Hi! This is my first post here! I started OpenGL one week ago and I like it so far. Now I am working on a little application that rotates a rectangle. I already added a texture. But now I got some Problems with my light. I'm trying to make a light like the sun. It should be constant. Here is my source code so far:

// Textures by CGTextures
#include <SDL/SDL.h>
#include <GL/glu.h>
#include <GL/gl.h>
#include <string>
#include <iostream>
using namespace std;

// Funktion zum Zeichnen
void DrawScreen();
GLuint LoadTexture(string name);

GLuint Texture[2];

int main(int argc, char* argv[]) {

const SDL_VideoInfo* info = NULL; // Zum lesen von Video Informationen
SDL_Surface *Surf_Window; // Surface des windows
SDL_Event event; // Für das event handling
int bpp; // bit per pixer -> Bildschirmtiefe
int width = 800, height = 600; // Breite und Höhe des Fensters
bool active = true; // Die Loop läuft solange, bis diese Variable false ist

// SDL Initialisieren
if ( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
 return -1;
}

// Setze bit per pixel
info = SDL_GetVideoInfo();
bpp = info->vfmt->BitsPerPixel;

// Setze OpenGL Attribute
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5); // größe des roten Framebuffers
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5); // größe des grünen Framebuffers
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5); // größe des blauen Framebuffers
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16); // Größe des Tiefenpuffers
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1); // Doppel Pufferung einschalten

// Setze SDL in den Video Mode
if((Surf_Window = SDL_SetVideoMode(width, height, bpp, SDL_OPENGL)) == NULL) {
    return -1;
}

glEnable(GL_TEXTURE_2D); // Erlaubt die Benutzung von 2D Texturen
glShadeModel(GL_SMOOTH); // Farbtechnik auf SMOOTH setzen
                         // Bildet Farbverläufe zwischen Eckpunkten
glClearColor(0.3, 0.3, 0.7, 1.0); // Farbe mit der der
                                  // Bildschirm bereinigt wird
glViewport(0, 0, width, height); // Gibt OpenGL den "Malbereich"
glMatrixMode(GL_PROJECTION); // Matrix Mode ändern
glLoadIdentity(); // Setzt die aktieve Matrix zurück
gluPerspective(60.0, width/height, 1.0, 1024.0); // Ändert die Perspektive
glMatrixMode(GL_MODELVIEW); // Ändert den Matrix Mode wieder auf MODELVIEW

// Depth Puffer Einstellen
glClearDepth(1.0f); // Wert festlegen mit dem der
                    // Tiefenpuffer beim Löschen gefüllt wird
glEnable(GL_DEPTH_TEST); // Tiefen Test aktivieren
glDepthFunc(GL_LEQUAL); // Legt fest wann ein Segment den Test besteht

glEnable(GL_LIGHTING); // Erlaubt das Benutzen von Lichtquellen
glEnable(GL_COLOR_MATERIAL);
glEnable(GL_LIGHT0);

// Eigenschaften der Lichtquellen
GLfloat LightAmbient[]= {0.0f, 0.0f, 0.0f, 1.0f};
GLfloat LightDiffuse[]= {1.0f, 1.0f, 1.0f, 1.0f};
GLfloat LightSpecular[]= {1.0f, 1.0, 1.0f, 1.0f};
glLightfv(GL_LIGHT0, GL_AMBIENT, LightAmbient);
glLightfv(GL_LIGHT0, GL_DIFFUSE, LightDiffuse);
glLightfv(GL_LIGHT0, GL_SPECULAR, LightSpecular);
glColorMaterial(GL_FRONT_AND_BACK, GL_AMBIENT);
glColorMaterial(GL_FRONT_AND_BACK, GL_DIFFUSE);

/*
// Culling
glCullFace(GL_BACK); // Hinterseite soll nicht angezeigt werden
glFrontFace(GL_CCW); // definiere die Vorderseite
glEnable(GL_CULL_FACE); // Culling aktivieren
*/

// Textur laden
Texture[0] = LoadTexture("images/texture1.bmp");
Texture[1] = LoadTexture("images/texture2.bmp");

// Loop startet
while(active) {

 // bearbeite Events
 while(SDL_PollEvent(&event)) {
  switch(event.type) {
   case SDL_KEYDOWN:
    switch(event.key.keysym.sym) {
     case SDLK_ESCAPE:
      active = false;
      break;
     case SDLK_SPACE:
      SDL_WM_ToggleFullScreen(Surf_Window);
      break;
    }
    break;
   case SDL_QUIT:
    active = false;
    break;
  }
 }

 // Bildschirm zeichnen
 DrawScreen();

 // Warten, um den CPU nicht auf 100% zu bringen
 SDL_Delay(50);

}

// Textur löschen
glDeleteTextures(sizeof(Texture) / sizeof(GLuint), Texture);

// SDL beenden
SDL_Quit();

return 0;
}

void DrawScreen() {

// Variable die den aktuellen Winkel speichert
static float angle = 0.0f;
static GLfloat LightPosition[]= {-2.0f, 1.0, 1.0f, 1.0f};

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Buffer leeren
glLoadIdentity(); // Matrix zurücksetzen

gluLookAt(0, 0, -10, 0, 0, 0, 0, 1, 0);
glLightfv(GL_LIGHT0, GL_POSITION, LightPosition);

glDisable(GL_LIGHT0);
glTranslatef( 0.0f, -1.0f,-5.0f); // verschiebt die Matrix
glRotatef(angle, 0.0f, 1.0f, 0.0f); // rotiert die Matrix um die y Achse
glEnable(GL_LIGHT0);
angle += 2; // Winkel vergrößern -> drehen
if(angle >= 360) // Wenn der Winkel größer gleich 360 wird auf 0 setzten
 angle = 0;      // da 0° = 360°
glBindTexture(GL_TEXTURE_2D, Texture[0]);

glBegin(GL_QUADS); // Zeichnen eines Viereckes

 // Boden
 glTexCoord2i(0, 1);
 glVertex3f(-1.0f, 0.0, 1.0);
 glTexCoord2i(0, 0);
 glVertex3f(-1.0f, 0.0,-1.0);
 glTexCoord2i(1, 0);
 glVertex3f( 1.0f, 0.0,-1.0);
 glTexCoord2i(1, 1);
 glVertex3f( 1.0f, 0.0, 1.0);

 // Oben
 glTexCoord2i(0, 1);
 glVertex3f(-1.0f, 2.0, 1.0);
 glTexCoord2i(0, 0);
 glVertex3f(-1.0f, 2.0,-1.0);
 glTexCoord2i(1, 0);
 glVertex3f( 1.0f, 2.0,-1.0);
 glTexCoord2i(1, 1);
 glVertex3f( 1.0f, 2.0, 1.0);

 // Links
 glTexCoord2i(1, 1);
 glVertex3f(-1.0f, 0.0, 1.0);
 glTexCoord2i(1, 0);
 glVertex3f(-1.0f, 2.0, 1.0);
 glTexCoord2i(0, 0);
 glVertex3f(-1.0f, 2.0,-1.0);
 glTexCoord2i(0, 1);
 glVertex3f(-1.0f, 0.0,-1.0);

 // Rechts
 glTexCoord2i(1, 1);
 glVertex3f( 1.0f, 0.0, 1.0);
 glTexCoord2i(1, 0);
 glVertex3f( 1.0f, 2.0, 1.0);
 glTexCoord2i(0, 0);
 glVertex3f( 1.0f, 2.0,-1.0);
 glTexCoord2i(0, 1);
 glVertex3f( 1.0f, 0.0,-1.0);

 // Vorne
 glTexCoord2i(1, 1);
 glVertex3f(-1.0f, 0.0, 1.0);
 glTexCoord2i(0, 1);
 glVertex3f( 1.0f, 0.0, 1.0);
 glTexCoord2i(0, 0);
 glVertex3f( 1.0f, 2.0, 1.0);
 glTexCoord2i(1, 0);
 glVertex3f(-1.0f, 2.0, 1.0);

 // Hinten
 glTexCoord2i(1, 1);
 glVertex3f(-1.0f, 0.0,-1.0);
 glTexCoord2i(0, 1);
 glVertex3f( 1.0f, 0.0,-1.0);
 glTexCoord2i(0, 0);
 glVertex3f( 1.0f, 2.0,-1.0);
 glTexCoord2i(1, 0);
 glVertex3f(-1.0f, 2.0,-1.0);

glEnd(); // Zeichnen beenden

SDL_GL_SwapBuffers(); // erneuert den Bildschirm

}

GLuint LoadTexture(string name) {

GLuint texture; // Rückgabewert, der die id der Textur enthält
SDL_Surface *surface; // SDL Surface zum laden der Bit Map
GLenum textureFormat; // Variable zum Speichern der Formates
GLint colors; // Variable zum Speichern von der Anzahl der Farben
              // RGB  -> 3
              // RGBA -> 4

// Öffnen der Bitmap und Speichern in dem Surface
if((surface = SDL_LoadBMP(name.c_str())) == NULL) {
 cout << "Couldn't find texture" << endl;
}

// speichere Anzahl der bytes
colors = surface->format->BytesPerPixel;

// Definition des Formates
if(colors == 4) {
  if(surface->format->Rmask == 0x000000ff)
    textureFormat = GL_RGBA;
  else
    textureFormat = GL_BGRA;
} else if(colors == 3) {
  if (surface->format->Rmask == 0x000000ff)
    textureFormat = GL_RGB;
  else
    textureFormat = GL_BGR;
} else {
    cout << "Can not use color format of the bit map" << endl;
}

glGenTextures(1, &texture); // Namen(Nummer) der Textur zuweisen
glBindTexture(GL_TEXTURE_2D, texture); // an die 2D Textur binden
// Setzen der Textureigenschaften
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// Textur Einstellungen
glTexImage2D(GL_TEXTURE_2D, 0, colors, surface->w, surface->h, 0, textureFormat, GL_UNSIGNED_BYTE, surface->pixels);

// Surface freilassen
SDL_FreeSurface(surface);

return texture;
}

Please ignore my German comments xD My problem is now that the light rotates with the box. I searched for that here and in Google. But nobody really has a answer. Can anybody help me or change my code so the light is constant? Phille Ps: I am learning English xD

hi,
My understanding is that lights must be positioned after the world is transform otherwise they also get transformed, so try puting the light code after the rotations. I might be wrong tho..

Thank you all for your answers.
Helped me a lot!

But the problem is not solved yet. It is still not working correct.
I read this: http://www.swiftless.com/tutorials/opengl/lighting_types.html
The code from that tutorial worked fine. Then I copied everything to one of my little examples with SDL and it didn't work any more. The same problem: The light is rotating.

Here is my new source code:

#include <SDL/SDL.h>#include <GL/glu.h>#include <GL/gl.h>void DrawScreen();GLfloat angle = 0.0;GLfloat dlr = 1.0;GLfloat dlg = 1.0;GLfloat dlb = 1.0;GLfloat alr = 1.0;GLfloat alg = 1.0;GLfloat alb = 1.0;GLfloat lx = 0.0;GLfloat ly = 0.0;GLfloat lz = 1.0;GLfloat lw = 0.0;int main(int argc, char* argv[]) {const SDL_VideoInfo* info = NULL;SDL_Surface *Surf_Window;SDL_Event event;int bpp;int width = 800, height = 600;bool active = true;if ( SDL_Init( SDL_INIT_VIDEO ) < 0 ) { return -1;}info = SDL_GetVideoInfo();bpp = info->vfmt->BitsPerPixel;SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);if((Surf_Window = SDL_SetVideoMode(width, height, bpp, SDL_OPENGL)) == NULL) {    return -1;}glShadeModel(GL_SMOOTH);glViewport(0, 0, width, height);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(60.0, width/height, 1.0, 100.0);glMatrixMode(GL_MODELVIEW);glEnable(GL_DEPTH_TEST);glEnable(GL_LIGHTING);glEnable(GL_LIGHT0);while(active) { while(SDL_PollEvent(&event)) {  switch(event.type) {   case SDL_KEYDOWN:    switch(event.key.keysym.sym) {     case SDLK_ESCAPE:      active = false;      break;    }    break;   case SDL_QUIT:    active = false;    break;  } } DrawScreen(); SDL_Delay(50);}SDL_Quit();return 0;}void DrawScreen() {glClearColor(0.0, 0.0, 0.0, 1.0);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glLoadIdentity();GLfloat DiffuseLight[] = {dlr, dlg, dlb};GLfloat AmbientLight[] = {alr, alg, alb};glLightfv(GL_LIGHT0, GL_DIFFUSE, DiffuseLight);glLightfv(GL_LIGHT0, GL_AMBIENT, AmbientLight);GLfloat LightPosition[] = {lx, ly, lz, lw};glLightfv(GL_LIGHT0, GL_POSITION, LightPosition);gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);glRotatef(angle, 1.0, 1.0, 1.0);glBegin(GL_QUADS); glVertex3f(-1.0f, 0.0, 1.0); glVertex3f(-1.0f, 0.0,-1.0); glVertex3f( 1.0f, 0.0,-1.0); glVertex3f( 1.0f, 0.0, 1.0);glEnd();glBegin(GL_TRIANGLES); glVertex3f(-1.0f, 0.0f, 1.0f); glVertex3f( 0.0f, 2.0f, 0.0f); glVertex3f(-1.0f, 0.0f,-1.0f); glVertex3f( 1.0f, 0.0f, 1.0f); glVertex3f( 0.0f, 2.0f, 0.0f); glVertex3f(-1.0f, 0.0f, 1.0f); glVertex3f( 1.0f, 0.0f,-1.0f); glVertex3f( 0.0f, 2.0f, 0.0f); glVertex3f( 1.0f, 0.0f, 1.0f); glVertex3f(-1.0f, 0.0f,-1.0f); glVertex3f( 0.0f, 2.0f, 0.0f); glVertex3f( 1.0f, 0.0f,-1.0f);glEnd();SDL_GL_SwapBuffers();angle++;if(angle >= 360) angle = 0;}

Should do it?! But it doesn't.
The only differences are that i am using SDL for my window handling and buffering instead for glut and that i am not using glutSolidCube(2); to create my object.
What is up with that??

Did I forget to set one SDL attribute?( SDL_GL_SetAttribute() -> http://www.libsdl.org/cgi/docwiki.cgi/SDL_GLattr)

I hope somebody can give me a solution. I am going crease!

Phille

anyone?

If not does somebody have a good sdl + opengl tutorial with a lighting lesson?
Could somebody compile my code and check if it's just my system or compiler that is wrong?