Task Description
Up to POV-Ray 3.7 RC7 it has not been possible so far to declare custom properties for POV-Ray’s objects, which would be especially useful for complex objects defined in include files.
Currently, if you want to have an object (e.g. a car) with certain variable parameters (e.g. colour, wheel rotation, ...) defined in an include file and the parameters set by a scene file which uses the include file, you have to choose one of the following approaches:
1. use a macro
#macro car(colour, wheelrot, ...)
...
#end
or, 2. check parameters declared before, e.g.
#declare car =
union {
#ifdef (colour)
#local colour_internal = colour;
#else
#local colour_internal = default_colour;
#end
}
The resulting object would be used in the following way:
#include "car.inc" // include file once
object {
car(rgb <1,0,0>, 0, ...) // macro approach
}
// other approach
#declare colour = rgb <1,0,0>;
#declare wheelrot = 0;
...
#include "car.inc" // include file every time you want to have a car object instance
object {
car
}
Needless to say, both approaches are not quite optimal.
The macro approach needs only one #include directive and name conflicts will (hopefully) not be a problem. However, one would have to look up the parameter order of the macro in the include file, in the worst case every time the macro is used.
The other approach needs as many #include directives as car objects shall be instantiated, there can arise name conflicts with other inculde files used in the scene, and a (potentially long) list of parameters has to be declared before each #include. On the other hand, with this approach for any value it is clear which information it gives, e.g. #declare colour = rgb <1,0,0> can easily be read as ‘set car colour to “red”‘.
My suggestion would be creating an SDL feature to
One step up could be to even declare object classes along with them.
This could look like this:
// include file code
class car { // alternatively (without classes) use #declare car = object { ...
property colour = rgb <1,0,0>; // with default colour
union {
...
}
}
// scene file code
car { // alternatively (without classes) use object { car ... }
colour rgb <0,0,1>
}
Note that this solution makes the declarations much more concise and easy-to-read. Especially in scenes with many includes and animation scenes where objects’ properties have to be manipulated according to sometimes complex functions, this would be very useful. Please also consider that such user-defined objects can have dozens of properties.
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