using System;

using sharpallegro;

namespace exflip
{
  unsafe class exflip : Allegro
  {
    static int Main()
    {
      // TODO: replace with BITMAP structure
      IntPtr buffer;
      IntPtr page1, page2;
      IntPtr active_page;
      int c;

      if (allegro_init() != 0)
        return 1;
      install_timer();
      install_keyboard();

      /* Some platforms do page flipping by making one large screen that you
       * can then scroll, while others give you several smaller, unique
       * surfaces. If you use the 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 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 (set_gfx_mode(GFX_AUTODETECT, 320, 200, 0, 400) != 0)
      {
        if (set_gfx_mode(GFX_AUTODETECT, 320, 200, 0, 0) != 0)
        {
          if (set_gfx_mode(GFX_SAFE, 320, 200, 0, 0) != 0)
          {
            set_gfx_mode(GFX_TEXT, 0, 0, 0, 0);
            allegro_message("Unable to set any graphic mode\n" + allegro_error);
            return 1;
          }
        }
      }

      set_palette(desktop_palette);

      /* allocate the memory buffer */
      buffer = create_bitmap(SCREEN_W, SCREEN_H);

      /* first with a double buffer... */
      clear_keybuf();
      c = retrace_count + 32;
      while (retrace_count - c <= SCREEN_W + 32)
      {
        clear_to_color(buffer, makecol(255, 255, 255));
        circlefill(buffer, retrace_count - c, SCREEN_H / 2, 32, makecol(0, 0, 0));
        textprintf_ex(buffer, font, 0, 0, makecol(0, 0, 0), -1,
          "Double buffered (" + gfx_driver.name + ")");
        blit(buffer, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);

        if (keypressed())
          break;
      }

      destroy_bitmap(buffer);

      /* now create two video memory bitmaps for the page flipping */
      page1 = create_video_bitmap(SCREEN_W, SCREEN_H);
      page2 = create_video_bitmap(SCREEN_W, SCREEN_H);

      // TODO: replace once implemented !operator on BITMAP
      if ((page1 == IntPtr.Zero) || (page2 == IntPtr.Zero))
      {
        set_gfx_mode(GFX_TEXT, 0, 0, 0, 0);
        allegro_message("Unable to create two video memory pages\n");
        return 1;
      }

      active_page = page2;

      /* do the animation using page flips... */
      clear_keybuf();
      for (c = -32; c <= SCREEN_W + 32; c++)
      {
        clear_to_color(active_page, makecol(255, 255, 255));
        circlefill(active_page, c, SCREEN_H / 2, 32, makecol(0, 0, 0));
        textprintf_ex(active_page, font, 0, 0, makecol(0, 0, 0), -1,
          "Page flipping (" + gfx_driver.name + ")");
        show_video_bitmap(active_page);

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

        if (keypressed())
          break;
      }

      destroy_bitmap(page1);
      destroy_bitmap(page2);

      return 0;
    }
  }
}