How to draw a line using mouse drag?

Question

I need to draw a line in delphi using the cursor, I already have created the line code, but I can\'t get what to do next? How can do that, I push the mouse, when the line ne

Answer 1

Another technique that can be used, without the need to create a bitmap, is using the Pen.Mode property. Something like this:

  TForm2 = class(TForm)
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  private
   PO,LP: TPoint;
   draw: boolean;
  public
    { Public declarations }
  end;

procedure TForm2.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
 PO.X:= X;
 PO.Y:= Y;
 LP.X:= X;
 LP.Y:= Y;
 draw:= true;
 Canvas.Pen.Mode:= pmNotXor;
end;

procedure TForm2.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
 if draw then
  begin
   if (LP.X <> PO.X) or (LP.Y <> PO.Y) then
    begin
     Canvas.MoveTo(PO.X,PO.Y);
     Canvas.LineTo(LP.X,LP.Y);
    end;
   LP.X:= X;
   LP.Y:= Y;
   Canvas.MoveTo(PO.X,PO.Y);
   Canvas.LineTo(LP.X,LP.Y);
  end;
end;

procedure TForm2.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
 if draw then draw:= false;
end;