Right now, in Krita, the "cusp/corner" nodes(that is nodes that can be sharp corners, are shown as circles in the edit-shapes tool. Conversely, the "symmetric" nodes, that is, nodes where the control points are on one lines and are the same distance from the node, are diamonds. This feels a bit odd and intuitive. I would expect round nodes to be smooth and blocky nodes to be an indicator of corners. Inkscape uses diamonds for corners too.
Git commit f76188169f20ab879929a0b44a10139858f7e8da by Dmitry Kazakov. Committed on 13/02/2018 at 12:52. Pushed by dkazakov into branch 'kazakov/tool-handles-refactoring'. Fix path editing handles to be consistent with Inkscape M +3 -3 libs/flake/KoPathPoint.cpp https://commits.kde.org/krita/f76188169f20ab879929a0b44a10139858f7e8da
Git commit b8111eeebe004a9c094bc8cd3d526d59946cf749 by Dmitry Kazakov. Committed on 19/02/2018 at 19:56. Pushed by dkazakov into branch 'master'. Fix path editing handles to be consistent with Inkscape M +3 -3 libs/flake/KoPathPoint.cpp https://commits.kde.org/krita/b8111eeebe004a9c094bc8cd3d526d59946cf749