Painting by projecting every pixel of the brush against the 3d model
Painting by projecting the center of the brush against the 3d model and then applying the stroke to that location on the 2D map
UV Mapping is done by allocating the polygon next to adjacent already allocated polygons when the user finally paints there.
Multi-resolution is done by making the size of new polygons based on the amount of screen space they took up for painting. So zooming in to paint implies a need for bigger/more texels.
Texture islands are packed by treating them as rectangles via bounding box and proceeding to do 2D bin packing.