Hi,

I am expanding lines using the geometry shader to make them "thick." I do the expansion in projective NDC space in 2D. My first approach was to just expand in the direction of the line normal in 2D. However, this creates discontinuities where line segments meet in a line strip (see left side of http://postimg.org/image/f5frxyp1v/). My 2nd approach was to use line strip with adjacency, and access the adjacent lines to do a sort of normal averaging. This works well if the lines do not take "sharp turns", however, there are cases where the averaged normal isn't a good choice and it creates a thin quad (see right side of http://postimg.org/image/f5frxyp1v/).

Does anyone know a good strategy for handling the "sharp" line turns?

I implemented a 3D based technique a couple months ago based on some discussions I saw online that seems at least similar to your need. The idea is that when you expand the line in the geometry shader that you ensure the end of the line is extruded forward by the same amount as the thickness of the expanded line. When you do this, you also include the original vertex location in the expanded vertex layout.

Finally in the pixel shader you test to see how far from the end point you are. If you can determine that your pixel is from the end point area, then you can test to see how far from the end point it is, and kill the pixel if you are too far away from it. That essentially creates a sphere just like TheUnnamable mentioned at each end point.

I'm sure you can reproduce the same thing in 2D without too much trouble. It is certainly a bit heavier algorithm than what you are currently doing, but the results look nice and it would solve your current issue. Another possible solution with some sample code can be found here. I hope that helps!