Provided by: libsdl-perl_2.546-3build1_amd64 
NAME
SDLx::Controller - Handles the loops for events, movement and rendering
CATEGORY
Extension, Controller
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;
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 circumvent 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.
METHODS
new
SDLx::Controller->new(
dt => 0.5,
min_t => 0,
event => $event_object,
);
The "dt" parameter specifies the length, in seconds, of a full movement step, and defaults
to 0.1. The "dt" can be anything and the game can still look the same. It is only when
you change the "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
"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 "dt".
"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 "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.
"delay" specifies a loop delay in millisecs to place on the controller loop. NOTE: Picking
a good delay based on the needs can help reduce CPU load and pressure.
"event" is a SDL::Event object that events going to the event callbacks are polled in to.
It defaults to "SDL::Event->new()".
All parameters are optional.
Returns the new object.
run
After creating and setting up your handlers (see below), call this method to activate the
main loop. The main loop will run until "stop" is called.
All hooked functions will be called during the main loop, in this order:
1. Events
2. Movements
3. Displaying
Please refer to each handler below for information on received arguments. Note that the
second argument received by every callback is the "SDLx::Controller" object.
stop
Returns from the "run" loop.
pause
Attempts to pause the application with a call to "SDL::Events::wait_event". See
SDL::Events.
Takes 1 argument which is a callback. The application waits for the next event with
"wait_event". When one is received, it is passed to the callback as the first argument,
along with the "SDLx::Controller" object as the second argument. If the callback then
returns a true value, "pause" will return. If the callback returns a false value, "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 {
$app->pause(\&window);
# recursive, but only once since the window
# can't lose focus again without gaining it first
}
}
}
return 0;
}
Note: if you implement your own pause function, remember to update "current_time" to the
current time when the application unpauses. This should be done with "Time::HiRes::time".
Otherwise, time will accumulate while the application is paused, and many movement steps
will be called all at once when it unpauses.
Note 2: a pause will be potentially dangerous to the "run" cycle (even if you implement
your own) unless called by an "event" callback.
paused
Returns 1 if the app is paused, undef otherwise. This is only useful when used within
code that will be run by "pause":
sub pause {
# press P to toggle pause
my ($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
$app->pause(\&pause);
}
}
return 0;
}
add_event_handler
Register a callback to handle events. You can add as many subs as you need. Whenever a
SDL::Event occurs, all registered callbacks will be triggered in order. Returns the order
queue number of the added callback.
The first argument passed to registered callbacks is the SDL::Event object. The second is
the "SDLx::Controller" object.
sub stop {
my ($event, $app) = @_;
if($event->type == SDL_QUIT) {
$app->stop;
}
}
$app->add_event_handler(\&stop);
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 "dt" as have happened
between calls, and once more for any remaining time less than "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 "dt" passed between calls, and the partial step
corresponds to the call with the remaining time less than "dt". The argument can be 0 if
no time has passed since the last cycle. If you need to protect against this, set a
"min_t", or put a "return unless $_[0]" at the start of every move handler.
The second argument passed to the callbacks is the "SDLx::Controller" object. The third
is the total amount of time passed since the call of "run".
You should use these handlers to update your in-game objects, check collisions, etc. so
you can check and/or update it as necessary.
sub move_ball {
my ($step, $app, $t) = @_;
$ball->move_x( $ball->x_vel * $step );
$ball->move_y( $ball->y_vel * $step );
}
add_show_handler
Register a callback to render objects. You can add as many subs as you need. Returns the
order queue number of the added callback. All registered callbacks will be triggered in
order, once per run of the "run" loop.
The first argument passed is the time, in seconds, since the previous call. The second is
the "SDLx::Controller" object.
sub show_ball {
my ($delta, $app) = @_;
$app->draw_rect(
[ $ball->x, $ball->y, $ball->size, $ball->size ],
$ball->colour
);
}
remove_move_handler( $index )
remove_event_handler( $index )
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.
remove_all_move_handlers
remove_all_event_handlers
remove_all_show_handlers
Removes all handlers from the respective calling queue.
remove_all_handlers
Quick access to removing all handlers at once.
dt
min_t
current_time
If an argument is passed, modifies the corresponding value to the argument. "dt" and
"min_t" will keep their old value until the beginning of the next "run" cycle.
Returns the corresponding value.
AUTHORS
See "AUTHORS" in SDL.
ACKNOWLEDGEMENTS
The idea and base for this module comes from Lazy Foo's Frame Independent Movement
<http://www.lazyfoo.net/SDL_tutorials/lesson32/index.php> tutorial, and Glenn Fiedler's
Fix Your Timestep <http://gafferongames.com/game-physics/fix-your-timestep/> article on
timing.