The only difference from 2.7x is that we were using glLineWidth(2.0) before,
which is not supported reliably in the latest OpenGL.
Big thanks to Clément Foucault for helping with this, on the design as well as
debugging the implementation.
For the records, I'm creating and destroying batches for the path geometry at
every draw. The pipeline is as follows:
1. Create GPUBatch with all the points
2. Create new shgroup with simple shader
3. Add call with the gpubatch
4. Save it in a linked list in stl->g_data
5. Free it after all drawing is done
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