GLKMathProject and GLKMathUnproject

GLKMathUtils

GLKVector3 GLKMathProject(GLKVector3 object, GLKMatrix4 model, GLKMatrix4 projection, int *viewport) {
    assert(viewport);
    
    GLKVector4 v4 = GLKVector4MakeWithVector3(object, 1.0);
    GLKVector4 v = GLKMatrix4MultiplyVector4(model, v4);
    v = GLKMatrix4MultiplyVector4(projection, v);
    
    v.v[3] = 1.0/v.v[3];
    v.v[0] *= v.v[3];
    v.v[1] *= v.v[3];
    v.v[2] *= v.v[3];
    
    float x = (v.v[0] * 0.5 + 0.5) * viewport[2] + viewport[0];
    float y = (v.v[1] * 0.5 + 0.5) * viewport[3] + viewport[1];
    float z = (1.0 + v.v[2])*0.5;

    return GLKVector3Make(x, y, z);
}

GLKVector3 GLKMathUnproject(GLKVector3 window, GLKMatrix4 model, GLKMatrix4 projection, int *viewport, bool *success) {
    assert(viewport);
    bool canInvert = false;
    GLKMatrix4 inverted = GLKMatrix4Invert(GLKMatrix4Multiply(projection, model), &canInvert);
    if (success) {
        *success = canInvert;
    }
    
    if (!canInvert) {
        return GLKVector3Make(0.0f, 0.0f, 0.0f);
    }
    
    GLKVector4 normalisedVector = GLKVector4Make((2 * window.x / viewport[2] - 1),
                                                 (2 * (window.y - viewport[1]) / viewport[3] - 1),
                                                 2*window.z - 1,
                                                 1);
    
    GLKVector4 _point = GLKMatrix4MultiplyVector4(inverted, normalisedVector);
    _point.v[3] = 1.0/_point.v[3];
    
    GLKVector3 vec = GLKVector3Make(_point.v[0]*_point.v[3], _point.v[1]*_point.v[3], _point.v[2]*_point.v[3]);

    return vec;
}