Paul St George wrote:
> So...
>
> print pygame.display.get_surface()
> gives
> <Surface(720x480x32 SW)>
>
> and
> print screen.get_flags()
> gives
> -2147483648
> To recap: this thread started with a question. How do I know whether
> DOUBLEBUF has been set with:
>
> screen = pygame.display.set_mode((720,480), pygame.DOUBLEBUF |
> pygame.FULLSCREEN)
flags = screen.get_flags()
if flags & pygame.DOUBLEBUF:
print("DOUBLEBUF has been set")
if flags & pygame.FULLSCREEN:
print("FULLSCREEN has been set")
See the pattern?
The easiest way to argue about flags is in binary notation. Every flag
corresponds to an integer with a single bit set, e. g.
HOT = 0b001
BLUE = 0b010
RIGHTEOUS = 0b100
You can combine the flags with bitwise or
hot_and_righteous = HOT | RIGHTEOUS # 0b101
and query them with bitwise and:
>>> if hot_and_righteous & HOT: print("hot")
...
hot
>>> if hot_and_righteous & BLUE: print("blue")
...
>>> if hot_and_righteous & RIGHTEOUS: print("righteous")
...
righteous
With your actual pygame flags it's very much the same. However, because
integers in Python are signed numbers like
-2147483648
may be puzzling, even when you display them in binary
>>> bin(-2147483648)
'-0b10000000000000000000000000000000'
You might think that only one flag is set because there is only one 1, but
the - sign corresponds to an "infinite" number of leading 1s.
If you know that the flags are stored (for example) in a 32bit integer you
can mask off these leading 1s and see the actual data more clearly:
>>> bin(-2147483648 & 0b11111111111111111111111111111111)
'0b10000000000000000000000000000000'
OK, so in this case it probably* was a single flag, but that's not always
the case:
>>> bin(-7)
'-0b111'
>>> bin(-7 & 0b11111111111111111111111111111111)
'0b11111111111111111111111111111001'
(*) What if the flags were stored in a 64bit integer?
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