Phil Clute <pcl### [at] tiacnet> wrote:
: I have to admit my experience with C programming is extremely
: limited. I guess I am confused as to what a "macro" is then.
: I assumed that constants were macros. What makes #define a 
: macro and #declare not a macro? They seem to serve the same
: purpose.

  A macro identifier is completely replaced by its value. For example:

#define PrintStatus printf("This is the status\n")

  Now you can type something like:

void Function(void)
{ PrintStatus;
}

  When parsing, the compiler substitutes the macro, so it converts it to:

void Function(void)
{ printf("This is the status\n");
}

  Povray #declared identifiers do _not_ work this way. For example, you can't
make this:

#declare MyTexture=texture { pigment { rgb 1 } }

sphere { 0,1 MyTexture }

  Povray does _not_ substitute the identifier "MyTexture" with its value, ie.
the result is _not_ this:

sphere { 0,1 texture { pigment { rgb 1 } } }

  Instead, povray will issue an error:

error: No matching } in sphere, texture identifier found instead.

  However, #macros work in povray exactly like #defines in C. You can make
this:

#macro MyTexture() texture { pigment { rgb 1 } } #end

sphere { 0,1 MyTexture() }

and it will work.
  You can make this same thing in C:

#define MyTexture() texture(whatever)

and when you type "MyTexture()" it will be substituted with
"texture(whatever)" (of course the parenthesis are obsolete here). You can
also give arguments the the #defined macro, just like to the povray
#macro.

  A better naming for the commands would be, for example, #let instead
of #declare and #define instead of #macro (although #macro is ok). Of
course it's too late now.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Nieminen Mika wrote:
>Instead, povray will issue an error:

>error: No matching } in sphere, texture identifier found instead.

Oh so that's why! I've tried to do exactly that, and that's the
error message I got.

Thanks
Phil
-- 
...coffee?...yes please! extra sugar,extra cream...Thank you.

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I was just looking through textures.inc and I found this:

#declare Shadow_Clouds =
texture {                          // The blue sky background for the
clouds 
    pigment { rgb <0.196078, 0.6, 0.8> }
    finish { ambient 0.7 diffuse 0 }
}
texture {                          // The upper part of the clouds
    pigment { FBM_Clouds }
    finish { ambient 1.0 diffuse 0 }
}
texture {                          // The darker underside of the clouds
    pigment { FBM_Clouds  translate -0.15*y }
    finish { ambient 0.6 diffuse 0 }
}


This gives the error message you said it would, so I wonder why it's in
there?

-- 
...coffee?...yes please! extra sugar,extra cream...Thank you.

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You have to use texture identifiers this way:

sphere { 0,1 texture { MyTexture } }

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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