1screen(3)                       Allegro manual                       screen(3)
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NAME

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

10       #include <allegro.h>
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13       extern BITMAP *screen;
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DESCRIPTION

16       Global pointer to a bitmap, sized VIRTUAL_W x VIRTUAL_H. This  is  cre‐
17       ated  by set_gfx_mode(), and represents the hardware video memory. Only
18       a part of this bitmap  will  actually  be  visible,  sized  SCREEN_W  x
19       SCREEN_H.   Normally  this is the top left corner of the larger virtual
20       screen, so you can ignore the extra invisible virtual size of the  bit‐
21       map if you aren't interested in hardware scrolling or page flipping. To
22       move the visible window to other  parts  of  the  screen  bitmap,  call
23       scroll_screen().   Initially  the clipping rectangle will be limited to
24       the physical screen size, so if you want to draw onto a larger  virtual
25       screen  space outside this rectangle, you will need to adjust the clip‐
26       ping.
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28       For example, to draw a pixel onto the screen you would write:
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30          putpixel(screen, x, y, color);
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32       Or to implement a double-buffered system:
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34          /* Make a bitmap in RAM. */
35          BITMAP *bmp = create_bitmap(320, 200);
36          /* Clean the memory bitmap. */
37          clear_bitmap(bmp);
38          /* Draw onto the memory bitmap. */
39          putpixel(bmp, x, y, color);
40          /* Copy it to the screen. */
41          blit(bmp, screen, 0, 0, 0, 0, 320, 200);
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43       Warning: be very careful when using this pointer at the  same  time  as
44       any  bitmaps  created  by  the  create_video_bitmap() function (see the
45       description of this function for more detailed information). And  never
46       try to destroy it with destroy_bitmap().
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SEE ALSO

50       set_gfx_mode(3),      is_screen_bitmap(3),      create_video_bitmap(3),
51       scroll_screen(3)
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55Allegro                          version 4.4.2                       screen(3)
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