API(1)							User Contributed Perl Documentation						    API(1)

NAME

       PDL::API - making piddles from Perl and C/XS code

DESCRIPTION

       A simple cookbook how to create piddles manually.  It covers both the Perl and the C/XS level.  Additionally, it describes the PDL core
       routines that can be accessed from other modules. These routines basically define the PDL API. If you need to access piddles from C/XS you
       probably need to know about these functions.

SYNOPSIS

	 use PDL;
	 sub mkmypiddle {
	  ...
	 }

Creating a piddle manually from Perl
       Sometimes you want to create a piddle manually from binary data. You can do that at the Perl level.  Examples in the distribution include
       some of the IO routines. The code snippet below illustrates the required steps.

	  use Carp;
	  sub mkmypiddle {
	    my $class = shift;
	    my $pdl  = $class->new;
	    $pdl->set_datatype($PDL_B);
	    my @dims = (1,3,4);
	    my $size = 1;
	    for (@dims) { $size *= $_ }
	    $pdl->setdims([@dims]);
	    my $dref = $pdl->get_dataref();

	    # read data directly from file
	    open my $file, '<data.dat' or die "couldn't open data.dat";
	    my $len = $size*PDL::Core::howbig($pdl->get_datatype);
	    croak "couldn't read enough data" if
	      read( $file, $$dref, $len) != $len;
	    close $file;
	    $pdl->upd_data();

	    return $pdl;
	  }

Creating a piddle in C
       The following example creates a piddle at the C level.  We use the "Inline" module which is really the way to interface Perl and C these
       days. Note the use of the "PDL_INCLUDE", "PDL_TYPEMAP", "PDL_AUTO_INCLUDE" and "PDL_BOOT" functions that were imported from
       "PDL::Core::Dev". They are used in conjunction with an Inline Config call to ensure that the PDL typemap, the PDL include files and the PDL
       Core routines are found during compilation and later runtime execution.

	  use PDL::LiteF;
	  use PDL::Core::Dev;

	  $a = myfloatseq(); # exercise our C piddle constructor

	  print $a->info,"
";

	  # the reason for this config call is explained below
	  use Inline C => Config =>
	    INC 	  => &PDL_INCLUDE,  # make sure we find pdlcore.h etc
	    TYPEMAPS	  => &PDL_TYPEMAP,  # use the PDL typemap
	    AUTO_INCLUDE  => &PDL_AUTO_INCLUDE,  # global declarations and includes
	    BOOT	  => &PDL_BOOT;     # boot code to load the Core struct

	  use Inline C;
	  Inline->init; # useful if you want to be able to 'do'-load this script

	  __DATA__

	  __C__

	  static pdl* new_pdl(int datatype, PDL_Long dims[], int ndims)
	  {
	    pdl *p = PDL->pdlnew();
	    PDL->setdims (p, dims, ndims);  /* set dims */
	    p->datatype = datatype;	    /* and data type */
	    PDL->allocdata (p); 	    /* allocate the data chunk */

	    return p;
	  }

	  pdl* myfloatseq()
	  {
	    PDL_Long dims[] = {5,5,5};
	    pdl *p = new_pdl(PDL_F,dims,3);
	    PDL_Float *dataf = (PDL_Float *) p->data;
	    int i;

	    for (i=0;i<5*5*5;i++)
	      dataf[i] = i; /* the data must be initialized ! */
	    return p;
	  }

   Wrapping your own data into a piddle
       Sometimes you obtain a chunk of data from another source, for example an image processing library, etc.	All you want to do in that case is
       wrap your data into a piddle struct at the C level. Examples using this approach can be found in the IO modules (where FastRaw and FlexRaw
       use it for mmapped access) and the Gimp Perl module (that uses it to wrap Gimp pixel regions into piddles).  The following script
       demonstrates a simple example:

	  use PDL::LiteF;
	  use PDL::Core::Dev;
	  use PDL::Graphics::PGPLOT;

	  $b = mkpiddle();

	  print $b->info,"
";

	  imag1 $b;

	  use Inline C => Config =>
	    INC 	  => &PDL_INCLUDE,
	    TYPEMAPS	  => &PDL_TYPEMAP,
	    AUTO_INCLUDE  => &PDL_AUTO_INCLUDE,
	    BOOT	  => &PDL_BOOT;

	  use Inline C;
	  Inline->init;

	  __DATA__

	  __C__

	  /* wrap a user supplied chunk of data into a piddle
	   * You must specify the dimensions (dims,ndims) and
	   * the datatype (constants for the datatypes are declared
	   * in pdl.h; e.g. PDL_B for byte type, etc)
	   *
	   * when the created piddle 'npdl' is destroyed on the
	   * Perl side the function passed as the 'delete_magic'
	   * parameter will be called with the pointer to the pdl structure
	   * and the 'delparam' argument.
	   * This gives you an opportunity to perform any clean up
	   * that is necessary. For example, you might have to
	   * explicitly call a function to free the resources
	   * associated with your data pointer.
	   * At the very least 'delete_magic' should zero the piddle's data pointer:
	   *
	   *	 void delete_mydata(pdl* pdl, int param)
	   *	 {
	   *	   pdl->data = 0;
	   *	 }
	   *	 pdl *p = pdl_wrap(mydata, PDL_B, dims, ndims, delete_mydata,0);
	   *
	   * pdl_wrap returns the pointer to the pdl
	   * that was created.
	   */
	  typedef void (*DelMagic)(pdl *, int param);
	  static void default_magic(pdl *p, int pa) { p->data = 0; }
	  static pdl* pdl_wrap(void *data, int datatype, PDL_Long dims[],
			       int ndims, DelMagic delete_magic, int delparam)
	  {
	    pdl* npdl = PDL->pdlnew(); /* get the empty container */

	    PDL->setdims(npdl,dims,ndims); /* set dims	    */
	    npdl->datatype = datatype;	   /* and data type */
	    npdl->data = data;		   /* point it to your data */
	    /* make sure the core doesn't meddle with your data */
	    npdl->state |= PDL_DONTTOUCHDATA | PDL_ALLOCATED;
	    if (delete_magic != NULL)
	      PDL->add_deletedata_magic(npdl, delete_magic, delparam);
	    else
	      PDL->add_deletedata_magic(npdl, default_magic, 0);
	    return npdl;
	  }

	  #define SZ 256
	  /* a really silly function that makes a ramp image
	   * in reality this could be an opaque function
	   * in some library that you are using
	   */
	  static PDL_Byte* mkramp(void)
	  {
	    PDL_Byte *data;
	    int i;

	    if ((data = malloc(SZ*SZ*sizeof(PDL_Byte))) == NULL)
	      croak("mkramp: Couldn't allocate memory");
	    for (i=0;i<SZ*SZ;i++)
	      data[i] = i % SZ;

	    return data;
	  }

	  /* this function takes care of the required clean-up */
	  static void delete_myramp(pdl* p, int param)
	  {
	    if (p->data)
	      free(p->data);
	    p->data = 0;
	  }

	  pdl* mkpiddle()
	  {
	    PDL_Long dims[] = {SZ,SZ};
	    pdl *p;

	    p = pdl_wrap((void *) mkramp(), PDL_B, dims, 2,
			 delete_myramp,0); /* the delparam is abitrarily set to 0 */
	    return p;
	  }

The gory details
   The Core struct -- getting at PDL core routines at runtime
       PDL uses a technique similar to that employed by the Tk modules to let other modules use its core routines. A pointer to all shared core
       PDL routines is stored in the $PDL::SHARE variable.  XS code should get hold of this pointer at boot time so that the rest of the C/XS code
       can then use that pointer for access at run time. This initial loading of the pointer is most easily achieved using the functions
       "PDL_AUTO_INCLUDE" and "PDL_BOOT" that are defined and exported by "PDL::Core::Dev". Typical usage with the Inline module has already been
       demonstrated:

	  use Inline C => Config =>
	    INC 	  => &PDL_INCLUDE,
	    TYPEMAPS	  => &PDL_TYPEMAP,
	    AUTO_INCLUDE  => &PDL_AUTO_INCLUDE, # declarations
	    BOOT	  => &PDL_BOOT; 	# code for the XS boot section

       The code returned by "PDL_AUTO_INCLUDE" makes sure that pdlcore.h is included and declares the static variables to hold the pointer to the
       "Core" struct. It looks something like this:

	  print PDL_AUTO_INCLUDE;

	#include <pdlcore.h>
	static Core* PDL; /* Structure holds core C functions */
	static SV* CoreSV;	 /* Gets pointer to perl var holding core structure */

       The code returned by "PDL_BOOT" retrieves the $PDL::SHARE variable and initializes the pointer to the "Core" struct. For those who know
       their way around the Perl API here is the code:

	  print PDL_BOOT;

	  perl_require_pv ("PDL::Core"); /* make sure PDL::Core is loaded */
	  CoreSV = perl_get_sv("PDL::SHARE",FALSE);  /* SV* value */
	#ifndef aTHX_
	#define aTHX_
	#endif
	  if (CoreSV==NULL)
	    Perl_croak(aTHX_ "We require the PDL::Core module, which was not found");
	  PDL = INT2PTR(Core*,SvIV( CoreSV ));	/* Core* value */
	  if (PDL->Version != PDL_CORE_VERSION)
	    Perl_croak(aTHX_ "The code needs to be recompiled against the newly installed PDL");

       The "Core" struct contains version info to ensure that the structure defined in pdlcore.h really corresponds to the one obtained at
       runtime. The code above tests for this

	  if (PDL->Version != PDL_CORE_VERSION)
	    ....

       For more information on the Core struct see PDL::Internals.

       With these preparations your code can now access the core routines as already shown in some of the examples above, e.g.

	 pdl *p = PDL->pdlnew();

       By default the C variable named "PDL" is used to hold the pointer to the "Core" struct. If that is (for whichever reason) a problem you can
       explicitly specify a name for the variable with the "PDL_AUTO_INCLUDE" and the "PDL_BOOT" routines:

	  use Inline C => Config =>
	    INC 	  => &PDL_INCLUDE,
	    TYPEMAPS	  => &PDL_TYPEMAP,
	    AUTO_INCLUDE  => &PDL_AUTO_INCLUDE 'PDL_Corep',
	    BOOT	  => &PDL_BOOT 'PDL_Corep';

       Make sure you use the same identifier with "PDL_AUTO_INCLUDE" and "PDL_BOOT" and use that same identifier in your own code.  E.g.,
       continuning from the example above:

	 pdl *p = PDL_Corep->pdlnew();

   Some selected core routines explained
       The full definition of the "Core" struct can be found in the file pdlcore.h. In the following the most frequently used member functions of
       this struct are briefly explained.

       o    "pdl *SvPDLV(SV *sv)"

       o    "pdl *SetSV_PDL(SV *sv, pdl *it)"

       o    "pdl *pdlnew()"

	    "pdlnew" returns an empty pdl object that needs further initialization to turn it into a proper piddle. Example:

	      pdl *p = PDL->pdlnew();
	      PDL->setdims(p,dims,ndims);
	      p->datatype = PDL_B;

       o    "pdl *null()"

       o    "SV *copy(pdl* p, char* )"

       o    "void *smalloc(int nbytes)"

       o    "int howbig(int pdl_datatype)"

       o    "void add_deletedata_magic(pdl *p, void (*func)(pdl*, int), int param)"

       o    "void allocdata(pdl *p)"

       o    "void make_physical(pdl *p)"

       o    "void make_physdims(pdl *p)"

       o    "void make_physvaffine(pdl *p)"

       o    "void qsort_X(PDL_Xtype *data, int a, int b)" and "void qsort_ind_X(PDL_Xtype *data, int *ix, int a, int b)"

	    where X is one of B,S,U,L,F,D and Xtype is one of Byte, Short, Ushort, Long, Float or Double.

       o    "float NaN_float" and "double NaN_double"

	    These are constants to produce the required NaN values.

SEE ALSO

       PDL

       Inline

BUGS

       This manpage is still under development.  Feedback and corrections are welcome.

COPYRIGHT

       Copyright (c) 2001, Christian Soeller. All Rights Reserved.  This module is free software. It may be used, redistributed and/or modified
       under the same terms as PDL itself (see http://pdl.perl.org).

perl v5.12.1							    2009-10-17								    API(1)