GLFW: size, position & monitorsGLFW 3.0

glfwSetWindowUserPointer

Attaches one pointer of your own to the window, so callbacks can reach your objects without globals.

Signature

void glfwSetWindowUserPointer(GLFWwindow* window, void* pointer);

How it works

GLFW callbacks are plain C functions: they receive the window and the event, nothing else. If the key callback must move a camera, how does it find the camera? The quick answer is a global variable; the clean one is the user pointer.

Store a pointer to your app object once, then read it back inside any callback with glfwGetWindowUserPointer. GLFW never looks at it or frees it.

Parameters

windowGLFWwindow*

The window to attach the pointer to.

pointervoid*

Any pointer, usually this or the address of your app struct. Starts as NULL.

Tips & pitfalls

The object must live as long as the window, or callbacks will read a dangling pointer.

Errors

When the call is invalid it does nothing and sets an error, which glGetError returns:

GLFW_NOT_INITIALIZED: Called before glfwInit or after glfwTerminate.

Example

example.cpp

1struct App { Camera camera; };
2App app;
3glfwSetWindowUserPointer(window, &app);
4glfwSetScrollCallback(window, [](GLFWwindow* w, double, double dy) {
5    auto* app = static_cast<App*>(glfwGetWindowUserPointer(w));
6    app->camera.zoom(dy);
7});

Official GLFW documentation