Connect stream lines if no varying width or color

Streamplot segments stream lines into small pieces of lines in order to
have different width and colors from each other. However, by doing the
segmentation the connection of lines are getting lost. The loss of
connection introduces visible gaps. This commit avoids unnecessary
segmentation of a streamline into smaller lines if there is no need to
do so. Fixing the problem only for non-varying width and color stream plots.

Author: gokberkgunes

lib/matplotlib/streamplot.py

@@ -198,8 +198,13 @@ def streamplot(axes, x, y, u, v, density=1, linewidth=None, color=None,
         tx += grid.x_origin
         ty += grid.y_origin
 
-        points = np.transpose([tx, ty]).reshape(-1, 1, 2)
-        streamlines.extend(np.hstack([points[:-1], points[1:]]))
+        # Create multiple tiny segments if varying width or color is given
+        if isinstance(linewidth, np.ndarray) or use_multicolor_lines:
+            points = np.transpose([tx, ty]).reshape(-1, 1, 2)
+            streamlines.extend(np.hstack([points[:-1], points[1:]]))
+        else:
+            points = np.transpose([tx, ty])
+            streamlines.append(points)
 
         # Add arrows halfway along each trajectory.
         s = np.cumsum(np.hypot(np.diff(tx), np.diff(ty)))