Рисование квадрата мышкой
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Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

private
{ Private declarations }
AnchorX, AnchorY,
CurX, CurY: Integer;
Bounding: Boolean;
end;

implementation

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
AnchorX := X;
CurX := X;
AnchorY := Y;
CurY := Y;
Bounding := True;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Integer);
begin
if Bounding then
begin
Canvas.Pen.Mode := pmNot;
Canvas.Pen.Width := 2;
Canvas.Brush.Style := bsClear;
Canvas.Rectangle(AnchorX, AnchorY, CurX, CurY);
CurX := X;
CurY := Y;
Canvas.Rectangle(AnchorX, AnchorY, CurX, CurY);
end;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
if Bounding then
begin
Bounding := False;
Canvas.Pen.Mode := pmNot;
Canvas.Brush.Style := bsClear;
Canvas.Rectangle(AnchorX, AnchorY, CurX, CurY);
end;
end;