Smooth line joins about sprouts

[Glusk]

Update

libGDX renders lines using OpenGL.

One of the sad things about using the OpenGL rendering option in Processing is the lack of control over line weights, caps and joins.

http://www.tom-carden.co.uk/2008/02/09/new-processing-hack-line-caps-and-joins-in-opengl

Unfortunately, drawing lines is a weak point of OpenGL. The GL_LINES drawing mode is limited: it does not support line joins, line caps, non-integer line widths, widths greater than 10px, or varying widths in a single pass.

https://blog.mapbox.com/drawing-antialiased-lines-with-opengl-8766f34192dc

[Glusk]

Maybe the simple solution is still good enough:
Draw a circle centered at the common vertex with radius half the line width.