The Hpaint SOP is a viewport drawing utility for Houdini 18.5 & 19 (py2 and py3), for representing 'painted' strokes as UVed geometry. Hpaint masks your (tablet pressure sensitive) strokes to the input geometry, as well as conforming strokes to the geometry normal of underlying faces.
Download: https://github.com/aaronsmithtv/hpaint/blob/main/otls/aaron_smith__hpaint__1_2.hdalc
NOTE: I only own an Indie license, so this is currently only available as a .hdalc file. The HDA was last generated in Houdini 19.0.426 py3