intersect

def intersect( x1, y1, x2, y2, x3, y3, x4, y4 ):
	"""Calculates the intersection of line P1-P2 with P3-P4."""
	slope12 = ( float(y2) - float(y1) ) / ( float(x2) - float(x1) )
	slope34 = ( float(y4) - float(y3) ) / ( float(x4) - float(x3) )
	
	x = ( slope12 * x1 - y1 - slope34 * x3 + y3 ) / ( slope12 - slope34 )
	y = slope12 * ( x - x1 ) + y1
	
	return x, y
	

# this also tests for vertical slopes:

def intersectionWithNSPoints( pointA, pointB, pointC, pointD ):
	"""
	Returns an NSPoint of the intersection AB with CD.
	Or False if there is no intersection
	"""
	try:
		x1, y1 = pointA.x, pointA.y
		x2, y2 = pointB.x, pointB.y
		x3, y3 = pointC.x, pointC.y
		x4, y4 = pointD.x, pointD.y
		
		try:
			slope12 = ( float(y2) - float(y1) ) / ( float(x2) - float(x1) )
		except:
			slope12 = None # vertical
			
		try:
			slope34 = ( float(y4) - float(y3) ) / ( float(x4) - float(x3) )
		except:
			slope34 = None # vertical
		
		if slope12 == slope34:
			# parallel, no intersection
			return False
		elif slope12 is None:
			# first line is vertical
			x = x1
			y = slope34 * ( x - x3 ) + y3
		elif slope34 is None:
			# second line is vertical
			x = x3
			y = slope12 * ( x - x1 ) + y1
		else:
			# both lines have an angle
			x = ( slope12 * x1 - y1 - slope34 * x3 + y3 ) / ( slope12 - slope34 )
			y = slope12 * ( x - x1 ) + y1

		return NSPoint( x, y )
		
	except Exception as e:
		print str(e)
		return False

slope12 == slope34, wenn sie parallel sind, also bei den Divisionen oben dasselbe rauskommt. Das kann ein Zahlenwert sein oder zweimal False.

ja, klar. der witz ist nur, dass ich ja nicht den schnittpunkt zweier gerade gesucht hab, sondern zweier strecken. hab das dann aber einfach hinterher noch abgefragt, das ging dann.