Question

I’m developing a game (a missile command clone) where I need to check if a surface (a building) collides with a point (a missile).

How can I check if a missile hits a building?

A Rect has the collidepoint method, but I want it to be pixel perfect.

=> using a Rect => => but it should be pixel perfect =>

Answer 1

You can use a Mask and use it’s get_at method.

Returns nonzero if the bit at (x,y) is set.

Creating a mask is quite simple by calling pygame.mask.from_surface

Returns a Mask from the given surface.
Makes the transparent parts of the Surface not set, and the opaque parts set.

---

So, given the following helper method for some vector math:

def sub(u, v):
  return [ u[i]-v[i] for i in range(len(u)) ]

use the following code to check if a given point is inside a mask/surface:

# create mask from surface
mask = pygame.mask.from_surface(building.surface)

# translate the position of the missile,
# since the top left coordinate of the mask is always (0, 0)
rel_point = sub(missile.position, building.position)
try: 
    if mask.get_at(rel_point): 
        # point in mask
        do_something()
except IndexError: 
    pass