oracular (3) SDLx::Controller.3pm.gz
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.