Smooth line joins

[Glusk]

libGDX provides no line joining utilities/settings.

http://www.bluevoid.com/opengl/sig00/advanced00/notes/node290.html

The following SO answer shows how to compute Milter join points (in general terms, although the question was about libGDX in specific).

An easy round join solution:

Draw a circle centered at the common vertex with radius half the line width. Sounds easy but if not drawn carefully, there would be serious overdraw.

http://artgrammer.blogspot.com/search/label/opengl

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If drawing a curve, a texture can be applied to triangle strips. Example:

https://badlogicgames.com/forum/viewtopic.php?f=11&t=18940 (The forum was shut down).

[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.