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# KEA 2001-10-14
# this is the same algorithm as chaosScript1.py
# but rather than using a turtle, the script below uses the
# canvas (BitmapCanvas) and drawPointList directly
# it still draws line by line so the pattern evolves
# on the screen rather than just showing the whole thing at once
# plus the extra blit overhead for each line isn't that bad
# with a decent video card
def draw(canvas):
canvas.clear()
xOffset = 50
yOffset = 0
scale = 1.0
r = 2.9
# when r was 4.0 I got an exception when doing the int
# conversion below, so I need to consider the appropriate
# behaviour when x or y is out of bounds for an int
# and also out of bounds of the current cliprect or frame
steps = 400
inc = (4.0 - 2.9) / steps
for j in range(steps):
points = []
r += inc
x = 0.3
y = j + 30
for i in range(200):
x = r * x * (1 - x)
for i in range(300):
x = r * x * (1 - x)
x1 = int(500 * x)
x2 = int(xOffset + scale * x1)
y2 = int(yOffset + scale * y)
points.append((x2, y2))
canvas.drawPointList(points)
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