glClearColor raised exception TOpenGLComponent Lazarus - opengl

Question

I use Lazarus (under Linux) Please anybody help me. I have problem. I have install LasOpenGLContext. There is "OpenGL Controll" at components panel. And I wish to draw a simple cube. But I can not do it. I get raised an exception class 'External:SIGSEGV' What's wrong? Please, if any ideas.
unit Ex1;
{$mode objfpc}{$H+}
{$LinkLib GL}
interface
uses
Classes, SysUtils, FileUtil, OpenGLContext, Forms, Controls, Graphics, gl, glu, Glut,
Dialogs, ExtCtrls, LazOpenGLContext, LCLType;
type
{ Tfrm }
Tfrm = class(TForm)
OpenGLControl1: TOpenGLControl;
Timer: TTimer;
procedure FormCreate(Sender: TObject);
procedure TimerTimer(Sender: TObject);
private
{ private declarations }
public
cube_rotation: GLFloat;
Speed: Double;
{ public declarations }
end;
var
frm: Tfrm;
implementation
{$R *.lfm}
{ Tfrm }
procedure Tfrm.FormCreate(Sender: TObject);
begin
glClearColor(1.0, 1.0, 1.0, 1.0); // here brakepoint raised an exception class 'External:SIGSEGV'
glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, double(width) / height, 0.1, 100.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0, 0.0,-6.0);
glRotatef(cube_rotation, 1.0, 1.0, 1.0);
glBegin(GL_QUADS);
glColor3f(0.0,1.0,0.0);
glVertex3f( 1.0, 1.0,-1.0);
glVertex3f(-1.0, 1.0,-1.0);
glVertex3f(-1.0, 1.0, 1.0);
glVertex3f( 1.0, 1.0, 1.0);
glEnd();
glBegin(GL_QUADS);
glColor3f(1.0,0.5,0.0);
glVertex3f( 1.0,-1.0, 1.0);
glVertex3f(-1.0,-1.0, 1.0);
glVertex3f(-1.0,-1.0,-1.0);
glVertex3f( 1.0,-1.0,-1.0);
glEnd();
glBegin(GL_QUADS);
glColor3f(1.0,0.0,0.0);
glVertex3f( 1.0, 1.0, 1.0);
glVertex3f(-1.0, 1.0, 1.0);
glVertex3f(-1.0,-1.0, 1.0);
glVertex3f( 1.0,-1.0, 1.0);
glEnd();
glBegin(GL_QUADS);
glColor3f(1.0,1.0,0.0);
glVertex3f( 1.0,-1.0,-1.0);
glVertex3f(-1.0,-1.0,-1.0);
glVertex3f(-1.0, 1.0,-1.0);
glVertex3f( 1.0, 1.0,-1.0);
glEnd();
glBegin(GL_QUADS);
glColor3f(0.0,0.0,1.0);
glVertex3f(-1.0, 1.0, 1.0);
glVertex3f(-1.0, 1.0,-1.0);
glVertex3f(-1.0,-1.0,-1.0);
glVertex3f(-1.0,-1.0, 1.0);
glEnd();
glBegin(GL_QUADS);
glColor3f(1.0,0.0,1.0);
glVertex3f( 1.0, 1.0,-1.0);
glVertex3f( 1.0, 1.0, 1.0);
glVertex3f( 1.0,-1.0, 1.0);
glVertex3f( 1.0,-1.0,-1.0);
glEnd();
cube_rotation += 5.15 * Speed;
OpenGLControl1.SwapBuffers;
end;
procedure Tfrm.TimerTimer(Sender: TObject);
begin
end;
end.

Answer 1

You seem to be missing the OpenGL context creation. Without it every OpenGL call can crash your program. I haven't used Lazarus, but according to their website the code to create a context could be the following:
procedure TForm1.FormCreate(Sender: TObject);
begin
GLbox:= TOpenGLControl.Create(Form1);
GLbox.AutoResizeViewport:= true;
GLBox.Parent := self;
GLBox.MultiSampling:= 4;
GLBox.Align := alClient;
GLBox.OnPaint := #GLboxPaint; //for "mode delphi" this would be "GLBox.OnPaint := GLboxPaint"
GLBox.invalidate;
end;