[cairo] Cleaning up cairo-features.h

[Owen Taylor]

On Fri, 2005-05-06 at 23:48 -0400, Carl Worth wrote:
> For some time, the definitions in cairo-features.h have bugged me a
> bit. With what we've had, if one wanted to test for the presence of a
> backend, (say xlib), then one would use:
> 
> 	#ifdef CAIRO_HAS_XLIB_SURFACE
> 
> and in the (basically useless) case of testing for the absence:
> 
> 	#ifdef CAIRO_HAS_NO_XLIB_SURFACE
> 
> and this achieved by a simple #define for one macro or the other in
> cairo-features.h.
> 
> I think that the macros would be much more readable if used as:
> 
> 	#if CAIRO_HAS_XLIB_SURFACE
> 
> which consequently means they should be defined unconditionally, but
> to either a 1 or a 0 to indicate presence or absence.

Is there really a benefit from deviating from the standard 
of:

 #define CAIRO_HAS_XLIB_SURFACE 1

vs.

 /* Nothing */

In addition to being standard, that allows all four of:

 #if CAIRO_HAS_XLIB_SURFACE
 #if !CAIRO_HAS_XLIB_SURFACE
 #ifdef CAIRO_HAS_XLIB_SURFACE
 #ifndef CAIRO_HAS_XLIB_SURFACE

While with the definition you propose above, the #ifdef and
#ifndef don't work. (Silently do the wrong thing)

Regards,
						Owen

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