=pod

=head1 NAME

SDL::Mixer::Effects - sound effect functions

=head1 CATEGORY

Mixer

=head1 METHODS

=head2 register

 SDL::Mixer::Effects::register( $channel, $effect_callback, $done_callback, $arg );

Hook a processor function into a channel for post processing effects. You may just be reading the data and displaying it, or you may be altering 
the stream to add an echo. Most processors also have state data that they allocate as they are in use, this would be stored in the C<$arg> data 
space. When a processor is finished being used, any function passed into C<$done_callback> will be called.

The effects are put into a linked list, and always appended to the end, meaning they always work on previously registered effects output.

Returns: Zero on errors, such as a nonexisting channel.

B<Note>: Passing MIX_CHANNEL_POST will register the C<$effect_callback> as an postmix effect.

B<Note>: Do not use this on a threaded perl. This will crash.

Example:

 use SDL;
 use SDL::Mixer;
 use SDL::Mixer::Channels;
 use SDL::Mixer::Effects;
 use SDL::Mixer::Samples;
 
 my @last_stream        = ();
 my $echo_effect_func   = sub
 {
     my $channel  = shift;
     my $samples  = shift;
     my $position = shift;
     my @stream   = @_;
 
     my @stream2 = @stream;
     my $offset  = $samples / 2;
     for(my $i = 0; $i < $samples; $i+=2)
     {
         if($i < $offset)
         {
             if(scalar(@last_stream) == $samples)
             {
                 $stream2[$i]     = $stream[$i]     * 0.6 + $last_stream[$samples + $i - $offset]     * 0.4; # left
                 $stream2[$i + 1] = $stream[$i + 1] * 0.6 + $last_stream[$samples + $i - $offset + 1] * 0.4; # right
             }
         }
         else
         {
             $stream2[$i]     = $stream[$i]     * 0.6 + $stream[$i - $offset]     * 0.4; # left
             $stream2[$i + 1] = $stream[$i + 1] * 0.6 + $stream[$i - $offset + 1] * 0.4; # right
         }
     }
 
     @last_stream = @stream;
     return @stream2;
 };
 
 my $effect_done = sub
 {
     # you may do something here
 };
 
 SDL::Mixer::open_audio( 44100, SDL::Constants::AUDIO_S16, 2, 1024 );
 
 my $playing_channel = SDL::Mixer::Channels::play_channel( -1, SDL::Mixer::Samples::load_WAV('test/data/sample.wav'), -1 );
 SDL::Mixer::Effects::register($playing_channel, $echo_effect_func, $effect_done, 0);
 SDL::delay(2000);
 SDL::Mixer::Effects::unregister($playing_channel, $echo_effect_func);
 
 SDL::Mixer::close_audio();
 SDL::quit();

=head2 unregister

 SDL::Mixer::Effects::unregister( $channel, $effect_callback );

Remove the registered effect function from the effect list for channel.
If the channel is active the registered effect will have its C<$done_callback> function called, if it was specified in 
L<SDL::Mixer::Effects::register|SDL::Mixer::Effects/"register">.

Returns: Zero on errors, such as invalid channel, or effect function not registered on channel. 

B<Note>: Do not use this on a threaded perl. This will crash.

=head2 unregister_all

 SDL::Mixer::Effects::unregister_all( $channel );

This removes all effects registered to C<$channel>. If the channel is active all the registered effects will have their C<$done_callback> 
functions called, if they were specified in L<SDL::Mixer::Effects::register|SDL::Mixer::Effects/"register">.

Returns: Zero on errors, such as channel not existing. 

B<Note>: Do not use this on a threaded perl. This will crash.

=head2 set_post_mix

 SDL::Mixer::Effects::set_post_mix( $effect_callback, $arg );

Hook a processor function to the postmix stream for post processing effects. You may just be reading the data and displaying it, or you may be 
altering the stream to add an echo. This processor is never really finished, until you call it without arguments.
There can only be one postmix function used at a time through this method. Use L<SDL::Mixer::Effects::register|SDL::Mixer::Effects/"register"> 
with MIX_CHANNEL_POST to use multiple postmix processors.
This postmix processor is run AFTER all the registered postmixers set up by L<SDL::Mixer::Effects::register|SDL::Mixer::Effects/"register">. 

B<Note>: Do not use this on a threaded perl. This will crash.

=head2 set_distance

 SDL::Mixer::Effects::set_distance( $channel, $distance );

This effect simulates a simple attenuation of volume due to distance. The volume never quite reaches silence, even at max distance (C<255>).

NOTE: Using a distance of C<0> will cause the effect to unregister itself from channel. You cannot unregister it any other way, unless you use 
L<SDL::Mixer::Effects::unregister_all|SDL::Mixer::Effects/"unregister_all"> on the channel.

Returns: Zero on errors, such as an invalid channel, or if Mix_RegisterEffect failed. 

=head2 set_panning

 SDL::Mixer::Effects::set_panning( $channel, $left, $right );

This effect will only work on stereo audio. Meaning you called L<SDL::Mixer::open_audio|SDL::Mixer/"open_audio"> with 2 channels. 

B<Note>: Setting both left and right to 255 will unregister the effect from channel. You cannot unregister it any other way, unless you use 
L<SDL::Mixer::Effects::unregister_all|SDL::Mixer::Effects/"unregister_all"> on the channel.

B<Note>: Using this function on a mono audio device will not register the effect, nor will it return an error status.

Returns: Zero on errors, such as bad channel, or if L<SDL::Mixer::Effects::register|SDL::Mixer::Effects/"register"> failed. 

=head2 set_position

 SDL::Mixer::Effects::set_position( $channel, $angle, $distance );

This effect emulates a simple 3D audio effect. It's not all that realistic, but it can help improve some level of realism. By giving it the 
angle and distance from the camera's point of view, the effect pans and attenuates volumes.

C<$angle> is the direction in relation to forward from 0 to 360 degrees. Larger angles will be reduced to this range using angles % 360.

=over 4

=item *

0 = directly in front.

=item *

90 = directly to the right.

=item *

180 = directly behind.

=item *

270 = directly to the left.

=back

So you can see it goes clockwise starting at directly in front.

C<$distance> is C<0>(close/loud) to C<255>(far/quiet).

B<Note>: Using angle and distance of C<0>, will cause the effect to unregister itself from channel. You cannot unregister it any other way, 
unless you use L<SDL::Mixer::Effects::unregister_all|SDL::Mixer::Effects/"unregister_all"> on the channel.

Returns: Zero on errors, such as an invalid channel, or if L<SDL::Mixer::Effects::register|SDL::Mixer::Effects/"register"> failed. 

=head2 set_reverse_stereo

 SDL::Mixer::Effects::set_reverse_stereo( $channel, $flip );

If you pass C<1> to C<$flip> it simple reverse stereo, swaps left and right channel sound.

B<Note>: Using a flip of C<0>, will cause the effect to unregister itself from channel. You cannot unregister it any other way, unless you use 
L<SDL::Mixer::Effects::register|SDL::Mixer::Effects/"register"> on the channel. 

=head1 AUTHORS

See L<SDL/AUTHORS>.

=cut