Re: [AD] improvements on alpha blending...

[Javier González <xaviergonz@xxxxxxxxxx>]

Javier González writes:
>> We can keep it global. AFAIK, it can be shared in between various calls
>> to draw_trans_sprite, and should remain valid unless a call to
>> set_blender() was made.
>
> certainly, i was thinking of draw_trans_sprite, but it is
> true it can be done even better per each set_trans_blender call

>This is quite a dangerous optimisation, though, because building the table
>costs just as much as the current per-pixel blend, so it is only a win if
>you are drawing very large images, and could lose a huge amount of time if
>people are doing things like drawing clouds of 8x8 particles with a
>different alpha setting on each one (which is not such an unusual thing to
>do).

>To give consistently good performance, you'd have to keep both
>implementations, and only decide to use the precalculated table once a draw
>call decided that the area being blended was large enough for this to be a
>win. This adds a lot of complexity and extra house-keeping logic, since at
>the time set_trans_blender() gets called, there's no way to know what the
>subsequent usage will be. I'm not convinced that the performance win in the
>very-big-image case would be enough to justify all that extra work, and
>having to maintain two completely separate code paths.

Then why dont add it into the draw_trans_sprite?
if ((width * height) > 22000 pixels) use table
else dont use it

>I reckon that doing the blending on a per-line basis would give a good
speed
>boost, that would apply more equally in all situations and not need
multiple
>versions of the code.

true