[vtkusers] Low level access to Array data (OK, here's a patch suggestion)

[H.Vidal, Jr.]

So it would be nice to have pointer level access to things
like the vtkIntArray from tcl. This is handy for a situation where
array data will be loaded from acquisition device for analysis under vtk.
Anyway, this works in tcl for vtkCharArray like this:

vtkCharArray c
c SetNumberOfValues 100
set p [ c GetPointer 0]

Now $p will eval to the raw contents of c because a pointer to a char
array in tcl is how tcl thinks. So I guess this is why vtk developers
left GetPointer in methods supported for vtkCharArray under tcl.
However, as mentioned in other posts, this was not case for vtkIntArray.
I still have not figured out how a tcl implementation of a C++ object is
created, but I do know that, once created, you can patch and rebuild vtk
sources as in:

So vtkIntArrayTcl.cxx is the implementation of vtkIntArray under tcl.

if you patch it thusly (skip the copious comments, if you like...):

0a1,4
> // 12-Jun-03 HCV/TT
> //  1. add GetPointer Method functionality cribbed from existing
> //     vtkCharArrayTcl.cxx infrastructure
> //
327a332,359
> 
> // HCV/TT: add GetPointer handler
> //
>   if((!strcmp("GetPointer",argv[1])) && (argc==3))
>    {
>     char tempResult[100];
>     long temp0;
>     int *temp20;
>     error = 0;
> 
>     if(Tcl_GetInt(interp,argv[2],&tempi) != TCL_OK) error = 1;
>     temp0 = tempi;
>     if(!error)
>      {
>       temp20 = op->GetPointer(temp0);
>       if(temp20)
>        {
>         sprintf(tempResult,"%p",(void *)temp20);
>         Tcl_SetResult(interp, tempResult, TCL_VOLATILE);
>        }
>       else
>        {
>         Tcl_ResetResult(interp);
>        }
>       return TCL_OK;
>      }
>    }
> 
429a462
>     Tcl_AppendResult(interp,"  GetPointer\t with 1 args\n",NULL);

You can then do things like:

vtkIntArray i
i SetNumberOfValues 100
set p [ i GetPointer 0]
RxIntPointer $p

If RxIntPointer looks (in C) kind of like this:

void RxIntPointer(char *pcIn)
{
  int *pI;

  if(!sscan(pcIn,"%p",&pI))
   return;
  
  (now access raw data via *pI indirection)


presumably, if this kind of voodoo is applied to all vtk<thingy>Array
code, everywhere high speed I/O to raw data is possible. Woo hoo!!

have fun.

hv