How can I create a dynamic array of TPoints to draw a polygon?

Question:

Answer:

The easist way is to declare a type of array that has only one element, turn range checking off, access the array through the use of a variable, and call the Windows API function Polygon().

Example:

type

TPtArray = array[0..0] of TPoint;

PPtArray = ^TPtArray;

procedure DrawDynamicPolyArray(NumPoints : integer;

Canvas : TCanvas);

var

p : PPtArray;

i : integer;

begin

{$IFOPT R+}

{$DEFINE CKRANGE}

{$R-}

{$ENDIF}

GetMem(p, sizeof(TPoint) * NumPoints);

Randomize;

for i := 0 to (NumPoints -1) do begin

p^[i].x := Random(Form1.Width);

p^[i].y := Random(Form1.Height);

end;

Polygon(Canvas.Handle, p, NumPoints);

FreeMem(p, sizeof(TPoint) * NumPoints);

{$IFDEF CKRANGE}

{$UNDEF CKRANGE}

{$R+}

{$ENDIF}

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

Form1.Canvas.Brush.Color := clWhite;

Form1.Canvas.FillRect(Rect(0, 0, Form1.Width, Form1.Height));

Form1.Canvas.Brush.Color := clRed;

DrawDynamicPolyArray(SpinEdit1.Value,

Form1.Canvas);

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

SpinEdit1.MinValue := 2;

SpinEdit1.MaxValue := 1000;

SpinEdit1.Value := 100;

end;

end.