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#
# 20,000 Light Years Into Space
# This game is licensed under GPL v2, and copyright (C) Jack Whitham 2006-07.
#
# Line drawing algorithm. Produces a list. This is useful for all sorts
# of linear interpolations.
#
# Page 78, Computer Graphics Principles and Practice (2nd. Ed), Foley et al.
def Line((x1,y1),(x2,y2)):
x1 = int(x1)
y1 = int(y1)
x2 = int(x2)
y2 = int(y2)
dx = x2 - x1
dy = y2 - y1
if ( abs(dx) < abs(dy) ):
# Gradient is steeper than 1. Correct this.
return [ (x,y) for (y,x) in Line((y1,x1),(y2,x2)) ]
if ( dx < 0 ):
# Line is reversed. Correct this.
l = Line((x2,y2),(x1,y1))
l.reverse()
return l
if ( dy < 0 ):
direction = -1
dy = - dy
else:
direction = 1
d = ( 2 * dy ) - dx
incr_e = 2 * dy
incr_ne = 2 * ( dy - dx )
y = y1
l = [(x1,y)]
for x in range(x1, x2 + 1):
if ( d <= 0 ):
d += incr_e # move east
else:
d += incr_ne # move northeast
y += direction
l.append((x,y))
if ( y != y2 ):
l.append((x2,y2))
return l
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