Re: [AD] Preparing for RC2

[Elias Pschernig <elias@xxxxxxxxxx>]

On Sat, 2005-08-27 at 01:07 -0700, Chris wrote:
> On Saturday 27 August 2005 12:02 am, Victor wrote:
> > No please! I ALWAYS show the mouse in memory bitmaps. With this technic
> > is easy to avoid flickering in cases where i don't care with
> > performance. And  when drawing the mouse in memory bitmaps i can easily
> > create some effects like multiple mouse cursors moving synchrounous
> > (for a game). Or create a mouse pointer in a moving bitmap.
> 
> It'd be better to just use
> draw_sprite(memory_bmp, mouse_sprite, mouse_x, mouse_y);
> before blitting to the screen. Showing the mouse on a memory bitmap causes the 
> mouse to be drawn to it over and over and over again where it'll never be 
> seen, and if you try to draw to the bitmap at the same time as the mouse 
> timer, you'll get undefinable behavior (mouse droppings and/or incomplete 
> draws).

Actually, there would be valid reasons to draw to a memory buffer, for
example:

blit(background, buffer, ...)
...
show_mouse(buffer)
while(1) {
    ...
    blit(buffer, screen, ...)
}

There's no (easy) way to use draw_sprite instead. But, we would need a
mutex around that last blit to be sure to keep the mouse drawer out of
it. freeze_mouse_flag wouldn't work, since it doesn't wait for the mouse
drawer to complete. acquire_bitmap wouldn't work as well, since memory
bitmaps have it as no-op.

So, in the end, I agree - with the current implementation we can't allow
it. But the reason is only technical.

The attached patch should disallow it - but I didn't think much about
consequences yet, so might not apply yet for RC2, it's only a trivial
change anyway.

-- 
Elias Pschernig

Index: src/mouse.c
===================================================================
RCS file: /cvsroot/alleg/allegro/src/mouse.c,v
retrieving revision 1.37
diff -r1.37 mouse.c
591a592,594
>    if (bmp && is_memory_bitmap(bmp))
>       return;
>