[Bf-committers] Back Buffer Issues

Matthew H. Plough mplough at Princeton.EDU
Thu Dec 2 23:50:06 CET 2004


Since this email pertains to the bf-committers discussion and also 
pertains to documentation, I am sending it to both bf-committers and 
bf-webcontent.

After reading Daniel Dunbar's notes on the problems with front- and 
back-buffer display schemes at 
http://www.zuster.org/blender/drawingArchitecture.html , I understand 
why no fix is possible.  However, no information is readily available on 
the topic on any of the Blender web sites.  My card, and many other 
cards on the market, do page flipping by default for performance 
reasons.  Many of them can be switched to swap copy mode in the advanced 
preferences.  Could we put this up on 
http://www.blender3d.org/cms/Graphics_Cards.201.0.html , the page with 
graphics card troubleshooting information? 

I suggest adding the following, or something similar:

Common Issues
o Some consumer...Display Properties.
[add] o Blender's menus may be displayed incorrectly in certain buffer 
swap modes.  Try changing the swap mode to Swap Copy in the 
vendor-specific area of the <a href="#1118" target="_top">Advanced 
Display Properties</a>.

I would not mind becoming the maintainer of that page. 

Matt

Ton Roosendaal wrote:

> Hi,
>
> Blender likes the SwapCopy a lot. :)
> This is becoming a standard in many (PC) cards now, and for some  
> systems you cannot even tweak it... for example Macs only support 
> this  method.
>
> The Swap-Exchange could work too, it is the old Blender default from  
> the SGI period, but for it to work 100% I need someone with such a  
> graphics card system who's devoted to get it to work. Not difficult  
> coding, just tracking all little things in the code to keep it  
> swap-exchange compatible.
>
> A year ago we discussed this here too, with Daniel Dunbar, going over  
> the best buffer strategy with Blender. The conclusion back then was 
> to  go for 100% swap-copy, and code exceptions for the (older) systems 
> that  don't support this.
>
> Now, what's there to fix?
>
> -Ton-
>
>
>
> On 2 Dec, 2004, at 19:25, Matthew H. Plough wrote:
>
>> Hi all!!
>>
>> I was playing around with my video card's OpenGL settings this  
>> morning, and found an interesting clue on what's causing the odd  
>> corruption shown in  
>> http://www.princeton.edu/~mplough/tmp/buttons_error.png .
>> First things first: I have a 3Dlabs Wildcat Realizm 200.
>>
>> Second things second ;) : Like most cards, my card has two options 
>> for  dealing with double buffering -- page flipping (which only 
>> exchanges  the front and back buffer pointers) and Force Swap Copy 
>> (which  maintains a dedicated back buffer and a dedicated display 
>> buffer).   When a buffer swap happens in forced mode, data from the 
>> back buffer  is *copied* into the display buffer, but is not 
>> cleared.  My best  interpretation of Blender's code leads me to 
>> believe that it depends  on this preservation of back buffer data.
>> Is this in fact the case?  If so, how can we fix this?
>>
>> Matt
>


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