OpenGL Camera rotation problem

grafika.cpp

class Camera {
public:
    vec4 eye; // Specifies the position of the eye point.
    vec4 center; // Specifies the position of the reference point.
    vec4 up; // For tilting the camera
    float fov; // Field of view
    float near, far; // Near and far clipping plane
    Camera() {
        eye = vec4(0, 0, 2);
        center = vec4();
        up = vec4(0, 1, 0);
        fov = 45 * DEG2RAD;
        far = 100.0f;
        near = 0.1f;
    }

    mat4 V() { // View matrix glm::lookAt(eye, center, up)

        vec4 Z = (eye - center).normal();
        vec4 X = up % Z;
        vec4 Y = Z % X;

        return mat4(
                X.x(), Y.x(), Z.x(), 0.0f, // @          @
                X.y(), Y.y(), Z.y(), 0.0f, // @ Rotation @
                X.z(), Y.z(), Z.z(), 0.0f, // @          @
                X * eye, Y * eye, Z * eye, 1.0f // Translation
        );
    }

    mat4 P() { return Pers(); }

    mat4 Pers() { // Perspective Projection matrix
        float Q = far / (far - near);
        return mat4(1 / tanf(fov / 2), 0, 0, 0,
                    0, 1 / tanf(fov / 2), 0, 0,
                    0, 0, Q, 1,
                    0, 0, -Q * near, 1);
    }

    mat4 Portho() { // Orthogonal Projection matrix
        return mat4(
                1, 0, 0, 0,
                0, 1, 0, 0,
                0, 0, 1 / far, 0,
                0, 0, -(near + 1), 1
        );
    }
};

void onKeyboard(unsigned char key, int pX, int pY) {
    printf("Eye: %0.2f, %0.2f, %0.2f\n", camera.eye[0], camera.eye[1], camera.eye[2]);
    float theta = 2 * DEG2RAD;
    switch (key) {
        case 'q':
            exit(0);
        case 'a':
            camera.eye = camera.eye * mat4(
                    cosf(theta), 0, -sinf(theta), 0,
                    0, 1, 0, 0,
                    sinf(theta), 0, cosf(theta), 0,
                    0, 0, 0, 1
            );
            break;
        case 'd':
            camera.eye = camera.eye * mat4(
                    cosf(-theta), 0, -sinf(-theta), 0,
                    0, 1, 0, 0,
                    sinf(-theta), 0, cosf(-theta), 0,
                    0, 0, 0, 1
            );
            break;
        case 'w':
            camera.eye = camera.eye * mat4(
                    1, 0, 0, 0,
                    0, cosf(theta), sinf(theta), 0,
                    0, -sinf(theta), cosf(theta), 0,
                    0, 0, 0, 1
            );
            break;
        case 's':
            camera.eye = camera.eye * mat4(
                    1, 0, 0, 0,
                    0, cosf(-theta), sinf(-theta), 0,
                    0, -sinf(-theta), cosf(-theta), 0,
                    0, 0, 0, 1
            );
            break;
        default:
            break;
    }
}