[SDL] Blit1to2 optimization

[Will Langford]

It'd be if extra mem eaten is good or not.  I know on my PDA, I'd be annoyed
at sizeof(int) * 64K being eaten up :) (given that lookup_map isn't typed,
it'd default to an int).

Generally, what you should probably do is convert your surface to the native
screen type.  This way it doesn't have to convert on every blit.

-Will

On 12/27/06, Gianni Trevisti <g.trevisti at gmail.com> wrote:
>
> hello all,
> I'm working on the porting of a game to a 16 bit/pixel embedded Linux box.
> This game is 8 bit/pixel and I noticed a lot of performance loss in the 8
> to 16
> bit/pixel conversion function of a SDL_Surface: Blit1to2
> I tried a modified version of Blit1to2 that uses a palette lookup table of
> 2
> entries built in this way:
>
> lookup_map[65536];
> Uint16 cc = 0;
> while (1) {
>     lookup_map[cc] = map[cc & 0x000000FF] | (map[(cc & 0x0000FF00) >> 8]
> << 16);
>     if (++cc == 0) break;
> }
>
> then, instead of working on every single source byte, as the original code
> do:
>     *(Uint16 *)dst = map[*src++];
>
> I work on a couple of bytes:
>     *(int *)dst = lookup_map[*(Uint16 *)src];
>
> I tried this version on my game and I had about five more frames (28 ->
> 32).
> Valgring tells me the new version is about two time faster, compared to
> the
> previous one. Obviously it requires 64K more space (for every palette
> table, but
> in my case I've only one of it) and the cache miss will increase (the new
> table
> is a lot bigger than the old one).
> Nethertheless, I gained 5 frames on a Geode processor, that has a _very_
> small
> cache.
>
> Do you thing it can be worth one's while to create a patch and submit it
> to this
> newsgroup? I ask this question because a lot of work must be done in order
> to
> transform my test code in a real patch :-)
>
> Gianni
>
>
> _______________________________________________
> SDL mailing list
> SDL at libsdl.org
> http://www.libsdl.org/mailman/listinfo/sdl
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.libsdl.org/pipermail/sdl-libsdl.org/attachments/20061227/717cf69d/attachment.html