I'm working on matrix transformations using arrays, but nothing goes quite
as planned. The simplest example is transposing a 2d array:

////////////////////////////////////////////////////////////
#macro transp(array1)
     #local a1=dimension_size(array1,1);
     #local a2=dimension_size(array1,2);
     #local i=0;
     #local j=0;
     #declare temp1= array[a2][a1];
     #while (i<=a2-1)
           #while (j<=a1-1)
                  #declare temp1[i][j]=array1[j][i];
                  #local j=j+1;
           #end
           #local i=i+1;
     #end
#end

camera {location -8*z look_at 0}

light_source{<0,10,-10> rgb 1}

#declare ar1=array[3][2] {{1,0},{1,-1},{0,5}};
transp(ar1)
/////////////////////////////////////////////////////////////////

All good till now, I think, but when I try to visualise the result with the
following routine, I only get the first row. If I change the #while's in
the macro, so that i and j start from their highest values and go to 0,
only the last row is rendered. If I add a third dimension in the array,
only the values on a single spine are rendered. Any ideas on what I'm doing
wrong? I have
searched the newsgroup but I haven't seen many examples of nested #while
with arrays, so I'm inclined to think it's something to do with that. Pov
version is 3.61c for Windows.

///////////////////////////////////////////////////////////
#declare i1=0;
#declare j1=0;
union{
#while (i1<=dimension_size(temp1,1)-1)
      #while (j1<=dimension_size(temp1,2)-1)
             text{ttf "timrom.ttf"
                      str(temp1[i1][j1],1,0) 0.1,0 pigment {rgb 1}
              translate <(j1-1)*2,1-(i1-1),0>
              }
        #declare j1=j1+1;
        #end
    #declare i1=i1+1;
#end
}
//////////////////////////////////////////////////////////

Post a reply to this message

You are making the same mistake twice...
The initial value in your inner nested while loops
need to be set every time the inner loop executes.
Like this:

#local A = from#;
#while (A <= to#)
   #local B = from#;
   #while (B <= to#)
      ... process
      #local B = B + step#;
   #end
   #local A = A + step#;
#end

Post a reply to this message

Grassblade <nomail@nomail> wrote:
>      #local i=0;
>      #local j=0;
>      #declare temp1= array[a2][a1];
>      #while (i<=a2-1)
>            #while (j<=a1-1)

  When the execution gets to this point the second time, what do you
think the value of 'j' is?

-- 
                                                          - Warp

Post a reply to this message

"Tim Attwood" <tim### [at] comcastnet> wrote:
> You are making the same mistake twice...
> The initial value in your inner nested while loops
> need to be set every time the inner loop executes.
> Like this:
>
> #local A = from#;
> #while (A <= to#)
>    #local B = from#;
>    #while (B <= to#)
>       ... process
>       #local B = B + step#;
>    #end
>    #local A = A + step#;
> #end
Pfft, what a silly mistake! Would you believe I twiddled my code looking for
whatever was messing my code up for over an hour?
Anyway, thanks. It's working as it should now.

Post a reply to this message

Warp <war### [at] tagpovrayorg> wrote:
> Grassblade <nomail@nomail> wrote:
> >      #local i=0;
> >      #local j=0;
> >      #declare temp1= array[a2][a1];
> >      #while (i<=a2-1)
> >            #while (j<=a1-1)
>
>   When the execution gets to this point the second time, what do you
> think the value of 'j' is?
>
> --
>                                                           - Warp
Ehm, good point. <_<

Post a reply to this message