You can achieve the same effect as MoveTo by setting the Canvas's PenPos... for example, "Canvas.PenPos.x := 20;", "Canvas.PenPos.y := 50", or "Canvas.PenPos := Point(20,50);".

The Canvas uses the current pen position when drawing lines. The pen position defaults to (0,0), which is the screen top-left (remember?). So, for example, after the call "Canvas.LineTo(100,100);" there would be a line from (0,0) to (100, 100). The next line starts from the last co-ordinates, so if the next call was "Canvas.LineTo(200, 100);" another line would be drawn from (100, 100) to (200, 100). This is why the MoveTo method is useful - you usually don't want connected lines.

Lines drawn with LineTo use the current Canvas pen (of type TPen). This is meant to be a metaphor for your common real-world pen, and is used for line drawing and outlining shapes. You can change the Canvas pen to change the line drawn. The most common use is changing the width of the pen - "Canvas.Pen.Width := 4";, which will give different sized lines (in this case, larger ones). Another useful pen property is its Color (yuck, American spelling) - "Canvas.Pen.Color := clLime;".

Let's get busy then:

procedure TForm1.FormCreate(Sender: TObject);
begin
  // initialise the random
  // number generator
  Randomize;
end;

const NUM_LINES = 2000;

procedure TForm1.DrawLines;
var
  i: Integer;
begin
  for i := 0 to NUM_LINES - 1 do
  begin
    Canvas.Pen.Color :=
         RGB(Random(256),
             Random(256),
             Random(256)
             );
    Canvas.LineTo
       (Random(ClientWidth),
        Random(ClientHeight));
  end;
end;

Call the DrawLines procedure in a button's OnClick handler. The code simply draws 2000 lines to random locations, each time using a random colour. The function RGB, by the way, takes values for the red, green and blue components of a color (from 0 to 255) and gives you back a TColor. I'll talk about colors later. Here's the screen:

   My Lines Are Missing!
Now, after the lines are drawn, move your form off the screen a bit and back on. You'll notice that the sections moved off the screen have had their lines erased! This is not a bug, and can be resolved quite easily. However, not yet ;-). First, I want to show you some more drawing - this time shapes.

   Question, Suggestions...
If you have any questions or comments to this (huge) article, please post them on the Delphi Programming Forum. Discuss!