Finding a spotlight vector in openGL - c

Question

I'm trying to find the proper vector for a direction of a spot light I have (I am trying to make it flashlight-like). I want it to face the same direction as the camera is always facing, like you're holding a flashlight out in front of you.
I can't seem to find the right directional vector, however.
At the moment, I have the light sort of following the front/back movement of the camera, but not the turn angle. In addition, the actual spot is pointed upwards, instead of directly ahead, like I want.
I know all the normals of the individual objects are working; I tested just general lighting already.
I'll just post code that's relevant to the question. If you really need my whole code, please say so.
Light code:
float sco=20; // Spot cutoff angle
float Exp=0; // Spot exponent
float Ambient[] = {0.01*ambient ,0.01*ambient ,0.01*ambient ,1.0};
float Diffuse[] = {0.01*diffuse ,0.01*diffuse ,0.01*diffuse ,1.0};
float Specular[] = {0.01*specular,0.01*specular,0.01*specular,1.0};
// Light direction
float Position[] = {Ox+3, 2, Oz,1};
float Direction[] = {Ox+lx, here, Oz+lz, 0};
glLightfv(GL_LIGHT0,GL_AMBIENT ,Ambient);
glLightfv(GL_LIGHT0,GL_DIFFUSE ,Diffuse);
glLightfv(GL_LIGHT0,GL_SPECULAR,Specular);
glLightfv(GL_LIGHT0,GL_POSITION,Position);
glLightfv(GL_LIGHT0,GL_SPOT_DIRECTION,Direction);
glLightf(GL_LIGHT0,GL_SPOT_CUTOFF,sco);
glLightf(GL_LIGHT0,GL_SPOT_EXPONENT,Exp);
Camera code:
// Camera Values
double Ox=0, Oz=0;
float Oy=1.0;
float angle = 0.0;
float lx=0.0,lz=-1.0;
float deltaAngle = 0.0;
float deltaMove = 0;
double here;
void computePos(float deltaMove) {
Ox += deltaMove * lx * 0.1f;
Oz += deltaMove * lz * 0.1f;
}
void computeDir(float deltaAngle) {
angle += deltaAngle;
lx = sin(angle);
lz = -cos(angle);
}
void display() {
here = 2.0f*Oy;
if (deltaMove)
computePos(deltaMove);
if (deltaAngle)
computeDir(deltaAngle);
gluLookAt(Ox,2,Oz, Ox+lx, here, Oz+lz, 0,1,0);
}
void key(unsigned char ch,int x,int y) {
// Exit on ESC
if (ch == 27)
exit(0);
// WASD controls
else if (ch == 'a' || ch == 'A')
deltaAngle = -0.01;
else if (ch == 'd' || ch == 'D')
deltaAngle = 0.01;
else if (ch == 'w' || ch == 'W') {
collidefront=collision(1);
collidextra=collision(3);
if (collideback == 2 && collidextra == 3) { deltaMove = 0; collideback = 0; }
else if (collideback == 2) { deltaMove = 0.1; collidefront = 0;}
else if (collidefront == 1) deltaMove = 0;
else
deltaMove = 0.1;
}
else if (ch == 's' || ch == 'S') {
collideback=collision(2);
if (collidefront == 1) { deltaMove = -0.3; collidefront = 0; }
else if (collideback == 2) deltaMove = 0;
else
deltaMove = -0.1;
}
else if ((ch == 'e' || ch == 'E') && here < 4)
Oy += 0.01;
else if ((ch == 'c' || ch == 'C') && here > .5)
Oy -= 0.01;
Project(fov,asp,dim);
glutPostRedisplay();
}
Thank you for your help.

Answer 1

Since you are using gluLookAt, you can easily compute the vector subtracting the center and the eye:
(...)
gluLookAt(eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ);
(...)
spotlightVecX = centerX - eyeX;
spotlightVecY = centerY - eyeY;
spotlightVecZ = centerZ - eyeZ;
You may normalize it after you calculate the vector.
Hope it helps.