[cairo] Use 8-bit colour values internally

[Behdad Esfahbod]

On Tue, 23 Aug 2005, MenTaLguY wrote:

> On Mon, 2005-08-22 at 23:37 -0400, Jason Dorje Short wrote:
>
> > #define COLOR_INT_TO_SHORT(c) ((c) << 8)
>
> If you're going to do that, it may as well be:
>
> #define COLOR_INT_TO_SHORT(c) (((c) << 8) | (c))

which happens to be

#define COLOR_INT_TO_SHORT(c) ((c) * 257)

> Which yields the expected 65535 for COLOR_INT_TO_SHORT(255),
> instead of 65280.

thanks to the (x+1) * (x-1) == (x*x-1).

> -mental

;)
--behdad