BUG: Mask.overlap_mask

[Florian Krause]

Hello together,

Mask.overlap_mask does not what it is supposed to do. In the following
example, the two counts that are output should be the same. The second one
is the one from overlap_mask. I have no clue what goes wrong there, since
the results does not make any sense to me.

Please let me know how I can get the correct overlap mask in the case below.

Thanks,
Florian



import pygame

pygame.init()
pygame.display.init()
pygame.display.set_mode((800, 600))
s1 = pygame.Surface((100, 100)).convert_alpha()
s2 = pygame.Surface((200, 200)).convert_alpha()
s1.fill((0,0,0))
s2.fill((0,0,0))

m1 = pygame.mask.from_surface(s1)
m2 = pygame.mask.from_surface(s2)

print m1.overlap_area(m2, (-150, 50))
print m1.overlap_mask(m2, (-150, 50)).count()

[Russell Jones]

Might it be that one method assumes a position of (0,0) if none is set, and
the other does not? Is the result consistent for the unexpected result? If
not, that would suggest the values have not been initialised.

Russell

Post by Florian Krause
Hello together,
Mask.overlap_mask does not what it is supposed to do. In the following
example, the two counts that are output should be the same. The second one
is the one from overlap_mask. I have no clue what goes wrong there, since
the results does not make any sense to me.
Please let me know how I can get the correct overlap mask in the case below.
Thanks,
Florian
import pygame
pygame.init()
pygame.display.init()
pygame.display.set_mode((800, 600))
s1 = pygame.Surface((100, 100)).convert_alpha()
s2 = pygame.Surface((200, 200)).convert_alpha()
s1.fill((0,0,0))
s2.fill((0,0,0))
m1 = pygame.mask.from_surface(s1)
m2 = pygame.mask.from_surface(s2)
print m1.overlap_area(m2, (-150, 50))
print m1.overlap_mask(m2, (-150, 50)).count()
--
www.fladd.de - Homepage of Florian Krause

[Russell Jones]

The position of the surface shouldn't matter for a mask, though.

The value is curious. It also works with a positive offset. Perhaps these
will give some clues as to what's happening:

print [m1.overlap_mask(m2, (x, x)).count() for x in range(50)]
[10000, 9702, 9408, 9118, 8832, 8550, 8272, 7998, 7728, 7462, 7200, 6942,
6688, 6438, 6192, 5950, 5712, 5478, 5248, 5022, 4800, 4582, 4368, 4158,
3952, 3750, 3552, 3358, 3168, 2982, 2800, 2622, 2448, 2278, 2112, 1950,
1792, 1701, 1612, 1525, 1440, 1357, 1276, 1197, 1120, 1045, 972, 901, 832,
765]

prev = 10000
for y in [m1.overlap_mask(m2, (x, x)).count() for x in range(50)]:
print(prev - y, end=', ')
prev = y
0, 298, 294, 290, 286, 282, 278, 274, 270, 266, 262, 258, 254, 250, 246,
242, 238, 234, 230, 226, 222, 218, 214, 210, 206, 202, 198, 194, 190, 186,
182, 178, 174, 170, 166, 162, 158, 91, 89, 87, 85, 83, 81, 79, 77, 75, 73,
71, 69, 67,

You can file a bug at the link below, I couldn't find any existing issues
mentioning overlap_mask with a quick search.
https://bitbucket.org/pygame/pygame/issues

Russell

Post by Russell Jones
Might it be that one method assumes a position of (0,0) if none is set,
and the other does not? Is the result consistent for the unexpected result?
If not, that would suggest the values have not been initialised.
Russell

Post by Florian Krause
Hello together,
Mask.overlap_mask does not what it is supposed to do. In the following
example, the two counts that are output should be the same. The second one
is the one from overlap_mask. I have no clue what goes wrong there, since
the results does not make any sense to me.
Please let me know how I can get the correct overlap mask in the case below.
Thanks,
Florian
import pygame
pygame.init()
pygame.display.init()
pygame.display.set_mode((800, 600))
s1 = pygame.Surface((100, 100)).convert_alpha()
s2 = pygame.Surface((200, 200)).convert_alpha()
s1.fill((0,0,0))
s2.fill((0,0,0))
m1 = pygame.mask.from_surface(s1)
m2 = pygame.mask.from_surface(s2)
print m1.overlap_area(m2, (-150, 50))
print m1.overlap_mask(m2, (-150, 50)).count()
--
www.fladd.de - Homepage of Florian Krause