Mike Williams wrote:

> Wasn't it D. Stimits who wrote:
>
> >I'm very new to POVray, and using version 3.5 on Linux. In general, I'm
> >a C and C++ programmer, and am trying to do something in POVray that
> >would be a simple procedural call in C.
> >
> >I'm creating a scene of a set of nodes and paths between nodes for
> >creation of a picture something like the "traveling salesman" problem. A
> >path is traced through a series of locations (nodes) on given paths
> >(edges), finding the minimum path that visits each node exactly once. It
> >looks something like a 3D chess board with selected edges being placed
> >between squares, and some squares missing.
> >
> >I want to declare a global variable:
> >#declare Node_Center = < 0.0, 0.0, 0.0 >;
> >
> >And then prior to calling a macro inside of an object {} that renders a
> >node icon based on location of Node_Center, I want to call another macro
> >(such as "Translate_Left") that alters the value of Node_Center in one
> >direction (partially desired because of different handedness of POVray
> >axis and the input data axis), taking into account a scale. The problem
> >is I cannot seem to find a way to actually alter the content of
> >Node_Center that is not an error. I have to alter the value of
> >Node_Center before calling:
> >
> >object {
> >  Render_Node (Node_Center)
> >}
> >
> >Then the outside application can write the scene file based on something
> >like a series of:
> >
> >Translate_Left ()
> >object {
> >  Render_Node (Node_Center)
> >}
> >
> >Translate_Up ()
> >object {
> >  Render_Node (Node_Center)
> >}
> >
> >The application itself then merely knows to go left, right, up, or down,
> >and does not have to keep track of Node_Center, nor does the application
> >need to understand the difference in axis handedness or scaling between
> >data and POVray. Is it even possible to alter a global declaration like
> >this from outside of the object? If I can only do this from inside of an
> >object, how can I alter my global value prior to rendering the node's 
> icon?
> >
>
>
> I would have thought that the following syntax would work. What errors
> are you getting?
>
> #macro Translate_Left()
>   #declare Node_Center = Node_Center - x;
> #end
>
> #macro Translate_Up()
>   #declare Node_Center = Node_Center +y;
> #end
>
This works. Prior to this I made the mistake of not using declare after 
the variable was declared, a bit of a C-ism. But since it is really a 
macro expansion, it isn't a lot like C, the use of declare each and 
every modification of Node_Center does the job :)

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