unit Unit22;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    PaintBox1: TPaintBox;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure PaintBox1Paint(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    FBitmap: TBitmap;
    procedure DrawSobel;
    procedure DrawLabels;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  // create the draw buffer bitmap
  FBitmap := TBitmap.Create;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  // free the draw buffer bitmap
  FBitmap.Free;
end;

procedure TForm1.PaintBox1Paint(Sender: TObject);
begin
  // this event is fired when the system instructs the paint box control to repaint,
  // so let's flush the prepared bitmap to the control's canvas here
  PaintBox1.Canvas.Draw(0, 0, FBitmap);
end;

procedure TForm1.DrawSobel;
var
  X, Y: Integer;
  Row: PRGBTriple;
begin
  // modify the draw buffer bitmap size and draw what is needed on it
  FBitmap.Width := Length(Img);
  FBitmap.Height := Length(Img[0]);
  for Y := 0 to FBitmap.Height - 1 do
  begin
    Row := FBitmap.ScanLine[Y];
    // ...
  end;
end;

procedure TForm1.DrawLabels;
var
  I: Integer;
begin
  // and draw some labels to that same draw buffer bitmap
  for I := 0 to High(obj_properties) do
  begin
    FBitmap.Canvas.Brush.Style := bsClear;
    FBitmap.Canvas.MoveTo(50, 50);
    FBitmap.Canvas.MoveTo(obj_properties[c].x+5, obj_properties[c].y+5);
    // ...
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  // call methods for preparing draw buffer bitmap
  DrawSobel;
  DrawLabels;
  // and tell the system we would like to repaint the paint box control
  PaintBox1.Invalidate;
end;

end.