Drawing Shapes (Code)

Drawing shapes is just as easy as drawing lines. Each one takes a single statement; you just need the coordinates.

Here's a rewrite of the OnMouseUp event handler that draws shapes for all four tools:

procedure TForm1.FormMouseUp(Sender: TObject; Button TMouseButton; Shift: TShiftState;
                             X,Y: Integer);
begin
case DrawingTool of
dtLine:
begin
Canvas.MoveTo(Origin.X, Origin.Y);
Canvas.LineTo(X, Y)
end;
dtRectangle: Canvas.Rectangle(Origin.X, Origin.Y, X, Y);
dtEllipse: Canvas.Ellipse(Origin.X, Origin.Y, X, Y);
dtRoundRect: Canvas.RoundRect(Origin.X, Origin.Y, X, Y,
(Origin.X - X) div 2, (Origin.Y - Y) div 2);
end;
Drawing := False;
end;

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void __fastcall TForm1::FormMouseUp(TObject *Sender, TMouseButton Button,
                                    TShiftState Shift, int X, int Y){
  switch (DrawingTool)
  {
    case dtLine:
      Canvas->MoveTo(Origin.x, Origin.y);
      Canvas->LineTo(X, Y);
      break;
    case dtRectangle:
      Canvas->Rectangle(Origin.x, Origin.y, X, Y);
      break;
    case dtEllipse:
      Canvas->Ellipse(Origin.x, Origin.y, X, Y);
      break;
    case dtRoundRect:
      Canvas->Rectangle(Origin.x, Origin.y, X, Y, (Origin.x - X)/2,
                        (Origin.y - Y)/2);
      break;
  }
  Drawing = false;
}

Of course, you also need to update the OnMouseMove handler to draw shapes:

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procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
if Drawing then
begin
Canvas.Pen.Mode := pmNotXor;
case DrawingTool of
dtLine: begin
Canvas.MoveTo(Origin.X, Origin.Y);
Canvas.LineTo(MovePt.X, MovePt.Y);
Canvas.MoveTo(Origin.X, Origin.Y);
Canvas.LineTo(X, Y);
end;
dtRectangle: begin
Canvas.Rectangle(Origin.X, Origin.Y, MovePt.X, MovePt.Y);
Canvas.Rectangle(Origin.X, Origin.Y, X, Y);
end;
dtEllipse: begin
Canvas.Ellipse(Origin.X, Origin.Y, X, Y);
Canvas.Ellipse(Origin.X, Origin.Y, X, Y);
end;
dtRoundRect: begin
Canvas.RoundRect(Origin.X, Origin.Y, X, Y,
(Origin.X - X) div 2, (Origin.Y - Y) div 2);
Canvas.RoundRect(Origin.X, Origin.Y, X, Y,
(Origin.X - X) div 2, (Origin.Y - Y) div 2);
end;
end;
MovePt := Point(X, Y);
end;
Canvas.Pen.Mode := pmCopy;
end;

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void __fastcall TForm1::FormMouseMove(TObject *Sender, TMouseButton Button,
  TShiftState Shift, int X, int Y)
{
  if (Drawing)
  {
    Canvas->Pen->Mode = pmNotXor;        // use XOR mode to draw/erase
    switch (DrawingTool)
    {
      case dtLine:
        Canvas->MoveTo(Origin.x, Origin.y);
        Canvas->LineTo(MovePt.x, MovePt.y);
        Canvas->MoveTo(Origin.x, Origin.y);
        Canvas->LineTo(X, Y);
        break;
      case dtRectangle:
        Canvas->Rectangle(Origin.x, Origin.y, MovePt.x, MovePt.y);
        Canvas->Rectangle(Origin.x, Origin.y, X, Y);
        break;
      case dtEllipse:
        Canvas->Ellipse(Origin.x, Origin.y, MovePt.x, MovePt.y);
        Canvas->Ellipse(Origin.x, Origin.y, X, Y);
        break;
      case dtRoundRect:
        Canvas->Rectangle(Origin.x, Origin.y, MovePt.x, MovePt.y,
                         (Origin.x - MovePt.x)/2,(Origin.y - MovePt.y)/2);
        Canvas->Rectangle(Origin.x, Origin.y, X, Y,
                         (Origin.x - X)/2, (Origin.y - Y)/2);
        break;
    }
    MovePt = Point(X, Y);
  }
  Canvas->Pen->Mode = pmCopy;
}

Typically, all the repetitious code that is in the above example would be in a separate routine. The next topic shows all the shape-drawing code in a single routine that all mouse-event handlers can call.