This pure virtual function is called to paint the single cell at (row,col) using p, which is open when paintCell() is called and must remain open.
The coordinate system is translated so that the origin is at the top-left corner of the cell to be painted, i.e. cell coordinates. Do not scale or shear the coordinate system (or if you do, restore the transformation matrix before you return).
The painter is not clipped by default and for maximum efficiency. For safety, call setTableFlags(Tbl_clipCellPainting) to enable clipping.
Referenced by paintEvent().