Mail Archives: djgpp/1996/03/18/13:10:14
On Mon, 18 Mar 1996, A.Appleyard wrote:
> Does djgpp v2 still carry around a load of graphics drivers? Or does the
> (first graphics call in each run of a djgpp program) call some such interrupt
> as `AX=0x4f01, int10' to find what modes it has, and thus decide what DOS or
> VESA screen mode to use to represent each of the 9 djgpp screen modes?
> djgpp screen mode 7 is described as "biggest non-interlaced graphics". What
> is "non-interlaced" graphics? Why is non-interlacing-ness relevant? How do I
> find via `AX=0x4f01, int10' whether any particular screen mode is
> non-interlacing?
>
This is my first ever response to a news group so if I screwed
this up sorry. You can flame me.
I come from DOS-land, have worked in it about a decade. I am not
a specialist on DJGPP but if I understand what the non-interlaced means
it is the way that the video card stores and retrieves information for
the user. In non-interlaced mode all memory locations are stored
contiguously straight through. In interlaced ever other screen line is
contigous. In other words if you have a video buffer 64K in size the
first 32K contains every odd numbered line, and the second 32K is every
even numbered line. Or vice versa. I don't have a text handy, but I
think that CGA used that approach.
In case you think that this is stupid, it is now. Back then it
was to enable slow cards and monitors to only refresh half the screen at
refresh. If you are using someone elses graphics library you probably
don't care whether it is interlaced or not. If you are writing your own
library at the low level, you had better be ready to account for it.
Hope I helped.
"Never attribute to malice that which can
be more easily explained by stupidity."
- Hanlon's Razor
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