void beginPerspectiveProjection(){
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();

    double fov, near, far;
    double headX, headY, headZ;
    float aspectRatio;

    near = 0.5f; far = 1000.0f;  aspectRatio = ofGetWidth()/ofGetHeight();
    fov = tan(DEG_TO_RAD * 30/2); //tan accepts angle in radians. tan of the half of the fov angle
    fov = 0.5;

    double msX = (double)ofGetMouseX();
    double msY = (double)ofGetMouseY();
    double scrWidth = (double)ofGetWidth();
    double scrHeight = (double)ofGetHeight();

    headX = (msX / scrWidth) - 0.5;
    headY = ((scrHeight - msY) / scrHeight) - 0.5;
    headZ = -2.0;

    glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glFrustum( near * (-fov * aspectRatio + headX),
                   near * (fov * aspectRatio + headX),
                   near * (-fov + headY),
                   near * (fov + headY),
                   near,
                   far
                  );
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(headX * headZ, headY * headZ, 0, headX * headZ, headY * headZ, -1, 0, 1, 0);
    glTranslatef(0.0, 0.0, headZ);
}