11"""
22For the backends that supports draw_image with optional affine
33transform (e.g., agg, ps backend), the image of the output should
4- have its boundary matches the red dashed rectangle.
4+ have its boundary matches the red dashed rectangle. The extent of
5+ the image without affine transform is additionally displayed with
6+ a black solid rectangle.
57"""
68
79import numpy as np
8- import matplotlib .cm as cm
910import matplotlib .mlab as mlab
1011import matplotlib .pyplot as plt
1112import matplotlib .transforms as mtransforms
@@ -21,6 +22,25 @@ def get_image():
2122return Z
2223
2324
25+ def plot_extent (im ,rect_lw = 1.5 ,ls = "-" ,color = "Black" ,transform = None ):
26+ """Draws a rectangle denoting the extent of an image `im` altered by a
27+ transform `transform`. Additional segment markers going through then
28+ origin are also plotted.
29+
30+ `rect_lw` is the linewidth parameter used to the rectangle.
31+ """
32+ x1 ,x2 ,y1 ,y2 = im .get_extent ()
33+ ax = im .axes
34+ if transform is None :# then no specific transform will be applied
35+ transform = ax .transData
36+ # Plot the extent rectangle
37+ ax .plot ([x1 ,x2 ,x2 ,x1 ,x1 ], [y1 ,y1 ,y2 ,y2 ,y1 ],ls = ls ,lw = rect_lw ,
38+ color = color ,transform = transform )
39+ # Plot the segments parallel to the rectangle sides & going through (0, 0)
40+ ax .plot ([x1 ,x2 ], [0 ,0 ],ls = ls ,color = color ,transform = transform )
41+ ax .plot ([0 ,0 ], [y1 ,y2 ],ls = ls ,color = color ,transform = transform )
42+
43+
2444if 1 :
2545
2646fig ,ax1 = plt .subplots (1 ,1 )
@@ -29,16 +49,15 @@ def get_image():
2949origin = 'lower' ,
3050extent = [- 2 ,4 ,- 3 ,2 ],clip_on = True )
3151
32- #image rotation
52+ #Image rotation
3353trans_data2 = mtransforms .Affine2D ().rotate_deg (30 )+ ax1 .transData
3454im1 .set_transform (trans_data2 )
3555
36- # display intended extent of the image
37- x1 ,x2 ,y1 ,y2 = im1 .get_extent ()
38- x3 ,y3 = x2 ,y1
39-
40- ax1 .plot ([x1 ,x2 ,x2 ,x1 ,x1 ], [y1 ,y1 ,y2 ,y2 ,y1 ],"--r" ,lw = 3 ,
41- transform = trans_data2 )
56+ # Plot the extent of the image:
57+ # 1/ With the affine transform.
58+ plot_extent (im1 ,ls = "--" ,rect_lw = 3 ,color = "Red" ,transform = trans_data2 )
59+ # 2/ Without the affine transform (see `plot_extent` defaults).
60+ plot_extent (im1 )
4261
4362ax1 .set_xlim (- 3 ,5 )
4463ax1 .set_ylim (- 4 ,4 )