Getting keystrokes for display high scores

Getting keystrokes for display high scores

Eric Johnson

Member #14,841

January 2013

Hey there. Is there a better way to get the key a user typed and save it to a string than to use al_keycode_to_name? As a test, I want to create a high score table that saves the user's name. This is what I've got so far:

#SelectExpand
   1#include <string>
   2#include <iostream>
   3
   4#include <allegro5/allegro.h>
   5#include <allegro5/allegro_font.h>
   6
   7using std::cout;
   8using std::string;
   9
  10void checkReturn(const bool condition) {
  11
  12  if (!condition) {
  13
  14    cout << "Error: something failed.\n";
  15
  16    exit(EXIT_FAILURE);
  17  }
  18}
  19
  20int main(void) {
  21
  22  // Initialize Allegro and addons.
  23  checkReturn(al_init());
  24  checkReturn(al_init_font_addon());
  25  checkReturn(al_install_keyboard());
  26
  27  ALLEGRO_TIMER *timer;
  28  ALLEGRO_DISPLAY *display;
  29  ALLEGRO_EVENT_QUEUE *event_queue;
  30
  31  // Create events.
  32  checkReturn((timer = al_create_timer(1.0 / 60.0)));
  33  checkReturn((display = al_create_display(720, 480)));
  34  checkReturn((event_queue = al_create_event_queue()));
  35
  36  // Register events.
  37  al_register_event_source(event_queue, al_get_keyboard_event_source());
  38  al_register_event_source(event_queue, al_get_timer_event_source(timer));
  39  al_register_event_source(event_queue, al_get_display_event_source(display));
  40
  41  al_start_timer(timer);
  42
  43  bool render = true;
  44  bool running = true;
  45
  46  // Whatever the user types will be saved to this string.
  47  string name = "";
  48
  49  // Use the built-in font, as it's easiest to use.
  50  ALLEGRO_FONT *font = al_create_builtin_font();
  51
  52  // Blow up the screen 500% to accommodate for the small font (above).
  53  ALLEGRO_TRANSFORM transform;
  54  al_identity_transform(&transform);
  55  al_scale_transform(&transform, 5, 5);
  56  al_use_transform(&transform);
  57
  58  while (running) {
  59
  60    ALLEGRO_EVENT event;
  61
  62    al_wait_for_event(event_queue, &event);
  63
  64    if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
  65
  66      // The window was closed; break the loop and end the program.
  67      running = false;
  68    }
  69    else if (event.type == ALLEGRO_EVENT_KEY_DOWN) {
  70
  71      switch (event.keyboard.keycode) {
  72
  73        case ALLEGRO_KEY_SPACE:
  74
  75          // Add a space to the string.
  76          name += " ";
  77        break;
  78
  79        case ALLEGRO_KEY_BACKSPACE:
  80
  81          if (name.length() > 0) {
  82
  83            // Remove the last character from the string.
  84            name.erase(name.end() - 1, name.end());
  85          }
  86        break;
  87
  88        default:
  89
  90          // Add whatever the user typed to the string.
  91          name += al_keycode_to_name(event.keyboard.keycode);
  92        break;
  93      }
  94    }
  95    else if (event.type == ALLEGRO_EVENT_TIMER) {
  96
  97      render = true;
  98    }
  99
 100    if (render && al_is_event_queue_empty(event_queue)) {
 101
 102      render = false;
 103
 104      al_clear_to_color(al_map_rgb(255, 255, 255));
 105
 106      al_draw_text(font, al_map_rgb(255, 0, 0), 720 / 2 / 5, 16, ALLEGRO_ALIGN_CENTER, "What's your name?");
 107
 108      // Draw text that user entered.
 109      al_draw_textf(font, al_map_rgb(255, 0, 0), 720 / 2 / 5, 480 / 2 / 5, ALLEGRO_ALIGN_CENTER, "%s", name.c_str());
 110
 111      al_flip_display();
 112    }
 113  }
 114
 115  // Free up memory.
 116  al_destroy_font(font);
 117  al_destroy_timer(timer);
 118  al_destroy_display(display);
 119  al_destroy_event_queue(event_queue);
 120
 121  return 0;
 122}

The above is self-explanatory, but it takes the user's keystrokes and saves it to a string named "name", then displays it as the user types. The problem with the above, however, is that it saves shift keys and caps lock (and others) as "SHIFT_*" and "CAPS_LOCK", which isn't what I want.

What's a better way to just get alphanumeric input and to ignore all the rest without writing a bunch of if statements to continue for each?

Thanks in advance.

Edgar Reynaldo

Major Reynaldo

May 2007

Monitor the event queue for ALLEGRO_EVENT_KEY_CHAR events and store their keycode in a string.

http://liballeg.org/a5docs/trunk/events.html#allegro_event_key_char

http://liballeg.org/a5docs/trunk/keyboard.html#key-codes

http://liballeg.org

do {

   ALLEGRO_EVENT ev;
   al_wait_for_event(queue , &ev);
   if (ev.type == ALLEGRO_EVENT_KEY_CHAR) {
      if (ev.keyboard.keycode >= ALLEGRO_KEY_A && ev.keyboard.keycode <= ALLEGRO_KEY_Z) {
          name += 'a' += (ev.keyboard.keycode - ALLEGRO_KEY_A);
      }
      if (ev.keyboard.keycode >= ALLEGRO_KEY_0 && ev.keyboard.keycode <= ALLEGRO_KEY_9) {
          name += '0' + (ev.keyboard.keycode - ALLEGRO_KEY_0)
      }
   }

} while (!al_is_event_queue_empty(queue));

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King Piccolo will make it so Then I could just flip it with some sweet, sweet matrix math. In either case, I’ll ride this wagon until the wheels fall off. Thanks to those that keep it running

Eric Johnson

Member #14,841

January 2013

That worked like a charm, Edgar. Thanks a bunch.

Could you explain the significance of 'a' and '0'? I noticed that changing 'a' to 'A' results in capturing the upper-case version of letters. Does this have something to do with encoding the characters?

torhu

Member #2,727

September 2002

A character literal is just a number

---
Smokin' Guns - spaghetti western FPS action

Edgar Reynaldo

Major Reynaldo

May 2007

A traditional 'char' literal is just an ASCII number from -128 to 127. I'm taking advantage of the fact that the distance between ev.keyboard.keycode and ALLEGRO_KEY_A and ALLEGRO_KEY_0 is the same as the distance between 'a' and the character pressed and '0' and the character pressed.

ASCII chart :
Click Me!

Eric Johnson

Member #14,841

January 2013

Wow, that's slick! Thanks a bunch!