[directfb-dev] Re: Help me please! About 4bits pixel format.

[James Su <suzhe@gnuchina.org>]

Then, must I remeber whether the sub surface begins at odd pixel? Or is 
there some way to get this information from current data structure?

Regards
James Su

Henric Andersson wrote:

>Sorry about the previous mail, wrong button combo :)
>
>  
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>>Hi,
>>So sorry to bother you, but I really want to implement 4bits pixel
>>format for DirectFB. The source code of DirectFB almost drives me crazy.
>>Could you please give me some more hint or information?
>>Until now, I did not understand the structure of DirectFB clearly,
>>especially the surface memory management. In my understanding, a surface
>>may occupy a block of memory itself or share a block of memory with
>>other surface, ie. a sub surface. Am I right? Then, for example if I
>>alloc a sub surface from an odd x coordination within the father
>>surface, i.e. (3,4), the memory offset of the sub surface will be 1.5
>>bytes, but it's impossible! There are many other similar problems in
>>DirectFB to prevent me implementing 4bpp format. But it is very
>>    
>>
>
>It is possible to use uneven X coordinates. You have to work at a bit level
>though. So, if you would highlight the first pixel of a row, you would only
>manipulate the first 4 bits. The next pixel would use the higher 4 bits of
>the same byte, the next (3rd) pixel would use the lower 4 bits of the second
>byte, and so on.
>
>Hope it helps...
>
>/Henric
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