Needed a bit of twisting in generic private func behind the imm_draw_circle helpers, but think it's fine. Note that this demonstrate yet another downside of new dashed shader compared to olde line style: not only does it needs more complex setup, and can only work with PRIM_LINES type of primitives, but it also behaves totally wrong with chained short segments! We really need to find a better way to do this effect at some point. :(