Making spotlight stationary - c++

Question

I'm trying to implement a pure stationary spotlight into my simple OpenGL scene, which doesn't move with the camera. It should keep highlighting the center of the scene (coords of 0,0,0), where I put the teapot.
Here is a simplified code:
#include <windows.h>
#define GLUT_DISABLE_ATEXIT_HACK
#include <gl/glut.h>
#include <gl/glu.h>
#include <gl/gl.h>
#include <math.h>
#include <iostream>
const int windowWidth = 640;
const int windowHeight = 480;
float alpha=0.0, alphaDelta=0.0, ratio, beta=0.0, betaDelta=0.0;
float x=0.0, y=1.75, z=5.0;
float lx=0.0, ly=0.0, lz=-1.0;
int moveDelta = 0;
float lastMouseX=windowWidth*0.5, lastMouseY=windowHeight*0.5;
void reshape(int w, int h){
//...
}
// handles angle changes
void orientMe(float horizontalAngle, float verticalAngle) {
lx = sin(horizontalAngle);
if(beta > -1.5 && beta < 1.5)
ly = sin(verticalAngle);
lz = -cos(horizontalAngle);
glLoadIdentity();
gluLookAt(x, y, z,
x + lx, y + ly, z + lz,
0.0, 1.0, 0.0);
}
// handles x,y,z coords changes
void flatMovement(int i) {
x = x + i*(lx)*0.1;
z = z + i*(lz)*0.1;
glLoadIdentity();
gluLookAt(x, y, z,
x + lx, y + ly, z + lz,
0.0, 1.0, 0.0);
}
void display() {
// orient observer
if(moveDelta)
flatMovement(moveDelta);
if(alphaDelta || betaDelta) {
alpha += alphaDelta;
alphaDelta = 0;
beta += betaDelta;
betaDelta = 0;
orientMe(alpha, beta);
}
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(0,1,0);
glBegin(GL_QUADS);
glNormal3d(0,1,0);
glVertex3f(-100.0, 0.0, -100.0);
glVertex3f(-100.0, 0.0, 100.0);
glVertex3f(100.0, 0.0, 100.0);
glVertex3f(100.0, 0.0, -100.0);
glEnd();
glColor3f(1,0,0);
glutSolidTeapot(1);
glutSwapBuffers();
}
void pressSpecialKey(int key, int x, int y) {
//...
}
void releaseSpecialKey(int key, int x, int y) {
//...
}
static void idle(void)
{
glutPostRedisplay();
}
void mouseMove(int x, int y) {
//...
}
void setupLights() {
GLfloat spotDirection[] = {0.0f, -1.0f, 0.0f, 1.0f};
GLfloat spotPosition[] = {0.0f, 4.0f, 0.0f, 1.0f};
glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 40);
glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, spotDirection);
glLightfv(GL_LIGHT0, GL_POSITION, spotPosition);
glEnable(GL_LIGHT0);
}
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitWindowSize(windowWidth,windowHeight);
glutInitWindowPosition(10,10);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("Spotlight");
glutSpecialFunc(pressSpecialKey);
glutSpecialUpFunc(releaseSpecialKey);
glutPassiveMotionFunc(mouseMove);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutIdleFunc(idle);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-5.0, 5.0, -5.0, 5.0, -5.0, 5.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glEnable(GL_LIGHTING);
glEnable(GL_NORMALIZE);
glEnable(GL_DEPTH_TEST);
setupLights();
glutMainLoop();
return EXIT_SUCCESS;
}
Unfortunately, the spotlight seems to follow camera changes and I have no idea what's wrong with the code above.
EDIT
Thanks to what #genpfault posted, I've alreadysorted things out.
The answer was to leave only the glEnable(GL_LIGHT0) in the main() function, and move the rest of the code responsible for lighting to the very end of the display() function (right before calling glutSwapBuffers().
So the final, simplified code looks as follows:
#include <windows.h>
#define GLUT_DISABLE_ATEXIT_HACK
#include <gl/glut.h>
#include <gl/glu.h>
#include <gl/gl.h>
#include <math.h>
#include <iostream>
const int windowWidth = 640;
const int windowHeight = 480;
float alpha=0.0, alphaDelta=0.0, ratio, beta=0.0, betaDelta=0.0;
float x=0.0, y=1.75, z=5.0;
float lx=0.0, ly=0.0, lz=-1.0;
int moveDelta = 0;
float lastMouseX=windowWidth*0.5, lastMouseY=windowHeight*0.5;
void reshape(int w, int h){
//...
}
// handles angle changes
void orientMe(float horizontalAngle, float verticalAngle) {
//...
}
// handles x,y,z coords changes
void flatMovement(int i) {
//...
}
void setupLights() {
//THE CONTENTS SLIGHTLY CHANGED HERE
GLfloat spotPosition[] = {2.0f, 4.0f, 0.0f, 1.0f};
GLfloat spotDirection[] = {0.0f, -1.0f, 0.0f, 1.0f};
glLightfv(GL_LIGHT0, GL_POSITION, spotPos
glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 40);ition);
glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, spotDirection);
}
void display() {
// orient observer
if(moveDelta)
flatMovement(moveDelta);
if(alphaDelta || betaDelta) {
alpha += alphaDelta;
alphaDelta = 0;
beta += betaDelta;
betaDelta = 0;
orientMe(alpha, beta);
}
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(0,1,0);
glBegin(GL_QUADS);
glNormal3d(0,1,0);
glVertex3f(-100.0, 0.0, -100.0);
glVertex3f(-100.0, 0.0, 100.0);
glVertex3f(100.0, 0.0, 100.0);
glVertex3f(100.0, 0.0, -100.0);
glEnd();
glColor3f(1,0,0);
glutSolidTeapot(1);
setupLights(); // PUT THE LIGHTING SETUP AT THE END OF DISPLAY()
glutSwapBuffers();
}
void pressSpecialKey(int key, int x, int y) {
//...
}
void releaseSpecialKey(int key, int x, int y) {
//...
}
static void idle(void)
{
glutPostRedisplay();
}
void mouseMove(int x, int y) {
//...
}
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitWindowSize(windowWidth,windowHeight);
glutInitWindowPosition(10,10);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("Spotlight");
glutSpecialFunc(pressSpecialKey);
glutSpecialUpFunc(releaseSpecialKey);
glutPassiveMotionFunc(mouseMove);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutIdleFunc(idle);
glEnable(GL_LIGHTING);
glEnable(GL_NORMALIZE);
glEnable(GL_DEPTH_TEST);
glEnable(GL_LIGHT0); // IN THE MAIN, LEAVE ONLY THE ENABLING CALL
glutMainLoop();
return EXIT_SUCCESS;
}

Answer 1

Set your light position after you set your camera transform:
void display()
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-5.0, 5.0, -5.0, 5.0, -5.0, 5.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
// orient observer
if(moveDelta)
flatMovement(moveDelta);
if(alphaDelta || betaDelta)
{
alpha += alphaDelta;
alphaDelta = 0;
beta += betaDelta;
betaDelta = 0;
orientMe(alpha, beta);
}
setupLights();
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(0,1,0);
glBegin(GL_QUADS);
glNormal3d(0,1,0);
glVertex3f(-100.0, 0.0, -100.0);
glVertex3f(-100.0, 0.0, 100.0);
glVertex3f(100.0, 0.0, 100.0);
glVertex3f(100.0, 0.0, -100.0);
glEnd();
glColor3f(1,0,0);
glutSolidTeapot(1);
glutSwapBuffers();
}
See here. Your existing code follows the "Moving the Light Source Together with Your Viewpoint" call sequence.