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pods::SDLx::ControllerUser Contributed Perl Documentapods::SDLx::Controller(3)

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

       Extension, Controller

	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

       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.

	    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.

       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

       1. Events
       2. Movements
       3. Displaying

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

       Returns from the	"run" loop.

       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) {
		# 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 {
			# 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.

       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) {
		# 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
	    return 0;

       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

       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)	{

       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

       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	);

       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) =	@_;
		[ $ball->x, $ball->y, $ball->size, $ball->size ],

   remove_move_handler(	$index )
   remove_event_handler( $index	)
   remove_show_handler(	$index )
       Removes the handler with	the given index	from the respective calling

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

       Returns the removed handler.

       Removes all handlers from the respective	calling	queue.

       Quick access to removing	all handlers at	once.

       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.

       See "AUTHORS" in	SDL.

       The idea	and base for this module comes from Lazy Foo's Frame
       Independent Movement
       <> tutorial, and
       Glenn Fiedler's Fix Your	Timestep <
       physics/fix-your-timestep/> article on timing.

perl v5.32.0			  2020-08-30	     pods::SDLx::Controller(3)


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