exflip.c from Allegro game programming library at Krugle

Show exflip.c syntax highlighted

/*
 *    Example program for the Allegro library, by Shawn Hargreaves.
 *
 *    This program moves a al_draw_circle across the al_screen, first with a
 *    double buffer and then using page flips.
 */


#include "allegro.h"



int main()
{
   AL_BITMAP *buffer;
   AL_BITMAP *page1, *page2;
   AL_BITMAP *active_page;
   int c;

   allegro_init();
   al_install_timer();

   /* Some platforms do page flipping by making one large al_screen that you
    * can then scroll, while others give you several smaller, unique
    * surfaces. If you use the al_create_video_bitmap() function, the same
    * code can work on either kind of platform, but you have to be careful
    * how you set the video mode in the first place. We want two pages of
    * 320x200 video memory, but if we just ask for that, on DOS Allegro
    * might use a VGA driver that won't later be able to give us a second
    * page of vram. But if we ask for the full 320x400 virtual al_screen that
    * we want, the call will fail when using DirectX drivers that can't do
    * this. So we try two different mode sets, first asking for the 320x400
    * size, and if that doesn't work, for 320x200.
    */
   if (al_set_gfx_mode(AL_GFX_AUTODETECT, 320, 200, 0, 400) != 0) {
      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);
   al_text_mode(-1);

   /* allocate the memory buffer */
   buffer = al_create_bitmap(AL_SCREEN_W, AL_SCREEN_H);

   /* first with a double buffer... */
   c = al_retrace_count+32;
   while (al_retrace_count-c <= AL_SCREEN_W+32) {
      al_clear_to_color(buffer, al_make_color(255, 255, 255));
      al_draw_circle_fill(buffer, al_retrace_count-c, AL_SCREEN_H/2, 32, al_make_color(0, 0, 0));
      al_printf_text(buffer, al_font_8x8, 0, 0, al_make_color(0, 0, 0),
		 "Double buffered (%s)", gfx_driver->name);
      al_blit(buffer, al_screen, 0, 0, 0, 0, AL_SCREEN_W, AL_SCREEN_H);
   }

   al_destroy_bitmap(buffer);

   /* now create two video memory bitmaps for the page flipping */
   page1 = al_create_video_bitmap(AL_SCREEN_W, AL_SCREEN_H);
   page2 = al_create_video_bitmap(AL_SCREEN_W, AL_SCREEN_H);

   if ((!page1) || (!page2)) {
      al_set_gfx_mode(AL_GFX_NONE, 0, 0, 0, 0);
      al_show_message("Unable to create two video memory pages\n");
      return 1;
   }

   active_page = page2;

   /* do the animation using page flips... */
   for (c=-32; c<=AL_SCREEN_W+32; c++) {
      al_clear_to_color(active_page, al_make_color(255, 255, 255));
      al_draw_circle_fill(active_page, c, AL_SCREEN_H/2, 32, al_make_color(0, 0, 0));
      al_printf_text(active_page, al_font_8x8, 0, 0, al_make_color(0, 0, 0),
		 "Page flipping (%s)", gfx_driver->name);
      al_show_video_bitmap(active_page);

      if (active_page == page1)
	 active_page = page2;
      else
	 active_page = page1;
   }

   al_destroy_bitmap(page1);
   al_destroy_bitmap(page2);

   return 0;
}

AL_END_OF_MAIN();
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