libsdl-perl 2.540-5 / usr / lib / perl5 / pods / SDLx / Controller.pod

=head1 NAME

SDLx::Controller - Handles the loops for events, movement and rendering

=head1 CATEGORY

Extension, Controller

=head1 SYNOPSIS

 use SDLx::Controller;

 # create our controller object
 my $app = SDLx::Controller->new;
 
 # we could also do:
 my $app = SDLx::App->new;
 # because App is also a controller

 # register some callbacks
 $app->add_event_handler( \&on_event );
 $app->add_move_handler( \&on_move );
 $app->add_show_handler( \&on_show );

 # run our game loop
 $app->run;

=head2 DESCRIPTION

The core of an SDL application/game is the main loop, where you handle events
and display your elements on the screen until something signals the end of
the program. This usually goes in the form of:

  while (1) {
      ...
  }

The problem most developers face, besides the repetitive work, is to ensure
the screen update is independent of the frame rate. Otherwise, your game will
run at different speeds on different machines and this is never good (old
MS-DOS games, anyone?).

One way to circumveint this is by capping the frame rate so it's the same no
matter what, but this is not the right way to do it as it penalizes better
hardware.

This module provides an industry-proven standard for frame independent
movement. It calls the movement handlers based on time (hi-res seconds) rather
than frame rate. You can add/remove handlers and control your main loop with
ease.

=head1 METHODS

=head2 new

 SDLx::Controller->new(
     dt    => 0.5,
     min_t => 0,
     event => $event_object,
 );

The C<dt> parameter specifies the length, in seconds, of a full movement step, and defaults to 0.1.
The C<dt> can  be anything and the game can still look the same.
It is only when you change the C<dt> without changing all the things in the movement step that are being multiplied by the first move argument that it will make a difference.
If you lower the C<dt>, everything will move faster than it did with it set higher, and vice-versa.
This is useful to add slo-mo and fast-forward features to the game, all you would have to do is change the C<dt>.

C<min_t> specifies the minimum time, in seconds, that has to accumulate before any move or show handlers are called, and defaults to 1 / 60.
Having the C<min_t> at 1 / 60 ensures that the controller can update the screen at a maximum of 60 times per second.
A "V-Sync" such as this is necessary to prevent video "tear", which occurs when the app is updating faster than the monitor can display.
Setting it to 0, as seen above, will let the app run as fast as it possibly can.

C<delay> specifies a loop delay in millisecs to place on the controller loop. B<NOTE:> Picking a good delay based on the needs can help reduce CPU load and pressure.

C<event> is a SDL::Event object that events going to the event callbacks are polled in to. It defaults to C<< SDL::Event->new() >>.

All parameters are optional.

Returns the new object.

=head2 run

After creating and setting up your handlers (see below), call this method to
activate the main loop. The main loop will run until C<stop> is called.

All hooked functions will be called during the main loop, in this order:

=over 4

=item 1. Events

=item 2. Movements

=item 3. Displaying

=back

Please refer to each handler below for information on received arguments.
Note that the second argument received by every callback is the C<SDLx::Controller> object.

=head2 stop

Returns from the C<run> loop.

=head2 pause

Attempts to pause the application with a call to C<SDL::Events::wait_event>. See L<SDL::Events>.

Takes 1 argument which is a callback. The application waits for the next event with C<wait_event>.
When one is received, it is passed to the callback as the first argument, along with the C<SDLx::Controller> object as the second argument.
If the callback then returns a true value, C<pause> will return.
If the callback returns a false value, C<pause> will repeat the process.

This can be used to easily implement a pause when the app loses focus:

 sub window {
     my ($e, $app) = @_;
     if($e->type == SDL_QUIT) {
         $app->stop;
         # quit handling is here so that the app
         # can be stopped while paused
     }
     elsif($e->type == SDL_ACTIVEEVENT) {
         if($e->active_state & SDL_APPINPUTFOCUS) {
             if($e->active_gain) {
                 return 1;
             }
             else {
                 $app->pause(\&window);
                 # recursive, but only once since the window
                 # can't lose focus again without gaining it first
             }
         }
     }
     return 0;
 }

Note: if you implement your own pause function, remember to update C<current_time> to the current time when the application unpauses.
This should be done with C<Time::HiRes::time>.
Otherwise, time will accumulate while the application is paused, and many movement steps will be called all at once when it unpauses.

Note 2: a pause will be potentially dangerous to the C<run> cycle (even if you implement your own) unless called by an C<event> callback.

=head2 paused

Returns 1 if the app is paused, undef otherwise.
This is only useful when used within code that will be run by C<pause>:

 sub pause {
     # press P to toggle pause
     
     my ($e, $app) = @_;
     if($e->type == SDL_QUIT) {
         $app->stop;
         # quit handling is here so that the app
         # can be stopped while paused
     }
     elsif($e->type == SDL_KEYDOWN) {
         if($e->key_sym == SDLK_p) {
             # We're paused, so end pause
             return 1 if $app->paused;
             
             # We're not paused, so pause
             $app->pause(\&pause);
         }
     }
     return 0;
 }

=head2 add_event_handler

Register a callback to handle events. You can add as many subs as you need.
Whenever a SDL::Event occurs, all registered callbacks will be triggered in
order. Returns the order queue number of the added callback.

The first argument passed to registered callbacks is the L<< SDL::Event >> object.
The second is the C<SDLx::Controller> object.

 sub stop {
    my ($event, $app) = @_;
    if($event->type == SDL_QUIT) {
        $app->stop;
    }
 }
 $app->add_event_handler(\&stop);

=head2 add_move_handler

Register a callback to update your objects. You can add as many subs as
you need. Returns the order queue number of the added callback.

All registered callbacks will be triggered in order for as many C<dt> as have happened between calls,
and once more for any remaining time less than C<dt>.
The first argument passed to the callbacks is the portion of the step, which will be 1 for a full step, and less than 1 for a partial step.
Movement values should be multiplied by this value.
The full steps correspond to the amount of C<dt> passed between calls, and the partial step corresponds to the call with the remaining time less than C<dt>.
The argument can be 0 if no time has passed since the last cycle. If you need to protect against this, set a C<min_t>, or put a C<< return unless $_[0] >> at the start of every move handler.

The second argument passed to the callbacks is the C<SDLx::Controller> object.
The third is the total amount of time passed since the call of C<run>.

You should use these handlers to update your in-game objects, check collisions, etc.
so you can check and/or update it as necessary.

 sub move_ball {
     my ($step, $app, $t) = @_;
     $ball->move_x( $ball->x_vel * $step );
     $ball->move_y( $ball->y_vel * $step );
 }

=head2 add_show_handler

Register a callback to render objects. You can add as many subs as you need.
Returns the order queue number of the added callback.
All registered callbacks will be triggered in order, once per run of the C<run> loop.

The first argument passed is the time, in seconds, since the previous call.
The second is the C<SDLx::Controller> object.

 sub show_ball {
     my ($delta, $app) = @_;
     $app->draw_rect(
         [ $ball->x, $ball->y, $ball->size, $ball->size ],
         $ball->colour
     );
 }

=head2 remove_move_handler( $index )

=head2 remove_event_handler( $index )

=head2 remove_show_handler( $index )

Removes the handler with the given index from the respective calling queue.

You can also pass a coderef.
The first coderef in the handler list that this matches will be removed.

Returns the removed handler.

=head2 remove_all_move_handlers

=head2 remove_all_event_handlers

=head2 remove_all_show_handlers

Removes all handlers from the respective calling queue.

=head2 remove_all_handlers

Quick access to removing all handlers at once.

=head2 dt

=head2 min_t

=head2 current_time

If an argument is passed, modifies the corresponding value to the argument.
C<dt> and C<min_t> will keep their old value until the beginning of the next C<run> cycle.

Returns the corresponding value.

=head1 AUTHORS

See L<SDL/AUTHORS>.

=head2 ACKNOWLEGDEMENTS

The idea and base for this module comes from Lazy Foo's L<< Frame Independent
Movement|http://www.lazyfoo.net/SDL_tutorials/lesson32/index.php >> tutorial,
and Glenn Fiedler's L<< Fix Your Timestep|http://gafferongames.com/game-physics/fix-your-timestep/ >> article on timing.