[pygame] Mask collision detection

[Petrovski <peter.blom@xxxxxxxxxxxxxxxxxxx>]

Hi,

I´m having some trouble with detecting collisions between 2 masks.

What i´m trying to do is create a sort of a terrain with a polygon,
then drop a box that should keep dropping until it hits the "terrain".

With the following code I get 2 masks that when checked with
mask.count() are greater than 0.

Problem is they are not detecting each other. I tried both
pygame.mask.from_threshold and pygame.mask.from_surface to make a mask
of the polygon. For overlapping detection I tried Mask.overlap_area
and Mask.overlap. Both did not work.

Any help would be greatly appreciated

This is my code:
+-------------------------Main class:
import pygame
import Blok
from pygame.locals import *

def main():

    pygame.init()

    screen = pygame.display.set_mode((750, 500))
    pygame.display.set_caption('Spike 2')

    #Backgrounds
    background2 = pygame.Surface(screen.get_size())
    background2 = background2.convert()
    background2.fill((0, 0, 250))

    background = pygame.Surface(screen.get_size())
    background = background.convert()
    background.fill((0, 0, 250))
    background.set_colorkey((0, 0, 250), RLEACCEL)

    #Make the terrain polygon
    area = [(0, 300), (290, 475), (450, 200), (550,475),(750,350),
(750,500),(0,500)]
    colour = (250, 0, 0)
    pygame.draw.polygon(background, colour, area)

    clock = pygame.time.Clock()
    zoneObjectSprites = pygame.sprite.RenderPlain()

    while 1:
        clock.tick(60)

        for event in pygame.event.get():
            if event.type == QUIT:
                return
            elif event.type == KEYDOWN and event.key == K_ESCAPE:
                return
            if event.type == MOUSEBUTTONDOWN:
                if event.button == 3:
                    #spawn a box at the cursor position
                    mX, mY = pygame.mouse.get_pos()
                    Blok.Blok(mX,mY).add(zoneObjectSprites)

        #Blue background and terrain
        screen.blit(background2, (0, 0))
        screen.blit(background, (0, 0))

        #Get the mask of the terrain
        #terrainmask = pygame.mask.from_threshold(background, colour,
(1, 1, 1))
        terrainmask = pygame.mask.from_surface(background)

        #print the mask count to see if its big enough
        print terrainmask.count()
        for object in zoneObjectSprites:
            object.gravity(terrainmask)
        zoneObjectSprites.draw(screen)
        pygame.display.flip()

#this calls the 'main' function when this script is executed
if __name__ == '__main__': main()


+-------------------------Blok class:
class Blok(pygame.sprite.Sprite):

    def __init__(self, X, Y):
        pygame.sprite.Sprite.__init__(self)
        self.image, self.rect = load_image('blok1.bmp',-1)
        screen = pygame.display.get_surface()
        self.area = screen.get_rect()
        self.rect.center = X, Y
        self.gravityForce = 3
        self.mask = pygame.mask.from_surface(self.image,255)
        print self.mask.count()

    def gravity(self,terrainmask):
        dy = self.mask.overlap(terrainmask,(0,0))
        print dy

        #did we hit the ground?
        if dy is not None:
            print 'hit ground'
        else:
            newpos = self.rect.move((0, self.gravityForce))
            self.rect = newpos

        #kill object if it goes offscreen
        if self.rect.top > 500:
            self.kill()