"""

Primitives can be modified even after being "drawn" to the canvas.

This example shows how you can create interesting effects by

messing with the internals of the `canvas` object after shapes

have already been drawn to it.

"""

size(550, 300)

pen(1.5)

fill(1, 0.8)

# First, generate some rectangles all over the canvas, rotated randomly.

for i in range(3000):

grob = rect(random(WIDTH)-25, random(HEIGHT)-25,50, 50)

grob.rotate(random(360))

# Now comes the "clever" part:

# We want to sort the objects on the canvas using a custom sorting

# method; in this case, their vertical position.

# The bounds property returns the following: ( (x, y), (width, height) )

# The second arg in the call to ordered() sorts by y position

sorted_grobs = ordered(canvas, 'bounds.y')

# Now that we have all the graphic objects ("grobs") sorted,

# traverse them in order and change their properties.

t = 0.0 # a counter going from 0.0 to 1.0

d = 1.0 / len(sorted_grobs) # the delta amount added each step

for grob in sorted_grobs:

# Grobs will get bigger

grob.scale(t)

# Grobs's stroke will get darker

grob.stroke = (0.6 - t, 0.50)

t += d

# This is seriously hack-y, but you can replace the internal

# grob list of the canvas with your own to change the Z-ordering.

# Comment out this line to get a different effect:

canvas._grobs = sorted_grobs