Adding a checkbox in a grid whose OnDrawColumnCell handler is generic

Following on from this question and its very useful answer: I implemented a variation of Ken's answer in my big project where I had similar code appearing in many forms. But I noticed that I also had some forms with DrawColumnCell handlers as follows

procedure TEditDocket.DBGrid1DrawColumnCell(Sender: TObject;
           const Rect: TRect; DataCol: Integer; Column: TColumn;
           State: TGridDrawState);
var
 DrawRect: TRect;

begin
 if column.Index  = 3 then
  begin
   DrawRect:= Rect;
   drawrect.left:= rect.left + 24;
   InflateRect (DrawRect, -1, -1);
   dbgrid1.Canvas.FillRect (Rect);
   DrawFrameControl (dbgrid1.Canvas.Handle, DrawRect, DFC_BUTTON,
                 ISChecked[Column.Field.AsInteger]);
  end
 else dbgrid1.DefaultDrawColumnCell (Rect, DataCol, Column, State);
end;

How I could combine the above code with a general OnDrawColumnCell handler? Is it possible to define the general handler with an extra parameter (which would be the column index; if it were -1 then the above code would not execute)? How would I pass such a parameter to the handler?

Solution

Independently, I reached the following answer using the 'tag' property of the grid.

In the client form, I write

 dbGrid1.OnDrawColumnCell:= dm.DBGrid1DrawColumnCell;
 dbGrid1.tag:= 3;  // column with checkbox
 dbGrid2.OnDrawColumnCell:= dm.DBGrid1DrawColumnCell;
 dbGrid2.tag:= $23;  // both columns 2 and 3 are checkboxes

The default handler is now

procedure TDm.DBGrid1DrawColumnCell(Sender: TObject; const Rect: TRect;
          DataCol: Integer; Column: TColumn; State: TGridDrawState);
const
  IsChecked : array[0..1] of Integer =
                (DFCS_BUTTONCHECK, DFCS_BUTTONCHECK or DFCS_CHECKED);

var
 DrawRect: TRect;
 tag: integer;
 cols: set of byte;

begin
 if sender is TDBGrid then
  begin
   tag:= TDBGrid (sender).tag;
   if (THackDBGrid (sender).DataLink.ActiveRecord + 1 = THackDBGrid (sender).Row)
   or (gdFocused in State) or (gdSelected in State) then
    with TDBGrid (sender) do
     begin
      canvas.Brush.Color:= clMoneyGreen;
      canvas.font.color:= clNavy;
     end;

   cols:= [];
   while tag > 0 do
    begin
     cols:= cols + [tag mod 16];
     tag:= tag div 16
    end;

   if column.Index in cols then
    begin
     DrawRect:= Rect;
     drawrect.left:= rect.left + 24;
     InflateRect (DrawRect, -1, -1);
     TDBGrid (sender).Canvas.FillRect (Rect);
     DrawFrameControl (TDBGrid (sender).Canvas.Handle, DrawRect, DFC_BUTTON,
                   ISChecked[Column.Field.AsInteger]);
    end
   else
    begin
     TDBGrid (sender).DefaultDrawColumnCell (Rect, DataCol, Column, State);
    end;
  end;
end;

This means that column 0 must never be a checkbox. Using a set allows up to four columns in the grid to be checkboxes.