nano_camera.h

struct NanoCamera
{
    float rotx = 0.f;
    float roty = 0.f;
    float zoom = 0.f;
    float fovy = 75.f;

    glm::mat4 view = glm::identity<glm::mat4>();
    glm::mat4 proj = glm::identity<glm::mat4>();

    glm::mat4 update(float aspect, float displ_x, float displ_y, float wheel_y)
    {
        rotx += displ_x * 0.001f;
        roty += displ_y * 0.001f;
        zoom += wheel_y;

        glm::mat4 pivot = glm::identity<glm::mat4>();
        pivot           = glm::rotate(pivot, rotx, glm::vec3 { 0, 1, 0 });
        pivot           = glm::rotate(pivot, roty, glm::vec3 { 1, 0, 0 });

        glm::vec3 const front = -1.f * pivot[2].xyz();
        glm::vec3 const eye   = front * zoom;
        view                  = glm::lookAt(eye, eye + front, pivot[1].xyz());
        proj                  = glm::perspective(fovy, aspect, 0.1f, 1'000.f);

        return proj * view;
    }
};