GluUnproject works, but only when the camera is not rotated

Question

I am working on a very basic 3D program, my first one using OpenGL. What I am trying to do is trace a ray from the mouse's location on click which works, but only when the camera is not rotated. When the camera is rotated, the unproject treats it as if it was not.

What am I doing wrong?

The code for unproject:

Coord3<GLdouble> Display::GetOGLPos(uint16_t x, uint16_t y)
{
    GLint viewport[4];
    GLdouble modelview[16];
    GLdouble projection[16];

    Coord2<GLfloat> window_location;
    Coord3<GLdouble> resultant_ray;

    glGetDoublev(GL_MODELVIEW_MATRIX, modelview);
    glGetDoublev(GL_PROJECTION_MATRIX, projection);
    glGetIntegerv(GL_VIEWPORT, viewport);

    window_location.x = (float)x;
    window_location.y = viewport[3] - (float)y;

    gluUnProject(window_location.x , window_location.y, 1.0f, modelview, projection, viewport, &resultant_ray.x, &resultant_ray.y, &resultant_ray.z);

    return resultant_ray;
}

The display code:

void Display::Render()
{
    if(!dirty)
    {
        return;
    }

    glTranslatef(camera.location.x ,camera.location.y, camera.location.z);

    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    glRotatef(camera.angle.y, 1, 0, 0);
    glRotatef(camera.angle.x, 0, 1, 0);

    glCallList(cube);

    glColor3ub(0, 0, 255);

    glBegin(GL_LINES);
    glVertex3f(0,0,0);
    glVertex3f(mouse_click.x, mouse_click.y, mouse_click.z);
    glEnd();

    glLoadIdentity();

    SDL_GL_SwapBuffers();

    dirty = 0;

    SDL_Delay(33);
}

Answer 1

It might be because you're clearing the modelview matrix at the end of draw() with glLoadIdentity(); Try doing the transformations again at the beginning of GetOGLPos before you call glGetDoublev() for the matrices, then loading the identity matrix afterwards.