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===== Input =====


In this section we learn how to get keyboard and mouse input.

==== Basic Mouse Example ====

Building on the Basic Bitmaps example, we change the box to move with the mouse.

<file c main.c>
#include <stdio.h>
#include <allegro5/allegro.h>
 
const float FPS = 60;
const int SCREEN_W = 640;
const int SCREEN_H = 480;
const int BOUNCER_SIZE = 32;
 
int main(int argc, char **argv)
{
   ALLEGRO_DISPLAY *display = NULL;
   ALLEGRO_EVENT_QUEUE *event_queue = NULL;
   ALLEGRO_TIMER *timer = NULL;
   ALLEGRO_BITMAP *bouncer = NULL;
   float bouncer_x = SCREEN_W / 2.0 - BOUNCER_SIZE / 2.0;
   float bouncer_y = SCREEN_H / 2.0 - BOUNCER_SIZE / 2.0;
   bool redraw = true;
 
   if(!al_init()) {
      fprintf(stderr, "failed to initialize allegro!\n");
      return -1;
   }
 
   if(!al_install_mouse()) {
      fprintf(stderr, "failed to initialize the mouse!\n");
      return -1;
   }

   timer = al_create_timer(1.0 / FPS);
   if(!timer) {
      fprintf(stderr, "failed to create timer!\n");
      return -1;
   }
 
   display = al_create_display(SCREEN_W, SCREEN_H);
   if(!display) {
      fprintf(stderr, "failed to create display!\n");
      al_destroy_timer(timer);
      return -1;
   }
 
   bouncer = al_create_bitmap(BOUNCER_SIZE, BOUNCER_SIZE);
   if(!bouncer) {
      fprintf(stderr, "failed to create bouncer bitmap!\n");
      al_destroy_display(display);
      al_destroy_timer(timer);
      return -1;
   }
 
   al_set_target_bitmap(bouncer);
 
   al_clear_to_color(al_map_rgb(255, 0, 255));
 
   al_set_target_bitmap(al_get_backbuffer(display));
 
   event_queue = al_create_event_queue();
   if(!event_queue) {
      fprintf(stderr, "failed to create event_queue!\n");
      al_destroy_bitmap(bouncer);
      al_destroy_display(display);
      al_destroy_timer(timer);
      return -1;
   }
 
   al_register_event_source(event_queue, al_get_display_event_source(display));
 
   al_register_event_source(event_queue, al_get_timer_event_source(timer));

   al_register_event_source(event_queue, al_get_mouse_event_source());

   al_clear_to_color(al_map_rgb(0,0,0));
 
   al_flip_display();
 
   al_start_timer(timer);
 
   while(1)
   {
      ALLEGRO_EVENT ev;
      al_wait_for_event(event_queue, &ev);
 
      if(ev.type == ALLEGRO_EVENT_TIMER) {
         redraw = true;
      }
      else if(ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
         break;
      }
      else if(ev.type == ALLEGRO_EVENT_MOUSE_AXES ||
              ev.type == ALLEGRO_EVENT_MOUSE_ENTER_DISPLAY) {

         bouncer_x = ev.mouse.x;
         bouncer_y = ev.mouse.y;
      }
      else if(ev.type == ALLEGRO_EVENT_MOUSE_BUTTON_UP) {
          break;
      }
 
      if(redraw && al_is_event_queue_empty(event_queue)) {
         redraw = false;
 
         al_clear_to_color(al_map_rgb(0,0,0));
 
         al_draw_bitmap(bouncer, bouncer_x, bouncer_y, 0);
 
         al_flip_display();
      }
   }
 
   al_destroy_bitmap(bouncer);
   al_destroy_timer(timer);
   al_destroy_display(display);
   al_destroy_event_queue(event_queue);
 
   return 0;
}</file>

=== Walk through ===

Much like previous examples we will only go over the new bits.

<code c>   if(!al_install_mouse()) {
      fprintf(stderr, "failed to initialize the mouse!\n");
      return -1;
   }</code>
Setup the mouse subsystem. **al_install_mouse** returns false if it fails, and we exit if that happens.

<code c>   al_register_event_source(event_queue, al_get_mouse_event_source());</code>
Register the mouse's event source with our event queue. Without this we won't get any mouse events.

<code c>      else if(ev.type == ALLEGRO_EVENT_MOUSE_AXES ||
              ev.type == ALLEGRO_EVENT_MOUSE_ENTER_DISPLAY) {

         bouncer_x = ev.mouse.x;
         bouncer_y = ev.mouse.y;
      }</code>
A **ALLEGRO_EVENT_MOUSE_AXES** event is generated when the mouse is moved by the user, and a **ALLEGRO_EVENT_MOUSE_ENTER_DISPLAY** is generated when ever the mouse enters the display. Here we update our box's position to the mouse position received.

<code c>      else if(ev.type == ALLEGRO_EVENT_MOUSE_BUTTON_UP) {
          break;
      }</code>
Should any mouse button be pressed, immediately exit.

That was pretty simple no?

==== Basic Keyboard Example ====

Building upon the Basic Bitmaps example, we will learn to use the keyboard events.

<file c main.c>
#include <stdio.h>
#include <allegro5/allegro.h>
 
const float FPS = 60;
const int SCREEN_W = 640;
const int SCREEN_H = 480;
const int BOUNCER_SIZE = 32;
enum MYKEYS {
   KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT
};

int main(int argc, char **argv)
{
   ALLEGRO_DISPLAY *display = NULL;
   ALLEGRO_EVENT_QUEUE *event_queue = NULL;
   ALLEGRO_TIMER *timer = NULL;
   ALLEGRO_BITMAP *bouncer = NULL;
   float bouncer_x = SCREEN_W / 2.0 - BOUNCER_SIZE / 2.0;
   float bouncer_y = SCREEN_H / 2.0 - BOUNCER_SIZE / 2.0;
   bool key[4] = { false, false, false, false };
   bool redraw = true;
   bool doexit = false;

   if(!al_init()) {
      fprintf(stderr, "failed to initialize allegro!\n");
      return -1;
   }
 
   if(!al_install_keyboard()) {
      fprintf(stderr, "failed to initialize the keyboard!\n");
      return -1;
   }

   timer = al_create_timer(1.0 / FPS);
   if(!timer) {
      fprintf(stderr, "failed to create timer!\n");
      return -1;
   }
 
   display = al_create_display(SCREEN_W, SCREEN_H);
   if(!display) {
      fprintf(stderr, "failed to create display!\n");
      al_destroy_timer(timer);
      return -1;
   }
 
   bouncer = al_create_bitmap(BOUNCER_SIZE, BOUNCER_SIZE);
   if(!bouncer) {
      fprintf(stderr, "failed to create bouncer bitmap!\n");
      al_destroy_display(display);
      al_destroy_timer(timer);
      return -1;
   }
 
   al_set_target_bitmap(bouncer);
 
   al_clear_to_color(al_map_rgb(255, 0, 255));
 
   al_set_target_bitmap(al_get_backbuffer(display));
 
   event_queue = al_create_event_queue();
   if(!event_queue) {
      fprintf(stderr, "failed to create event_queue!\n");
      al_destroy_bitmap(bouncer);
      al_destroy_display(display);
      al_destroy_timer(timer);
      return -1;
   }
 
   al_register_event_source(event_queue, al_get_display_event_source(display));
 
   al_register_event_source(event_queue, al_get_timer_event_source(timer));

   al_register_event_source(event_queue, al_get_keyboard_event_source());

   al_clear_to_color(al_map_rgb(0,0,0));
 
   al_flip_display();
 
   al_start_timer(timer);
 
   while(!doexit)
   {
      ALLEGRO_EVENT ev;
      al_wait_for_event(event_queue, &ev);
 
      if(ev.type == ALLEGRO_EVENT_TIMER) {
         if(key[KEY_UP] && bouncer_y >= 4.0) {
            bouncer_y -= 4.0;
         }

         if(key[KEY_DOWN] && bouncer_y <= SCREEN_H - BOUNCER_SIZE - 4.0) {
            bouncer_y += 4.0;
         }

         if(key[KEY_LEFT] && bouncer_x >= 4.0) {
            bouncer_x -= 4.0;
         }

         if(key[KEY_RIGHT] && bouncer_x <= SCREEN_W - BOUNCER_SIZE - 4.0) {
            bouncer_x += 4.0;
         }

         redraw = true;
      }
      else if(ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
         break;
      }
      else if(ev.type == ALLEGRO_EVENT_KEY_DOWN) {
         switch(ev.keyboard.keycode) {
            case ALLEGRO_KEY_UP:
               key[KEY_UP] = true;
               break;

            case ALLEGRO_KEY_DOWN:
               key[KEY_DOWN] = true;
               break;

            case ALLEGRO_KEY_LEFT: 
               key[KEY_LEFT] = true;
               break;

            case ALLEGRO_KEY_RIGHT:
               key[KEY_RIGHT] = true;
               break;
         }
      }
      else if(ev.type == ALLEGRO_EVENT_KEY_UP) {
         switch(ev.keyboard.keycode) {
            case ALLEGRO_KEY_UP:
               key[KEY_UP] = false;
               break;

            case ALLEGRO_KEY_DOWN:
               key[KEY_DOWN] = false;
               break;

            case ALLEGRO_KEY_LEFT: 
               key[KEY_LEFT] = false;
               break;

            case ALLEGRO_KEY_RIGHT:
               key[KEY_RIGHT] = false;
               break;

            case ALLEGRO_KEY_ESCAPE:
               doexit = true;
               break;
         }
      }
 
      if(redraw && al_is_event_queue_empty(event_queue)) {
         redraw = false;
 
         al_clear_to_color(al_map_rgb(0,0,0));

         al_draw_bitmap(bouncer, bouncer_x, bouncer_y, 0);
 
         al_flip_display();
      }
   }
 
   al_destroy_bitmap(bouncer);
   al_destroy_timer(timer);
   al_destroy_display(display);
   al_destroy_event_queue(event_queue);
 
   return 0;
}</file>

=== Walk-through === 

<code c>enum MYKEYS {
   KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT
};</code>
Define ourselves some key constants to use with our key state array.

<code c>bool key[4] = { false, false, false, false };</code>
Define our key state array. This is where we'll store the state of the keys we're interested in.

<code c>   bool doexit = false;</code>
Define a flag to short circuit our while loop.

<code c>   if(!al_install_keyboard()) {
      fprintf(stderr, "failed to initialize the keyboard!\n");
      return -1;
   }</code>
Initialize the keyboard subsystem. **al_install_keyboard** will return false if it fails, we exit if that happens.

<code c>   al_register_event_source(event_queue, al_get_keyboard_event_source());</code>
Register the keyboard event source with our event queue. Without this we will never get any keyboard events.

<code c>   while(!doexit)</code>
Change up our while loop to exit should **doexit** be true. Gives us a cheap way to exit.

<code c>         if(key[KEY_UP] && bouncer_y >= 4.0) {
            bouncer_y -= 4.0;
         }

         if(key[KEY_DOWN] && bouncer_y <= SCREEN_H - BOUNCER_SIZE - 4.0) {
            bouncer_y += 4.0;
         }

         if(key[KEY_LEFT] && bouncer_x >= 4.0) {
            bouncer_x -= 4.0;
         }

         if(key[KEY_RIGHT] && bouncer_x <= SCREEN_W - BOUNCER_SIZE - 4.0) {
            bouncer_x += 4.0;
         }</code>
Here we check to see if one of our keys are down, and move our box in the direction of the key press.

To save a bit of space and effort, we're going to go through both key events in parallel.

<code c>      else if(ev.type == ALLEGRO_EVENT_KEY_DOWN) {</code>
The **ALLEGRO_EVENT_KEY_DOWN** event is generated whenever a key is pressed. 

<code c>      else if(ev.type == ALLEGRO_EVENT_KEY_UP) {</code>
The **ALLEGRO_EVENT_KEY_UP** event is generated whenever a key is released.

<code c>         switch(ev.keyboard.keycode) {</code>
We switch on the **keycode** member of the keyboard event structure. The **keycode** member contains an integer mapping to an allegro keycode.

<code c>            case ALLEGRO_KEY_*:
               key[KEY_*] = true; || key[KEY_*] = false;
               break;</code>
With both the key press and release events, we store the state of the pressed key into our **key[]** array.

<code c>            case ALLEGRO_KEY_ESC:
               doexit = true;
               break;</code>
Here we set our **doexit** flag to true, to cause the loop to exit the next time through.

Whew. A bit longer than the mouse example, but still pretty simple.

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