OpenEuphoria

2. Re: Windows vertical retrace

• Posted by Derek Parnell <ddparnell at bigpond.com> Jun 21, 2006
• 570 views

ags wrote:
> 
> Hi All
> 
> After a quick google it seems to me that there is no way to detect the
> vertical
> retrace on the windows desktop (ie 'non-exclusive' mode).

You don't have to with Windows GUI programming. The 'trick' is to do your
drawing onto a Pixmap control and then copy the Pixmap to the Window during the
w32HPaint event. The way to trigger that event is to call

  repaintFG(mywindow)

If you want to see how this is down you can explore the 'wordcatcher' demo
program that comes with win32lib.

-- 
Derek Parnell
Melbourne, Australia
Skype name: derek.j.parnell

4. Re: Windows vertical retrace

• Posted by Derek Parnell <ddparnell at bigpond.com> Jun 21, 2006
• 569 views

ags wrote:

> One question though.. why is there no non-erasing equivalent for paintRect?

Because nobody asked for it.

global procedure redrawRect( integer id, integer x1, integer y1, integer x2,
integer y2 )

    -- Redraws only a portion of the window
    atom hWnd
    atom rect

    -- Allocate rectangle
    rect = w32acquire_mem( 0, SIZEOF_RECT )
    poke4(rect, {x1,y1,x2,y2})

    hWnd = getHandle( id )

    -- invalidate sub-window of the current window
    if w32Func( xInvalidateRect, {hWnd, rect, 0} ) then
        VOID = w32Func(xSendMessage,{hWnd, WM_PAINT, 0, 0 })
    end if

    -- Free the rectangle structure
    w32release_mem( rect )

end procedure

-- 
Derek Parnell
Melbourne, Australia
Skype name: derek.j.parnell

6. Re: Windows vertical retrace

• Posted by Cuvier Christian <christian.cuvier at insee.fr> Jun 22, 2006
• 583 views

> Subject: Windows vertical retrace
> 
> 
> posted by: ags <eu at 531pi.co.nz>
> 
> Hi All
> 
> After a quick google it seems to me that there is no way to 
> detect the vertical retrace on the windows desktop (ie 
> 'non-exclusive' mode).
> 
> With rapidly updating graphics in a small window on my home 
> system with a CRT monitor the flicker is quite noticeable.  
> On my work system with an LCD monitor the effect is not as 
> bad but still there (particularly if the mouse pointer is 
> over the area being drawn).
> 
> So what do other systems do about this?  Flash objects in web 
> pages don't seem to suffer from this and other windowed games 
> seem to get around the problem.  How are they doing this?  
> How can we do this in Euphoria, particularly with win32lib?
> 
> Gary
> 
> 

I once read that screen flickering  was caused by painting the same area
several times in a rapid succession, and that efficient flicker reduction
could be made through eliminating the extra drawing.

For instance, when you repaint a window, the window gets a WM_ERASEBKGND
message to erase the background, then the WM_PAINT. If you paint by copying
a whole dc or pixmap, the drawing done while processing the first message is
redundant, causes screen flicker and slows the app down. Trap the
WM_ERASEBKGND message and process it by just returning -1 (or w32True). Docs
say anything nonzero does the job.

This particular aspect is not the only source of flicker, but an often
overlooked one. Ihave seen it in action. Again, the trick is avoiding to
paint a region and then immediately redraw something else in it.

HTH
CChris