python - Collision between masks in pygame

Question

I have a problem with collisions in my game, spaceship's mask doesn't collide properly with a background and I believe that offset is a problem, however I'm not sure.

I've tried multiple collision techniques and checked a lot of answers to my problem, but none of them helped me.

import pygame as pg
import os

os.environ['SDL_VIDEO_WINDOW_POS'] = "%d,%d" % (2, 29)

pg.init()


def gameLoop():
    display_width = 1800
    display_height = 1000
    pg.display.set_caption("Kerbal Space Landing Simulator")
    clock = pg.time.Clock()
    display = pg.display.set_mode((display_width, display_height))
    sprsp = pg.image.load('C:/Users/PC/PycharmProjects/untitled/sprspaceship.png').convert_alpha()
    cosbg = pg.image.load('C:/Users/PC/PycharmProjects/untitled/cosmos bg.png').convert_alpha()
    done = False

class Spaceship:
    def __init__(self, x, y, mass):
        self.x = x
        self.y = y
        self.width = 139
        self.height = 106
        self.velx = 0
        self.vely = 0
        self.mass = mass
        self.color = (255, 255, 255)
        self.spr = sprsp
        self.fuel = 500
        self.mask = pg.mask.from_surface(self.spr)
        self.angle = 0
        self.changerot = 0

    def check_controls(self):
        if keys[pg.K_SPACE] and self.fuel > 0:
            if self.angle > 0:
                self.vely += 0.005 * (self.angle - 90)
                self.velx += -0.005 * self.angle
            else:
                self.vely += -0.005 * (self.angle + 90)
                self.velx += -0.005 * self.angle

            self.fuel += -3
        if keys[pg.K_LEFT] and self.angle < 90:
            self.angle += 2
        if keys[pg.K_RIGHT] and self.angle > -90:
            self.angle += -2

    def update_pos(self):
        self.vely += 0.01
        self.x += self.velx
        self.y += self.vely
        self.mask = pg.mask.from_surface(self.spr)

    def update_rotation(self):
        self.rspr = pg.transform.rotate(self.spr, self.angle)
        self.changerot -= self.angle

    def draw(self):
        if self.fuel > 0:
            pg.draw.rect(display, (255, 255, 255), (display_width - 100, 100 + 500 - self.fuel, 10, self.fuel), 0)
        display.blit(self.rspr, (int(self.x), int(self.y)))

        self.changerot = 0

class Terrain(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
        self.mask = pg.mask.from_threshold(display, (160, 160, 160))
        self.hitbox = pg.Rect(self.x, self.y, display_width, 500)
        self.ox = display_width // 2 - self.x // 2
        self.oy = display_height // 2 - self.y // 2

    def draw(self):
        pg.draw.rect(display, (160, 160, 160), (self.x, self.y, display_width, 500), 0)

spaceship = (Spaceship(500, 100, 1))
terrain = (Terrain(0, 800))

def redrawGameWindow():
    display.blit(cosbg, (0, 0))
    spaceship.draw()
    terrain.draw()
    pg.display.update()

def check_for_collisions():
    offset = (int(spaceship.x - terrain.ox), int(spaceship.y - terrain.oy))
    print(offset)
    print(spaceship.mask.overlap(terrain.mask, offset))
    return spaceship.mask.overlap(terrain.mask, offset)
    # return spaceship.hitbox.colliderect(terrain.hitbox)
    # return pg.sprite.spritecollide(spaceship.spr, terrain.mask, False, pg.sprite.collide_mask)

while not done:
    for event in pg.event.get():
        if event.type == pg.QUIT:
            done = True

    keys = pg.key.get_pressed()
    mouse_pressed = pg.mouse.get_pressed()
    x, y = pg.mouse.get_pos()

    spaceship.check_controls()
    spaceship.update_pos()
    spaceship.update_rotation()
    if check_for_collisions() is not None:
        print('Hit! You've hit the ground with the speed:', spaceship.vely)
        exit()

    redrawGameWindow()
    clock.tick(60)

gameLoop()

Spaceship doesn't collide with the surface. I know how to fix it using simpler code, but in future I want to use randomly generated terrain. Could you help me with these collisions?

Answer 1

The mask for the Terrain is never set. Crate a proper Terrain mask:

class Terrain(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
        maskSurf = pg.Surface((display_width, display_height)).convert_alpha()
        maskSurf.fill(0)
        pg.draw.rect(maskSurf, (160, 160, 160), (self.x, self.y, display_width, 500), 0)
        self.mask = pg.mask.from_surface(maskSurf)
        print(self.mask.count())
 
        # [...]

When using pygame.mask.Mask.overlap(), then you've to check the overlapping of the Spaceship and the Terrain, rather than the Terrain and the Spaceship.
Since the Terrain mask is a mask of the entire screen, the offset for the overlap() test is the position of the Spaceship:

def check_for_collisions():
    offset = (int(spaceship.x), int(spaceship.y))
    collide = terrain.mask.overlap(spaceship.mask, offset)
    print(offset, collide)
    return collide

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Minimal example: repl.it/@Rabbid76/PyGame-SurfaceMaskIntersect

See also: Mask