=head1 NAME

Gimp::Pixel - how to operate on raw pixels.

***WARNING*** this manpage is no longer up-to-date. See
C<examples/map_to_gradient> for a simple raw-pixel-manipulating
plug-in. If you bug me enough I'll rewrite this document.

=head1 SYNOPSIS

  use Gimp;
  use PDL;		# to make sensible things with the pixels

  # Gimp::GDrawable	- The GDrawable structure
  # Gimp::Tile		- The Tile family of functions.
  # Gimp::PixelRgn	- The PixelRgn family of functions.

=head1 DESCRIPTION

You can access the pixels in a drawable through tiles or pixel regions. This
manpage explains how this is done in perl. All classes (Gimp::GDrawable,
Gimp::Tile, Gimp::PixelRgn) are available with and without the C<Gimp::> prefix.

=head1 GDRAWABLES

Well, you know drawables? (also known as PARAM_DRAWABLE or Gimp::Drawable)?
In the Gimp, drawables are things you can draw on: layers, channels or whole
images. While most functions named C<gimp_drawable_something> operate on
C<drawable_ID>s, some functions (notably the ones operating on raw pixel
data!) need a C<GDrawable> instead. Every drawable has a corresponding
C<GDrawable>, you can get it with the C<gimp_drawable_get> function:

 my $gdrawable = $drawable->get;

When the $gdrawable is destroyed, it is automatically flushed & detached, so
you don't need to do this yourself.

=head1 TILES

Tiles are the basic building blocks of all drawables. Each drawable consists
of a "grid" of tiles, each tile having the same size. The size of a tile is
always the same (it's hardcoded in your Gimp program).

The C<gimp_tile_width> and C<gimp_tile_height> functions return the current
width/height of a tile (at the moment, this is 64x64).

How do I get a tile? First, you have to grab a GDrawable structure. You can
get one from any drawable, by calling the C<get> function:

 my $gdrawable = $drawable->get;

in a sense, <$gdrawable> contains all tiles. Changes you make to them might
not be reflected in the image until you destroy this variable. (Thats the
reason I used "my" int he above example. Once $gdrawable gets out of scope,
the drawable in the gimp automatically gets updated).

To get access to a tile, you have to call C<get_tile> or C<get_tile2>.
C<get_tile> expects row/column numbers of the tile, while C<get_tile2>
expects pixel coordinates and will return the tile that pixel is in:

 my $tile = $gdrawable->get_tile2(1,75,60);

The C<data> method returns and sets the raw pixel data.

 $piddle = $tile->data;	# get the tile data as a piddle
 $piddle *= 0.5;	# do sth. with the pixels
 $tile->data($piddle);	# and modify the tile

=head1 PIXELREGIONS

C<PixelRgn>s are rectangular parts of a drawable. You can access single
pixels, rows, columns and rectangles within these regions. Don't expect me
to explain everything now, I don't understand the mechanism too well
myself..

How do I create a pixel region? First, you have to grab a GDrawable structure. You can
get one from any drawable, by calling the C<get> function:

 my $gdrawable = $drawable->get;

Now you can create as many PixelRgn structures as you want from
the C<GDrawable>:

 my $region = new PixelRgn($gdrawable,0,0,50,30,1,0);	# with "new"
 my $region = $gdrawable->pixel_rgn(0,0,50,30,1,0);	# or from a drawable

which method you choose is purely a question of style...

The following functions return packed pixel data (see L<Gimp::PDL> for an
easier way to manipulate on image data):

 $piddle = $region->get_pixel(45,60);		# return the pixel at (45|60)
 $piddle = $region->get_row(45,60,10);		# return ten horizontal pixels
 $piddle = $region->get_col(45,60,10);		# same but vertically
 $piddle = $region->get_rect(45,60,10,12);	# a 10x12 rectangle

To modify pixels, the dirty bit of the region must be set (I believe, but I
don't see the reason what the dirty bit in a region is for so I might be
wrong), and you can write pixel data to the region with the following
functions, each one corresponding to a get-function:

 $region->set_pixel($piddle,45,60);		# set pixel at (45|60)
 $region->set_row($piddle,45,60);		# set a row
 $region->set_col($piddle,45,60);		# set a column
 $region->set_rect($piddle,45,60);		# set a whole rectangle

Please note that (unlike the C functions they call), the size arguments
(width and/or height) are missing, they can be calculated from the piddle.

=head1 AUTHOR

Marc Lehmann <pcg@goof.com>

=head1 SEE ALSO

perl(1), Gimp(1).

=cut

