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OpenGL: Basic methods of drawing

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Michal Bugala

Post subject: OpenGL: Basic methods of drawing

Posted: 14 Feb 2010, o 13:01

Joined: 29 Dec 2009, o 11:44
Posts: 20

Especially for the needs of this tutorial I have prepared a very simple framework which consists of the following modules:
* GameDevice (contains processes essential to initialize OpenGL)
* GameTimer (clock defining time of displaying successive frames of animation)
* GameEngine (object linking all modules of framework)
Connecting OpenGL to your application is not difficult today – it is enough to look at the following code:

Code:

unit Unit1;

interface

uses Classes, Controls, Forms;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    procedure RENDER(Sender: TObject);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

uses OpenGL, GamecaskEngine;

var Engine: TGamecaskEngine;

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  Engine:= TGamecaskEngine.Create();
  Engine.Control:= TCustomControl(Form1);
  Engine.GameInitialize();
  Engine.GameDevice.Align:= alClient;
  Engine.GameDevice.Size:= Point(200, 200);
  Engine.GameDevice.OnRender:= RENDER;
  Engine.GameTimer.Interval:= 100;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Engine.GameFinalize();
  Engine.Free();
end;

procedure TForm1.RENDER(Sender: TObject);
begin
  //
end;

end.

As the title of tutorial suggests we deal with essentials of OpenGL and not writing frameworks, that is why let’s concentrate only on RENDER procedure. The RENDER procedure is a place where we will draw subsequent frames of animation with refreshing every X milisecond. X value is a number of miliseconds after which another "painting" of the animation frame takes place, and we attribute it to a variable Interval of a clock:

Code:

Engine.GameTimer.Interval:= 100; 
// 1000 miliseconds equals 1 second so in a second 
// RENDER procedure will be evoked 10 times. 

Below there is an attachment with the full source code of the application.

Attachment:

File comment: Source code.

example0.zip [7.42 KiB]
Downloaded 57 times

Now we can deal with basic methods of drawing in OpenGL.

Code:

procedure TForm1.RENDER(Sender: TObject);
begin

  glColor3f(1, 0, 0);   // color RGB: red, green, blue
  glBegin(GL_POINTS);
    glVertex3f(0, 0, 0);   // x, y, z
  glEnd;

  glColor3f(0, 1, 0);
  glBegin(GL_LINES);
    glVertex3f(-80, 10, 0);
    glVertex3f( 80, 10, 0);
  glEnd;

  glColor3f(0, 0, 1);
  glBegin(GL_TRIANGLES);
    glVertex3f( 0, 40, 0);
    glVertex3f(40, 60, 0);
    glVertex3f(20, 20, 0);
  glEnd;

  glColor3f(1, 1, 0);
  glBegin(GL_QUADS);
    glVertex3f(-40, -40, 0);
    glVertex3f(-60, -40, 0);
    glVertex3f(-60, -60, 0);
    glVertex3f(-40, -60, 0);
  glEnd;

  glColor3f(0, 1, 1);
  glBegin(GL_POLYGON);
    glVertex3f(40, -40, 0);
    glVertex3f(60, -40, 0);
    glVertex3f(60, -60, 0);
    glVertex3f(40, -70, 0);
    glVertex3f(20, -30, 0);
    glVertex3f(40, -10, 0);
  glEnd;

end;

Result of the above code can be visible in the following picture.

Below there is a source code of a program which describes the way of creating animation with the possibility of connecting OpenGL window to a component of TPanel type.

Attachment:

File comment: Source code.

example1.zip [7.82 KiB]
Downloaded 55 times

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