Quoting Sven Neumann ([EMAIL PROTECTED]):
> Hi,
>
> Felix recently suggested a change to SET_ALPHA_PIXEL_RGB32 in
> DirectFB/src/gfx/generic/generic.h) that resulted in a nice
> performance improvement and that we are now using. I tried to
> do the same optimization to SET_ALPHA_PIXEL_RGB16 today and
> here's what I have come up with:
>
> #define SET_ALPHA_PIXEL_RGB16(d,r,g,b,a) \
> if (a) {\
> if (a == 0xFF) {\
> *(d) = (((r)&0xf8) << 8) | (((g)&0xfc) << 3) | (((b)&0xf8) >> 3);\
> }\
> else {\
> __u32 pixel;\
> __u8 s=((a)>>2)+1;\
> __u8 s1=(64-s);\
> \
> pixel = *(d);\
> pixel = (((((pixel & 0x0000f81f) * s1) + ((((r)<<8) | ((b)>>3)) * s)) &
>0x003e07c0) + \
> ((((pixel & 0x000007e0) * s1) + (((g)<<3) * s)) &
>0x0001f800)) >> 6; \
> *(d) = pixel;\
> }\
> }
>
> This code is indeed faster (>15%), but the output is not perfect
> (red bits seem to pollute the blue bits somehow). I have stared at
> this code for too long and can't find what I'm doing wrong here.
> Perhaps someone out there has an idea?
Red and blue channel have 5 bit, the green channel has 6 bit.
You have to treat them in a different way.
You made s have 6 bit, you also need one with 5 bit for red and blue channel.
The green then has to be shifted 6 to the right (as you already do),
but the red and blue have to shifted 5 to the right after being multiplied
by the 5 bit s.
--
Denis Oliver Kropp
( convergence )
( integrated media gmbh )
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