[AL] WinAllegro - final screen locking mechanism

[Stefan S. <1S...@gm...>]

Hi,
I want to announce my final screen locking mechanism.
Because of the architecture of Windows, especially
DirectDraw, it is not possible to access the screen bitmap
all the time. To draw something you have to lock the screen
bitmap to get a pointer to it. After this you can access it
as usual. When you have finished you must unlock the screen
bitmap again. This is currently only needed for the screen
bitmap.
Because of this I have created two functions at the moment:
lock_screen and unlock_screen. To draw something onto the
screen bitmap you have to do the following:

lock_screen();
putpixel(screen, x, y, color);
unlock_screen();

Of cause you don't need this for every command. It would be
enough if you only use it around you drawing code one time.
To be able to allow memory bitmaps that are based on DirectX
surfaces it could be possible in the future that you have to
use the locking functions for them too. Because of this it
would be better to call the locking functions "lock_bitmap"
and "unlock_bitmap". This way you can easily use the to be
locked bitmap as argument:

lock_bitmap(screen);
...drawing code...
unlock_bitmap(screen);

or

lock_bitmap(double_buffer);
...drawing code...
unlock_bitmap(double_buffer);

DirectX allows the creation of bitmaps in the video memory
that are NOT visible on the screen. The advantage is that
many current chipsets provide an hardware accelerated blit
routine from VRAM to VRAM. A double buffering application
would get a nice speedup. For this a new function like
create_video_bitmap could be created.
Unfortunately Shawn has used the name lock_bitmap elsewhere.
Do you know a better unused name? Is lock_bitmap used in any
user programs or is it only used by Shawn? If the last is
true, I could rename Shawn's version to _lock_bitmap or
something similar.
Something important that I have to mention is that between a
lock and an unlock you are not allowed to use function other
than the Allegro drawing functions. Otherwise a complete
deadlock is possible because Windows isn't working while the
lock is active.
I think this approach is better the older one. It's very
flexible and allows direct memory access. In DosAllegro the
locking routine would be short stubs that do nothing.

Bye
  Stefan
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1Stein-Software - http://1Stein.home.pages.de -
1S...@gm...
         Everything is possible, at least in theory