Is there a way to use glfwSetScrollCallback function inside a class?

Question

Hello I'm following opengl tutorial from this page and trying to implement a camera class. Here's my camera class code.

class Camera
{
public:
    
    static float fov;
    glm::vec3 pos;
    glm::vec3 front;
    glm::vec3 up;

    bool firstMouse;
    float screen_width;
    float screen_height;


    Camera(float screen_width, float screen_height);
    ~Camera();

    
    void setup_scroll_inputs(GLFWwindow* window);
    static void scroll_callback_static(GLFWwindow* window, double xoffset, double yoffset);
};

and cpp

void Camera::setup_scroll_inputs(GLFWwindow* window)
{
    glfwSetScrollCallback(window, Camera::scroll_callback_static);
}
void Camera::scroll_callback_static(GLFWwindow* window, double xoffset, double yoffset)
{
    fov -= (float)yoffset;
    if (fov < 20.0f)
        fov = 20.0f;
    if (fov > 100.0f)
        fov = 100.0f;
    
}

What I want to achieve is zoom-in and zoom-out feature whenever I scroll up or down. I tried to put glfwSetScrollCallback function in the camera class member function because I want to keep my main function as clean as possible. My scroll_callback function has to be a static member function since glfwSetScrollCallback is expecting a function pointer. However, I want to make it possible for the scroll_callback function to access camera's member variables. Is there a way to achieve this?

At the moment, I made fov to be a static member variable since my scrollback function would not have access to it otherwise.

Answer 1

A static function won't be able to access members of the class. You can use a non-capturing lambda to connect it

To access your camera object you'll need to store a pointer to it using glfwSetWindowUserPointer and retrieve it inside the lambda using glfwGetWindowUserPointer

glfwSetWindowUserPointer(window, &camera);
glfwSetScrollCallback(window, [](GLFWwindow* window,double xoffset, double yoffset) { 
    Camera* camera = (Camera*)glfwGetWindowUserPointer(window);
    camera->scroll_callback(window, xoffset, yoffset); 
});