[GEM Development] Video mode - bitplane vs packed pixels

[Michael Bernstein]

Hi Cyprian,

>>     So the proper handling of offscreen bitmap is:
>> 
>>     - Make your graphic handling with a buffer in the standard format. The
>>     field fd_stand of the MFDB structure for this buffer is 1.
>>     - Then call vr_trnfm() to transform the standard format graphic buffer
>>     to a device-dependant buffer (fd_stand = 0 for destination MFDB). This
>>     transformation may be done in place. But this took a longer time. So
>>     better use a second buffer for the destination.
>>     - Then use vro_cpyfm() to copy the graphic buffer in hardware dependant
>>     format to the screen buffer. The field fd_addr of the destination MFDB
>>     is set to NULL (0) and all other field can stay uninitialized.
> 
> 
> good point,
> Initially I had a plan to do that conversion on myself due to 
> performance and memory limitations, but I'll try to do that in a proper 
> way: image --> vr_trnfm --> vro_cpyf.
> It might work in low color video modes, but it may run out of RAM in 256 
> color modes. I need 1x buffer for loaded image, 1x buffer for standard 
> image, 1x optional buffer in device-dependent buffer.

Yes, do the conversion by yourself can be faster. And while i wrote my 
answer i also had the possible problem of not enough memory in mind.

> Actually I'm quite familiar with Atari stuff. I have paper Profibuch 
> book, I'm on daily basis on TosHyp and Atari-forum.com.

Some yeas ago i was also working on tos.hyp. After the first author lost 
his interest in Atari, i recompiled the hypertext. After his homepage 
was back, i wrote him, that i recompiled tos.hyp and dont wont let it 
die. So he decided to put it under GPL. Then i added together with 
Gerhard Stoll translations to english. The translator compares it also 
with the ATARI Compendium. So we where able to check possible false 
descriptions.

> But I'm here to learn more about the root of our beloved OS - Intel GEM 
> and GEMDOS (DOS Plus?).

Because of the same roots i also played a little bit with PC-GEM. I made 
bugfixes in RCS and set up my ohne GEM library.

GEMDOS was a little bit like MS DOS. Bur i am not aware, that GEMDOS is 
used as a base for other DOS operating systems. And the BIOS and XBIOS 
are hardware specific.

> btw nice website

Thanks.

Regards
Michael