and CS_VREDRAW styles. They cause entire window
redrawing => background erasing + redrawing, which causes flickering. I
removed this 2 styles. But, if the window size grows, then painting is
needed.
So I modified
    QETWidget::translateConfigEvent
line 4831:
  if ( isVisible() ) {
        QResizeEvent e( newSize, oldSize );
        QApplication::sendSpontaneousEvent( this, &e );
  
  ->     this->repaint();
    } else {
        QResizeEvent * e = new QResizeEvent( newSize, oldSize );
        QApplication::postEvent( this, e );
    }                        

I added the repaint() call.
 
After that, there is less flickering. This is also true with the dirview
example. But more testing is needed.
There is something strange : if you resize the window backwards  / forwards
horizontally OR vertically, it doesn't flicker. It you resize both
horizontally and vertically (bottom right corner), it does. I think it is
because the 2 resize events are not merged, but 2 events = 2 repaint() are
received / called very shortly. I tried to batch the repaint() call with
InvalidateRect / postEvent(), but it does nothing. But it is the same
behaviour with Qt 2.3 NC. So, if the patch is approved, maybe the bug "[
1060157 ] Unnecessary flicker during repaint" could be considered corrected.
 
Here are the diff output from my local CVS copy:
-----------------------------------8<---------------------------------------
-------
diff -r1.1.2.30.2.23 qapplication_win.cpp
4831a4832,4833
> 
>                 this->repaint();
4835c4837
<             }
---
>             }                        
5653c5655
<     wcx.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
---
>     wcx.style = CS_DBLCLKS; // | CS_HREDRAW | CS_VREDRAW;
5705c5707
<     wcx.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
---
>     wcx.style = CS_DBLCLKS; // | CS_HREDRAW | CS_VREDRAW;
-----------------------------------8<---------------------------------------
-------
diff -r1.1.2.15.2.14 qwidget_win.cpp
1547,1548c1547,1548
<         if ( erase )
<             this->erase( x, y, w, h );
---
>         //if ( erase )
>         //    this->erase( x, y, w, h );
-----------------------------------8<---------------------------------------
-------
 
Regards.


Aurelien REGAT-BARREL 




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