unit Unit1;

{$mode objfpc}{$H+}

interface

uses  DGLOpenGL, windows, Classes, SysUtils, FileUtil, LResources, Forms, Controls,
  Graphics, Dialogs, ExtCtrls;

type

  { TForm1 }

  TForm1 = class(TForm)
    Timer1: TTimer;
    procedure FormDestroy(Sender: TObject);
    procedure FormResize(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { private declarations }
 StartTime, TimeCount, FrameCount  : Cardinal; //FrameCounter
    Frames, DrawTime                  : Cardinal; //& Timebased Movement
    procedure SetupGL;
    procedure Render;
    procedure ErrorHandler;
  public    { Public-Deklarationen }
    DC                                : HDC;  //Handle auf Zeichenfläche
    RC                                : HGLRC;//Rendering Context

    { public declarations }
  end;

var
  Form1: TForm1;

  const
      NearClipping = 1;
      FarClipping  = 1000;

implementation
uses gl, glu, glut;

procedure TForm1.FormDestroy(Sender: TObject);
begin
    DeactivateRenderingContext;
  DestroyRenderingContext(RC);
  ReleaseDC(Handle, DC);
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
   inc(FrameCount);
   Render;
   If FrameCount = 20 then
      begin
           ErrorHandler;
           FrameCount := 0;
      end;
end;

procedure TForm1.ErrorHandler;
begin
  Form1.Caption := gluErrorString(glGetError);
end;

procedure form1.render;
begin
 glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity;
  gluPerspective(45.0, ClientWidth/ClientHeight, NearClipping, FarClipping);

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity;

  glTranslatef(0, 0, -5);

  glBegin(GL_QUADS);
    glColor3f(1, 0, 0); glVertex3f(0, 0, 0);
    glColor3f(0, 1, 0); glVertex3f(1, 0, 0);
    glColor3f(0, 0, 1); glVertex3f(1, 1, 0);
    glColor3f(1, 1, 0); glVertex3f(0, 1, 0);
  glEnd;

  SwapBuffers(DC);
end;

procedure TForm1.FormResize(Sender: TObject);
  var tmpBool : Boolean;
begin
  glViewport(0, 0, ClientWidth, ClientHeight);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity;
  gluPerspective(45.0, ClientWidth/ClientHeight, NearClipping, FarClipping);

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity;
  IdleHandler(Sender, tmpBool);
end;

procedure TForm1.SetupGL;
begin
  glClearColor(0.3, 0.4, 0.7, 0.0); //Hintergrundfarbe: Hier ein leichtes Blau
  glEnable(GL_DEPTH_TEST);          //Tiefentest aktivieren
  glEnable(GL_CULL_FACE);           //Backface Culling aktivieren
end;

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  DC:= GetDC(Handle);
  if not InitOpenGL then Application.Terminate;
  RC:= CreateRenderingContext( DC,
                               [opDoubleBuffered],
                               32,
                               24,
                               0,0,0,
                               0);
  ActivateRenderingContext(DC, RC);
  SetupGL;
end;

initialization
  {$I unit1.lrs}

end.

 Application.OnIdle:= IdleHandler;