bionic (3) screen.3alleg4.gz

NAME

       screen - Global pointer to the screen hardware video memory. Allegro game programming library.

SYNOPSIS

       #include <allegro.h>

       extern BITMAP *screen;

DESCRIPTION

       Global  pointer  to  a  bitmap,  sized  VIRTUAL_W  x  VIRTUAL_H.  This  is created by set_gfx_mode(), and
       represents the hardware video memory. Only a part of this bitmap will actually be visible, sized SCREEN_W
       x  SCREEN_H.   Normally  this  is the top left corner of the larger virtual screen, so you can ignore the
       extra invisible virtual size of the bitmap if  you  aren't  interested  in  hardware  scrolling  or  page
       flipping.  To  move  the  visible  window  to  other  parts  of  the screen bitmap, call scroll_screen().
       Initially the clipping rectangle will be limited to the physical screen size, so if you want to draw onto
       a larger virtual screen space outside this rectangle, you will need to adjust the clipping.

       For example, to draw a pixel onto the screen you would write:

          putpixel(screen, x, y, color);

       Or to implement a double-buffered system:

          /* Make a bitmap in RAM. */
          BITMAP *bmp = create_bitmap(320, 200);
          /* Clean the memory bitmap. */
          clear_bitmap(bmp);
          /* Draw onto the memory bitmap. */
          putpixel(bmp, x, y, color);
          /* Copy it to the screen. */
          blit(bmp, screen, 0, 0, 0, 0, 320, 200);

       Warning:  be  very  careful  when  using  this  pointer  at  the  same time as any bitmaps created by the
       create_video_bitmap() function (see the description of this function for more detailed information).  And
       never try to destroy it with destroy_bitmap().

SEE ALSO

       set_gfx_mode(3alleg4), is_screen_bitmap(3alleg4), create_video_bitmap(3alleg4), scroll_screen(3alleg4)