This is an excellent synthesis, Warp!
Can you add it to the POV-Wiki? I think it could be useful for beginners.
;-)
Paolo

"Warp" wrote
> > Can you explain exactly in what macros and user defined function are
> > different, lease?
>
>   Macros are a lot more generic entities than functions. While a macro
> can be used as if it was a function (except in certain cases), it can be
> used for a lot more. For example, you can make a macro which creates an
> object (something which a user-defined function cannot do).
>   In a way, you can think about a macro as if it was a subroutine call
> in a programming language.
>
>   A user-defined function resembles a lot more a mathematical function:
> It takes numerical parameters and it returns a numerical value (based on
> mathematical operations performed on these input values), and it basically
> cannot do anything else. You cannot use a user-defined function for
example
> to create an object.
>
>   For example:
>
> #macro CreateSphere(Location, Radius)
>   sphere { Location, Radius }
> #end
>
>   This is not a mathematical function. It doesn't even return a numerical
> value. It just creates a sphere. Macros don't really have a return value
> per se.
>   Macros work almost like substitution macros in C: It's almost as if
> the macro call was substituted by the contents of the macro.
>
>   You can't do that with user-defined functions. These can only be used
> for calculating a mathematical operation, and the return value of such
> function is the result of the operation in question.
>
>   You can often simulate a function with a macro. For example:
>
> #macro Length(A, B, C)
>   sqrt(A*A+B*B+C*C)
> #end
>
>   This will work a lot like a function. You can call it like Length(1,2,3)
> (you can think about it as if the call in question is substituted by the
> contents of the macro).
>
>   That is basically the equivalent of:
>
> #define Length = function(A,B,C) { sqrt(A*A+B*B+C*C) };
>
>   Then what is the difference? Why have user-defined functions at all
> since macros can be used for the same thing?
>
>   For one, user-defined functions are a whole lot faster. If you need to
> call such a function millions of times, it's a whole lot faster to do it
> with a user-defined function than with a macro.
>
>   Secondly, user-defined functions can be used in some render-time
> features, more specifically isosurfaces and parametric surfaces, while
> macros cannot (macros are purely parse-time entities and they simply
> don't exist at render time).
>
> -- 
>                                                           - Warp

Post a reply to this message