Author: Jonas Bilinkevicius

How to draw a line from the mouse cursor to a fixed point on a form 

Answer:

1   unit Unit1;
2   
3   interface
4   
5   uses
6     Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;
7   
8   type
9     TForm1 = class(TForm)
10      procedure FormCreate(Sender: TObject);
11      procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
12    private
13      { Private declarations }
14      fOldX, fOldY: Integer;
15      fLineDrawn: Boolean;
16    public
17      { Public declarations }
18    end;
19  
20  var
21    Form1: TForm1;
22  
23  implementation
24  
25  {$R *.DFM}
26  
27  procedure TForm1.FormCreate(Sender: TObject);
28  begin
29    fLineDrawn := false;
30  end;
31  
32  procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
33  
34    procedure DrawLine(Color: TColor);
35    begin
36      Canvas.Pen.Color := Color;
37      Canvas.MoveTo(fOldX, fOldY);
38      Canvas.LineTo(100, 100);
39    end;
40  
41  begin
42    if fLineDrawn then
43      DrawLine(Color);
44    fOldX := X;
45    fOldY := Y;
46    DrawLine(clRed);
47    fLineDrawn := true;
48  end;
49  
50  end.