unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    DXPaintBox1: TDXPaintBox;
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
const
  ImgPath1 = 'C:\Temp\DX.jpg';
begin
  DXPaintBox1.DIB.LoadFromFile(ImgPath1);
  DXPaintBox1.Width := DXPaintBox1.DIB.Width;
  DXPaintBox1.Height := DXPaintBox1.DIB.Height;
  DXPaintBox1.Repaint;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  w,h,i: Integer;
begin
  w := DXPaintBox1.DIB.Width;
  h := DXPaintBox1.DIB.Height;

  for i := 0 to 9999 do begin
    DXPaintBox1.DIB.BlendPixel(Random(w), Random(h div 2), clRed, 255);
    DXPaintBox1.DIB.BlendPixel(Random(w), Random(h div 2) + (h div 2), clRed, 64);
  end;
  DXPaintBox1.Repaint;
end;

end.