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Phille

OpenGL OpenGL Lighting Problem

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Phille    122
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

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cherryyosh    100
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..

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David_pb    1046
As for sunlight: You should possibly think about a directional light in this case. It's not a big deal, all you've to do is to set 'w' for your lightpos to 0.

Ps: Wieso denn? Die Kommentare sind doch total interessant? :-O

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Phille    122
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

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Phille    122
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?

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