[Bug]: Streamplot produces unconnected lines, gaps  #24946

Bug summary

When a stream plot is drawn, curvature to the lines given by using smaller lines. However, these lines are never connected to each other. When the curvature is high the non-connection becomes visible if user saves the figure for later usage.

The visibility problem does not seem to be existent using show function. I have tested the pdf, svg, eps, png file types and all have the same issue.

Earlier commit, #25112, fixed the problem when the lines have same color and linewidth. However, when colors or linewidth vary, lines appear disconnected.

Code for reproduction

Example with color and linewidth:

#!/usr/bin/py

import numpy as np
import matplotlib.pyplot as plt

w = 3
Y, X = np.mgrid[-w:w:100j, -w:w:100j]
U = -1 - X**2 + Y
V = 1 + X - Y**2

speed = np.sqrt(U**2 + V**2)
linewidth = 1 + 5*(speed-speed.min())/np.ptp(speed)

fig = plt.figure(1)
plt.streamplot(X, Y, U, V, color=speed, linewidth=linewidth)
plt.show()
fig.savefig("streamline.pdf")

Actual outcome

Below is a screenshot of the problem. The line segments appear disconnected from each other when investigated with vector image editor such as Inkscape.

Expected outcome

A random plot produced with matplotlib. In this picture, Inkscape shows the line is connected through its nodes.

Operating system

Artix

Matplotlib Version

3.11.1

Matplotlib Backend

QtAgg

Python version

3.14.7