excustom.c from Allegro game programming library at Krugle

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/*
 *    Example program for the Allegro library, by Shawn Hargreaves.
 *
 *    This program demonstrates how to write your own GUI objects.
 */


#include <time.h>

#include "allegro.h"



/* for the al_dialog_edit_proc() object */
char the_string[32] = "Change Me!";


/* the current time, for the clock object */
struct tm the_time;



/* helper function to draw a hand on the clock */
void draw_hand(AL_BITMAP *bmp, int value, int range, int v2, int range2, fixed length, int color)
{
   fixed angle;
   fixed x, y;
   int w, h;

   angle = ((al_int_to_fix(value) * 256) / range) + 
	   ((al_int_to_fix(v2) * 256) / (range * range2)) - al_int_to_fix(64);

   x = al_fix_mul(al_fix_cos(angle), length);
   y = al_fix_mul(al_fix_sin(angle), length);
   w = bmp->w / 2;
   h = bmp->h / 2;

   al_draw_line(bmp, w, h, w + al_fix_to_int(x*w), h + al_fix_to_int(y*h), color);
}



/* custom dialog procedure for the clock object */
int clock_proc(int msg, AL_DIALOG *d, int c)
{
   time_t current_time;
   struct tm *t;
   AL_BITMAP *temp;
   fixed angle, x, y;

   /* process the message */
   switch (msg) {

      /* initialise when we get a start message */
      case MSG_START:
	 /* store the current time */
	 current_time = time(NULL);
	 t = localtime(&current_time);
	 the_time = *t;

	 /* draw the clock background onto a memory bitmap */
	 temp = al_create_bitmap(d->w, d->h);
	 al_clear_to_color(temp, d->bg);

	 /* draw borders and a nobble in the middle */
	 al_draw_circle(temp, temp->w/2, temp->h/2, temp->w/2-1, d->fg);
	 al_draw_circle_fill(temp, temp->w/2, temp->h/2, 2, d->fg);

	 /* draw ticks around the edge */
	 for (angle=0; angle<al_int_to_fix(256); angle+=al_int_to_fix(256)/12) {
	    x = al_fix_cos(angle);
	    y = al_fix_sin(angle);
	    al_draw_line(temp, temp->w/2+al_fix_to_int(x*temp->w*15/32), 
		       temp->h/2+al_fix_to_int(y*temp->w*15/32), 
		       temp->w/2+al_fix_to_int(x*temp->w/2), 
		       temp->h/2+al_fix_to_int(y*temp->w/2), d->fg);
	 }

	 /* store the clock background bitmap in d->dp */
	 d->dp = temp;
	 break;

      /* shutdown when we get an end message */
      case MSG_END:
	 /* destroy the clock background bitmap */
	 al_destroy_bitmap(d->dp);
	 break;

      /* update the clock in response to idle messages */
      case MSG_IDLE:
	 /* read the current time */
	 current_time = time(NULL);
	 t = localtime(&current_time);

	 /* check if it has changed */
	 if ((the_time.tm_sec != t->tm_sec) ||
	     (the_time.tm_min != t->tm_min) ||
	     (the_time.tm_hour != t->tm_hour)) {
	    the_time = *t;

	    /* Redraw ourselves if the time has changed. Note that we have
	     * to turn the mouse off before doing this: the dialog manager
	     * turns it off whenever it sends us a draw message, but we
	     * are sending the message ourselves here so we are responsible 
	     * for making sure the mouse is off first. Also note the use of
	     * the al_object_message function rather than a simple recursive call
	     * to clock_proc(). This vectors the call through the function
	     * pointer in the dialog object, which allows other object
	     * procedures to hook it, for example a different type of clock
	     * could process the draw messages itself but pass idle messages
	     * on to this procedure.
	     */
	    al_show_mouse(NULL);
	    al_object_message(d, MSG_DRAW, 0);
	    al_show_mouse(al_screen);
	 }
	 break;

      /* draw the clock in response to draw messages */
      case MSG_DRAW:
	 /* draw onto a temporary memory bitmap to prevent flicker */
	 temp = al_create_bitmap(d->w, d->h);

	 /* copy the clock background onto the temporary bitmap */
	 al_blit(d->dp, temp, 0, 0, 0, 0, d->w, d->h);

	 /* draw the hands */
	 draw_hand(temp, the_time.tm_sec, 60, 0, 1, al_int_to_fix(9)/10, d->fg);
	 draw_hand(temp, the_time.tm_min, 60, the_time.tm_sec, 60, al_int_to_fix(5)/6, d->fg);
	 draw_hand(temp, the_time.tm_hour, 12, the_time.tm_min, 60, al_int_to_fix(1)/2, d->fg);

	 /* copy the temporary bitmap onto the al_screen */
	 al_blit(temp, al_screen, 0, 0, d->x, d->y, d->w, d->h);
	 al_destroy_bitmap(temp);
	 break; 
   }

   /* always return OK status, since the clock doesn't ever need to close 
    * the dialog or get the input focus.
    */
   return D_O_K;
}



AL_DIALOG the_dialog[] =
{
   /* (dialog proc)     (x)   (y)   (w)   (h)   (fg)  (bg)  (al_key) (flags)  (d1)                    (d2)  (dp)           (dp2) (dp3) */
   { al_dialog_clear_proc,      0,    0,    0,    0,    255,  0,    0,    0,       0,                      0,    NULL,          NULL, NULL  },
   { al_dialog_edit_proc,       32,   32,   256,  8,    255,  0,    0,    0,       sizeof(the_string)-1,   0,    the_string,    NULL, NULL  },
   { al_dialog_check_proc,      32,   64,   89,   13,   255,  0,    't',  0,       0,                      0,    "&Toggle Me",  NULL, NULL  },
   { clock_proc,        192,  64,   64,   64,   255,  0,    0,    0,       0,                      0,    NULL,          NULL, NULL  },
   { al_dialog_button_proc,     120,  160,  81,   17,   255,  0,    0,    D_EXIT,  0,                      0,    "Exit",        NULL, NULL  },
   { NULL,              0,    0,    0,    0,    0,    0,    0,    0,       0,                      0,    NULL,          NULL, NULL  }
};



int main()
{
   int item;

   allegro_init();
   al_install_keyboard(); 
   al_install_mouse();
   al_install_timer();
   if (al_set_gfx_mode(AL_GFX_SAFE, 320, 200, 0, 0) != 0) {
      al_set_gfx_mode(AL_GFX_NONE, 0, 0, 0, 0);
      al_show_message("Unable to set any graphic mode\n%s\n", al_error);
      return 1;
   }
   al_set_palette(al_desktop_palette);

   /* We set up colors to match al_screen color depth (in case it changed) */
   for (item = 0; the_dialog[item].proc; item++) {
      the_dialog[item].fg = al_make_color(0, 0, 0);
      the_dialog[item].bg = al_make_color(255, 255, 255);
   }

   al_do_dialog(the_dialog, -1);

   return 0;
}

AL_END_OF_MAIN();
See more files for this project here