OpenGl GluLookAt to GlRotated and GlTranslated - opengl

Question

I dont understand how this GluLookAt works in OpenGl.
I would like to know how to transform this two lines :
gluLookAt(5.0, 15.0, 2.0, 0.0, 0.0, 0.0, 1.0, 0.0, -1.0);
gluLookAt(5.0, 0.0, 5.0, 0.0, 0.0, 0.0, 1.0, -1.0, 0.0);
using glRotatef and glTranslatef.
After some searches, it seems to exist a way for making that thing :
glRotatef();
glRotatef();
glTranslatef(5.0,15.0,2.0);
glRotatef();
glRotatef();
glTranslatef(5.0,0.0,5.0);
So just by using two rotations and one translation.
But I dont understand how can i find the angles and the axes of these rotations.

Answer 1

I tried to explain how the functions work below. Hope it makes you understand the concept. For rotation and translation you can check this link to see how it is handled.
struct Triple
{
float x,y,z;
}
//CameraPosition
Triple Cp(a,b,c); //initialise your camera position
//LookatPosition
Triple Lp(e,f,g); //initialise your lookat position
//Up vector
Triple Up(k,l,m); //initialise your up vector
UpdateCamera()
{
//Update Cp, Lp here
//if you move your camera use translatef to update camera position
//if you want to change looking direction use correct rotation and translation to update your lookat position
//if you need to change up vector simply change it to
Up = Triple(knew,lnew,mnew);
}
display()
{
gluLookAt(Cp.x,Cp.y,Cp.z,Lp.x,Lp.y,Lp.z,Up.x,Up.y,Up.z);
//Your object drawings Here
}

Answer 2

I'd like to sidestep the glRotate and glTranslate and use glLoadMatrix instead (glLoadMatrix replaces the current matrix on the stack use glMultMatrix if you want to multiply): you would then use an array of floats containing the matrix in column major order:
xaxis.x yaxis.x zaxis.x 0
xaxis.y yaxis.y zaxis.y 0
xaxis.z yaxis.z zaxis.z 0
-dot(xaxis, camP) -dot(yaxis, camP) -dot(zaxis, camP) 1
where
zaxis = normal(At - camP)
xaxis = normal(cross(Up, zaxis))
yaxis = cross(zaxis, xaxis)
and camP the position of the camera, At the point the camera is looking at and Up the up-vector.