OpenEuphoria

Re: double buffering

• Posted by euman at bellsouth.net Aug 16, 2001
• 489 views

Here is an example from a current project I am working on....
Hope it explains things some

       -- Double buffer
       -- first create the initial DC and fill it with a compatible bitmap
(magic bitmap)
       -- The CreateCompatibleDC function creates a memory device context (DC)
compatible with the specified device.
       memdc = c_func(xCreateCompatibleDC, {hdc}) -- make sure we destroy this
when we exit the prog
       hbit  = c_func(xCreateCompatibleBitmap, {hdc, 640, 480})

       -- select the brush for the background into the memdc along with the
"magic bitmap" ;)
       -- The SelectObject function selects an object into the specified device
context (DC).
       -- The new object replaces the previous object of the same type.
       -- in this case the objects are not the same (one is a brush and the
other is a bitmap)
       junk  = c_func(xSelectObject,{memdc, hbrush})
       junk  = c_func(xSelectObject,{memdc, hbit})

       -- The PatBlt function paints the specified rectangle using the brush
that is currently selected
       -- into the specified device context. The brush color and the surface
color or colors are combined
       -- by using the specified raster operation.
       junk = c_func(xPatBlt, {memdc, 0, 0, 640, 480, PATCOPY})

       bitdc = c_func(xCreateCompatibleDC, {hdc}) -- make sure we destroy this
when we exit the prog

       -- run our function (defined above) to return an address to our Device
Independant Bitmaps
       hDib = createDIB(butbar2[1], butbar2[2], hdc )
       junk  = c_func(xSelectObject,{bitdc, hDib})

       junk  = c_func(xBitBlt,{memdc, 517, 0, 114, 480,bitdc,0,0,SRCCOPY})

Count the DC's and note that BitBlt is used to fill the memdc with an image
which
in this case happens to be an image in bitdc.
If I use bitdc as a temporary holder for a DIB I can place multiple images in
memdc.
The reason for this is when you need a Paint refresh, copying memdc to your hdc
in
one swoop is very-very fast.

elsif iMsg = WM_PAINT then
        hdc = c_func(BeginPaint, {hwnd,ps})
        junk  = c_func(xBitBlt,{hdc, 0, 0,640,480,memdc,0,0,SRCCOPY})
        c_proc(EndPaint, {hwnd, ps})

In my program I am copying 10 bitmap images to the screen all at once
(code for all of this not in this message but this is a general overview)
and there is no flicker or stacking look when the images are painted...

Euman
euman at bellsouth.net


----- Original Message -----
From: <dstanger at belco.bc.ca>
To: "EUforum" <EUforum at topica.com>
Sent: Tuesday, August 14, 2001 17:31
Subject: double buffering


>
> Hi all,
>
> When Derek was talking about graphic animation he mentioned the term "double
> buffering". What is that?
>
> Thanks,
> David S.
>
>
>
>
>