Mask acts as it if it was a solid box

Question

How can I make a mask that's alpha pixels don't collide?

I've tried everything, following tutorials, viewing other stackoverthrow questions/answers, nothing works. PLEASE SPECIFY THE PROBLEM AND THE SOLUTION.

Here's my code:

level = pygame.image.load(r'data\test lvl.png').convert_alpha()
rect = level.get_rect(center = (400,400))
levelmask = pygame.mask.from_surface(image)

This mask is just a solid box, drawing it yields a solid box. Here's the collision between the level and the player.

        offset = (X2, Y2)
        collide = levelmask.overlap(self.rect_mask, offset)
        print(offset)
        print(collide)
        if collide == None:
            collide = -1
        else:
            collide = 0
        return collide

And here's the code for the initialization of self.rect_mask.

        self.rect_mask = pygame.mask.Mask((75, 160))
        self.rect_mask.fill()

`mask.from_surface()` depends on the transparent pixel-data of the used image. Does your "test lvl1.png" have truly transparent pixels? — Kingsley, Jun 29 '22 at 23:21
The alpha value of transparent pixels should be 0 and of solids it should be 255 — Rabbid76, Jun 30 '22 at 04:55

score 2 · Answer 1 · answered Jun 30 '22 at 00:57

There seems to be nothing wrong with your code. I have incorporated elements of it into an example below.

So where could the issue be:

The "level" image has weird transparency (probably not, see comment above)
The levelmask used in the overlap() test is somehow different to the one created in the OP's example.
The offset is wrong somehow.
The 75 x 160 filled comparison mask is always too big to be "inside" the levelmask.

The example below uses the exact operations presented in the OP's example code. It works. A mask is created for the maze, where the non-wall parts are transparent. Another mask is created for the moving object (alien_*), also based on transparency.

Demo:

Code:

import pygame

# Window size
WINDOW_WIDTH  = 612
WINDOW_HEIGHT = 612
FPS           = 60

# background colours
INKY_BLACK = (   0,  0,  0 )
FIREY_RED  = ( 203, 49,  7 )


class Coordinate:
    def __init__( self, x, y=None ):
        if ( type(x) is tuple ):
            self.x = x[0]
            self.y = x[1]   # Pygame.Rect corner
        else:
            self.x = x
            self.y = y


### MAIN
pygame.init()
pygame.font.init()
SURFACE = pygame.HWSURFACE|pygame.DOUBLEBUF
window  = pygame.display.set_mode( ( WINDOW_WIDTH, WINDOW_HEIGHT ), SURFACE )
pygame.display.set_caption("Mask Example")

# Make some bitmaps with masks for collision
maze_image = pygame.image.load( "square_maze_10x10.png" ).convert_alpha()
maze_rect  = maze_image.get_rect()
maze_mask  = pygame.mask.from_surface( maze_image )

alien_image = pygame.image.load( "green_guy.png" ).convert_alpha()
alien_rect  = alien_image.get_rect()
alien_rect.topleft = ( 20, 20 )
alien_mask  = pygame.mask.from_surface( alien_image )


clock = pygame.time.Clock()
done  = False
while not done:

    # Handle user-input
    for event in pygame.event.get():
        if ( event.type == pygame.QUIT ):
            done = True

    # Handle continuous-keypresses
    keys = pygame.key.get_pressed()
    delta = Coordinate( 0,0 )
    if ( keys[pygame.K_UP] ):
        delta.y = -1
    elif ( keys[pygame.K_DOWN] ):
        delta.y = 1
    elif ( keys[pygame.K_LEFT] ):
        delta.x = -1
    elif ( keys[pygame.K_RIGHT] ):
        delta.x = 1
    # move according to keys
    alien_rect.x += delta.x 
    alien_rect.y += delta.y 

    # has the alien hit the walls use a Mask Check?
    background = INKY_BLACK
    if ( None != maze_mask.overlap( alien_mask, alien_rect.topleft ) ):   # <<-- Mask check here
        background = FIREY_RED

    # Repaint the screen
    window.fill( background )
    window.blit( maze_image, maze_rect )
    window.blit( alien_image, alien_rect )

    pygame.display.flip()
    clock.tick_busy_loop( FPS )

pygame.quit()

Resources:

See [Creating collisions between a Sprite and a list (that aren't sprites) in a Maze](https://stackoverflow.com/questions/68665022/creating-collisions-between-a-sprite-and-a-list-that-arent-sprites-in-a-maze) — Rabbid76, Jun 30 '22 at 04:55
I found the issue. I used "image" instead of "level" when creating the levelmask. — ThreeGordons, Jul 04 '22 at 18:20

Mask acts as it if it was a solid box

1 Answers1