How can I draw transparent lines where the color becomes stronger when they overlap?
When you draw a bunch of transparent lines in matplotlib like this, you get a nice effect; when they overlap they are a bit darker.
from pylab import * for _ in xrange(1000) : plot(np.random.randn(2),np.random.randn(2),alpha=0.1,color='k') show()
It looks like this:
But if you draw one long line like this that overlaps with itself like this, the line doesn't "interact with itself." It looks like this:
I would like to draw a single curve that overlaps with itself, so that the more it overlaps with itself, the darker it becomes. If I use a loop to break up the curve and draw each line segment separately, I get what I want, but I also get ugly and unacceptable artifacts where the line segments meet, making the curve looked like a dotted or dashed line.. Like this:
Is there any nice way to draw a curve so that it becomes darker when it overlaps with itself, but you don't get artifacts like those just described?
When using a loop to break up the curve and draw each line segment separately, you can try to use the
solid_capstyle argument to
plot. The default is
"projecting", but you could try using
"butt" and see if it helps.
plt.plot(x,y, alpha=0.1, c="k", solid_capstyle="butt")
This might reduce the effect a little.
import matplotlib.pyplot as plt import numpy as np def squiggle_xy(a, b, c, d, i=np.arange(0.0, 2*np.pi, 0.05)): return np.sin(i*a)*np.cos(i*b), np.sin(i*c)*np.cos(i*d) x,y = squiggle_xy(2.5, 2, 1, 3) fig, ax = plt.subplots(ncols=2, figsize=(6,3)) ax.set_title("solid_capstyle=\"projecting\"") ax.set_title("solid_capstyle=\"butt\"") for i in range(len(x)-1): print x[i:i+2] ax.plot(x[i:i+2], y[i:i+2], alpha=0.1, lw=10, solid_capstyle="projecting", c="b") ax.plot(x[i:i+2], y[i:i+2], alpha=0.1, lw=10, solid_capstyle="butt", c="b") plt.show()
See this question for a good explanation of