[SDL] aalineRGBA problem

[Armin Steinhoff]

Tommi Kyntola <tommi.kyntola at ray.fi> schrieb am 14.06.2006 10:28:59:
> 
> Armin Steinhoff wrote:
> > "clemens kirchgatterer" <everslick at gmail.com> schrieb am 13.06.2006 13:41:16:
[ clip ..]
> >>
> >> then the MSB holds the alpha value of the pixel and the LSB the red
> >> colour channel. you get the idea?
> > 
> > Yes ... but does it mean I can define the pixel format in that way for my individual surfaces ?
> 
> I stand corrected, but my understanding is that yes. Those masks, and
> those alone once bpp has been defined, define how SDL and others (like
> SDL_gfx) use the per pixel bits when they draw onto that surface aswell
> as when they blit from that surface.

The example 'testbitmap.c' is using  mask values which are plain zero (LoadXBM)
That's confusing ....

> For example giving correct bitmasks and 32 bpp is all that it takes
> for a surface to be compatible with opengl.

OK

> (granted there are things like SRCALPHA and other flags that also have
>   effect here, but basically that's how it goes)
> 
> > What happens if I use mask values different from 0xFF?
> 
> Hmmm, someone with more insight on this might shed some more
> light on this, but my guess is that most sw assume that the
> bits in each mask are at least consecutive. Without that
> assumption it's a tad more difficult to calculate the range
> of each color.
> 
> In any case, wither it's supported or not to use masks like
> 0x00aaaa00, 0x55550000, 0xaa0000aa, 0x00005555, or not, I'd
> still call such masks "asking for it".

Seems to be related to R-, B-, G- nd Aloss ?

Sorry for these dumb questions again :)

Thanks

--Armin


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