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On Fri, 2010-08-13 at 10:42 +1000, Peter Wang wrote:
> >
> > But not sure, maybe we want this as a display flag instead of bitmap
> > flag? So I better ask here before I go ahead.
>
> Tentatively, I think the display flag would be better, otherwise we
> would need to call glTexParameter for every new source bitmap, right?
> Or does the flag apply to the destination bitmap?
It's in the per-texture state, so it's the other way around - we'd have
to change it every time if we keep it as per-display state. (It may be
different with D3D though. Since the HW is the same in both cases, I
guess it doesn't make much difference, performance-wise.)
> On a practical note, a lot of code is likely to call
> al_set_new_bitmap_flag(ALLEGRO_VIDEO_BITMAP) without or'ing it
> with the old flags.
>
Hm, true... but that just means our al_set_new_bitmap_flag function may
be hard to use correctly and having only a single flag available so far
made that not obvious. Maybe it should work like al_toggle_display_flag.
Anyway, about the filtering, my use case works like this. I have my
Mario sprite in my game who should scale up smoothly, so I set his
magnification filter to linear. I also have a small minimap which has
one pixel per tile and I display it scaled up like 8x or 16x. This can
*not* have a magnification filter or you'd just see something blurry.
So for that, it would be easier to set the filtering on a per-bitmap
basis - else I'd always have to change display filter state in my
drawing function.
> >
> > Also, we might want to add another flag:
> >
> > ALLEGRO_MIPMAP
> >
> > When you scale bitmaps out then that's almost a must to use. Mipmaps are
> > automatically updated with opengl es 1 when you use glTexImage2d so it's
> > just another flag to add to glTexParameter. (I don't know what happens
> > when you modify the texture with FBO, or how it works in other opengl
> > versions or in D3D though).
>
> Perhaps mipmaps should be on by default, and add the flag
> ALLEGRO_NO_MIPMAPS if you know you won't be scaling a particular
> bitmap.
>
They use twice the memory though and always require power-of-two sizes.
Also, drawing into bitmaps with a mipmap likely is very slow. So better
do it only when requested.
I only said "must use" while thinking of something like completely
scaling out a checkerboard... with mipmaps that will scale out naturally
(to a gray pixel) while without it will cause horrible flicker :P (no
matter if filtering is nearest or linear).
--
Elias Pschernig <elias.pschernig@xxxxxxxxxx>