openGL Rotate Sphere with fix light - opengl

Question

i want to rotate a Sphere. And the light should be on a fix position in the room.
But it seems that the light is not on a fix position but rotate with the sphere.
I tried to put everything in push/popmatrix. Doesn't help.
I read about normal but I also read that glut does it automaticlly with spheres.
How can I fix the light position?
#include <windows.h>
#include <gl\gl.h>
#include <gl\glu.h>
#include <gl\glut.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
float angletest = 1;
float winwidth, winheight;
void keyboard(unsigned char key, int x, int y)
{
switch (key)
{
case'\033':
exit(0);
break;
}
}
void reshape(w, h)
GLsizei w;
GLsizei h;
{
int size;
winwidth = w;
winheight = h;
size = w>h ? h : w;
glViewport(0, 0, size, size);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(40, 1.0, 1.0f, 20.0f);
glutPostRedisplay();
}
void display(void)
{
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
glLoadIdentity();
GLUquadricObj *quadric;
quadric = gluNewQuadric();
glPushMatrix();
glColor3f(0, 0, 1);
glTranslatef(0.5, 0, 0);
glRotatef(angletest, 0, 0, 1);
gluSphere(quadric, 0.2, 50, 50);
glPopMatrix();
glPushMatrix();
glColor3f(0, 1, 0);
glRotatef(angletest, 0, 0, 1);
glTranslatef(0, 0.5, 0);
glutSolidSphere(0.2, 50, 50);
glPopMatrix();
glFlush();
glutSwapBuffers();
}
void init()
{
glEnable(GL_LIGHTING);
glEnable(GL_COLOR_MATERIAL);
glClearColor(0, 0, 0, 0);
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat mat_shininess[] = { 50.0 };
GLfloat light_position[] = { 0, 0.5, 0, 1.0f };
glShadeModel(GL_SMOOTH);
glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);
glLightfv(GL_LIGHT0, GL_POSITION, light_position);
glEnable(GL_LIGHT0);
}
void idle(void)
{
angletest = angletest + 0.05;
glutPostRedisplay();
}
void main(int argc, char** argv)
{
glutInitWindowSize(400, 400);
glutInitWindowPosition(100, 100);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("test");
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutKeyboardFunc(keyboard);
glutIdleFunc(idle);
init();
glutMainLoop();
}
Tried to do it like mentioned below and put the
glLightfv(GL_LIGHT0, GL_POSITION, light_position);
between glRotatef(angletest, 0, 0, 1); and gluSphere(quadric, 0.2, 50, 50);
But that didn't do it as well.
glPushMatrix();
glColor3f(0, 0, 1);
glTranslatef(0.5, 0, 0);
glRotatef(angletest, 0, 0, 1);
glLightfv(GL_LIGHT0, GL_POSITION, light_position);
gluSphere(quadric, 0.2, 50, 50);
glPopMatrix();
Actually, i wanted the lightsource to be in the middle. But if i put it in the position 0,0,0 there is no light at all.
To make clear what I mean by moving light, I have three pictures here.
light is in the right corner
light is in the left down corner
So you can see it seems like the light is moving with the objects.
But what I want is the light to stay in the middle and give lights to the object like if it was a sun.

Answer 1

Sorry, my comment was wrong. I just realized that you don't use the matrix stack to transform the camera (the view part in model-view) but the object space (the model part). glLightfv() should be called after you change the view part and before you change the model part. But you never change the view part in your code, so setting up the light once is sufficient.
There is another subtle problem in your code, which causes this behavior. Take a look at your reshape() function. You change the matrix mode to projection and never change it back to model-view. Hence, all matrix transformations that you apply are applied to the projection matrix. Lighting is calculated in view space. And since you do not change the model-view matrix, all lighting is done in the object's coordinate system (assuming the light position in this system). The projection matrix then rotates the already illuminated object, possibly away from the light.
So the solution is simple: Switch the matrix mode back to model-view in your reshape() function.