Article #15919: How can I create a dynamic array of TPoints to draw a polygon?

 Question and Answer Database
FAQ919D.txt How can I create a dynamic array of TPoints to draw a polygon?
Category :Object Pascal
Platform :All
Product :All 32 bit
Question:
How can I create a dynamic array of TPoints to draw a polygon?
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.
7/16/98 4:31:28 PM

Last Modified: 01-SEP-99