[Pharo-dev] [squeak-dev] Re: Why Color rgb components are on 10 bits?

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Wed Dec 25 16:51:48 EST 2013


2013/12/25 Stéphane Ducasse <stephane.ducasse at inria.fr>

> Hello nicolas
>
> > I know the answer, we have 30 bits available for keeping the rgb
> instance variable as SmallInteger...
> > So it's the best we can do, while keeping an efficient format.
> >
> > But we are never using 10 bits for each component, for 32 bits image
> only 8 bit by color are used.
> > Since nowadays most Forms are 32 bits deep, this force useless
> conversions where we could have none.
> >
> > I see that Pharo 3.0 did unify Color and TranslucentColor by moving the
> alpha information in Color.
> > But did not change the rgb ComponentMax... Any reason why?
>
> No special reason. We just started to clean the code to understand it and
> avoid isKindOf: and because we thought
> that there is no need to have color and translucent colors anymore.
>
> > If we encoded rgb component on 8 bits, and reverted the alpha channel
> encoding, then we could have colors pre-encoded on 32 bits, but most using
> only 24 bits (because most are opaque) would be represented as SmallInteger.
> > But I don't know if it is really inter-operable, or more natural…
>
> Thanks for the discussion. Now do you have an idea about the speed gain?
>

Absolutely no idea.
BitBlt is rich enough (color maps or direct color components, depths,
endianness) to make this unpredictable by simply analyzing sender chain in
source code (it's too deep and convoluted).
The best way is to try it, but then one must choose a benchmark, and here
again it is a difficult decision, because maybe you didn't bench a path
that some other use intensively, how to guess without above analysis?

I saw those un-necessary mismatch while analyzing Graphics code...
By a principle of economy, I suggest to remove them.
Simplifying code a little bit is already a win.

Then, les petits ruisseaux font les grandes rivières, cumulated micro
optimizations may pay.

>
> > Juan followed another path for Cuis, opting for float components, which
> is another possibility, but our VM are not yet optimized for handling
> Floats...
> >
> > Thoughts?
>
>
>
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