=head1 NAME

SDLx::LayerManager - Extension for managing layers in a 2D world

=head1 CATEGORY 

Extension

=head1 SYNOPSIS

  use SDLx::Layer;
  use SDLx::LayerManager;
  
  use SDL::Image;
  use SDL::Surface;
  use SDL::Video;
  
  # creating layers
  my $layer1 = SDLx::Layer->new( SDL::Image::load('image1.png'), {userdata => '7'} );
  my $layer2 = SDLx::Layer->new( SDL::Image::load('image2.png'), 100, 200, {userdata => '42'} );
  
  # creating the manager that holds the layers
  my $layermanager = SDLx::LayerManager->new();
  $layermanager->add( $layer1 );
  $layermanager->add( $layer2 );
  
  my $display = # create your video surface here
  
  $layermanager->blit( $display );
  
  # accessing the layer at point(x,y)
  print( $layermanager->by_position( 150, 200 )->data->{userdata} ); # should print '42'

=head1 DESCRIPTION

SDLx::LayerManager is a package to handle a bunch of layers. A layer (see SDLx::Layer) is an SDL::Surface, the position of the surface on screen and some additional information.

The layermanager gives you the opportunity to obtain the layer at a given point on screen and get the layers that are ahead or behind a layer.

You will even be able to attach one or more layers to the mouse, e.g. for simulation some drag&drop functionality.

=head1 METHODS

=head2 new

  my $layermanager = SDLx::LayerManager->new();

This creates your layermanager object. It doesn't take any parameters.

=head2 add

  $layermanager->add( $layer );
  $layermanager->add( SDLx::Layer->new( $surface, $x, $y, $options ) );

Call C<add> to push an SDLx::Layer object to the layermanager.

=head2 layers

  my @layers = @{ $layermanager->layers };
  my $first_layer = $layermanager->layers->[0];

The method C<layers> returns all layers that were added before.

=head2 layer

  my $layer = $layermanager->layer( $index );

To obtain only one layer at index C<$index> use this function. C<$index> ranges from C<0> to C<length - 1>.

=head2 length

  my $length = $layermanager->length();

This method returns the count of the added layers.

=head2 blit

  $layermanager->blit( $surface );

This method blits all layers to the surface (e.g. your video surface).

=head2 by_position

  my $layer = $layermanager->by_position( $x, $y );

C<by_position> returns the C<SDLx::Layer> object at point C<$x $y>, which is not fully transparent at this pixel.

=head2 ahead

  my @layers = @{ $layermanager->ahead( $index ) };

This method returns all layers that are ahead of the given layer indicated by C<$index>.
Ahead means that a layer has a higher z-index and is blitted over the given layer.

B<Note>: This method doesn't check for transparency. This will change in future versions.

=head2 behind

  my @layers = @{ $layermanager->behind( $index ) };

This method returns all layers that are behind of the given layer indicated by C<$index>.
Behind means that a layer has a lower z-index and is blitted before the given layer.

B<Note>: This method doesn't check for transparency. This will change in future versions.

=head2 attach

  $layermanager->attach( $layer,  $x, $y );
  $layermanager->attach( @layers, $x, $y );

This function makes the given layer(s) sticky to the mouse. If you move the mouse the layer(s) will follow.
The layermanager blits these layers at last, so they will appear on top of all layers.

C<$x> and C<$y> should be set to the coords of the mouse, e.g. the coords of the mouse click.
If you omit C<$x> and C<$y> the layermanager obtains them via SDL::Events::get_mouse_state.

B<Note>: The z-index is not changed for the given layers.

=head2 detach_xy

  $layermanager->detach_xy( $x, $y );

C<detach_xy> detaches the previously attached layers to the given coords. The upper left corner of the backmost layer will be at C<$x> and C<$y>.
The other layers are positioned relative to the backmost layer just like before.

=head2 detach_back

  $layermanager->detach_back( );

C<detach_back> detaches the previously attached layers back to the position where they were attached.

=head2 foreground

  $layermanager->foreground( $layer );
  $layermanager->foreground( @layers );

This method moves the given layer(s) to the foreground so that they are blitted on top of the other layers.

=head1 BUGS

Report at sdlperl.ath.cx

=head1 SUPPORT

#sdl irc.perl.org

=head1 AUTHORS

See L<SDL/AUTHORS>.

=head1 COPYRIGHT

This program is free software; you can redistribute
it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the
LICENSE file included with this module.


=head1 SEE ALSO

perl(1), SDL(2).

=cut