# SubtractRects — wiki

This script contains two functions that allow you to "subtract" the area of one or more rects from the area of another.
The script returns several new, smaller rects, that cover the entire area not removed by the other rect(s).

import pygame
from pygame.locals import *

def sub_rect(r1, r2):
"""remove the area of r2 from r1"""
if not r1.colliderect(r2):
return [r1]

clip = r2.clip(r1)

#first we have to see if there is a complete rect to each side of the removing rect
need_com_left = False
need_com_right = False
need_com_top = False
need_com_bottom = False

if clip.left > r1.left:
need_com_left = True
if clip.right &lt; r1.right:
need_com_right = True
if clip.top > r1.top:
need_com_top = True
if clip.bottom &lt; r1.bottom:
need_com_bottom = True

left = None
right = None
top = None
bottom = None

if need_com_left: #ok, we also need to check top and bottom here...
t = r1.top
b = r1.bottom - r1.top
l = r1.left
r = clip.left - r1.left
if need_com_top: #we need to cut a bit off the top of this
t = clip.top
if need_com_bottom:
b = clip.bottom - t

left = pygame.Rect(l, t, r, b)
if need_com_right:
t = r1.top
b = r1.bottom - r1.top
l = clip.right
r = r1.right - clip.right
if need_com_top:
t = clip.top
if need_com_bottom:
b = clip.bottom - t

right = pygame.Rect(l, t, r, b)
if need_com_top:
top = pygame.Rect(r1.left, r1.top, r1.width, clip.top-r1.top)
if need_com_bottom:
bottom = pygame.Rect(r1.left, clip.bottom, r1.width, r1.bottom-clip.bottom)

ret = []
for i in [left, right, top, bottom]:
if i: ret.append(i)

return ret

def sub_rect_list(r1, rl):
dirty = [r1]
for i in rl:
new = []
for x in dirty:
new.extend(sub_rect(x, i))
dirty = new
return dirty

#test this!
a = pygame.Rect(0,0,100,100)
b = pygame.Rect(10,10,80,80)
c = pygame.Rect(80,80,20,20)

dirty = sub_rect_list(a, [b, c])

pygame.init()
screen = pygame.display.set_mode((640, 480))

back = pygame.Surface(a.size)
back.fill((0,255,0))

screen.blit(back, (0,0))

new = pygame.Surface(a.size)
new.fill((255,0,0))

for i in dirty:
if i:
screen.blit(new, i.topleft, i)
pygame.display.flip()