GLFW: size, position & monitorsGLFW 3.0

glfwSetFramebufferSizeCallback

Registers a function GLFW calls whenever the framebuffer changes size, so you can update glViewport.

Signature

GLFWframebuffersizefun glfwSetFramebufferSizeCallback(GLFWwindow* window, GLFWframebuffersizefun callback);

How it works

When the user resizes the window (or drags it to a monitor with another scale), the framebuffer gets a new size, but the viewport keeps the old one. The picture then looks stretched or cut off.

The callback receives the window and the new width and height in pixels. The classic body is a single glViewport call. Projection matrices that use the aspect ratio should read the new size too.

Parameters

windowGLFWwindow*

The window to watch.

callbackGLFWframebuffersizefun

Your function, void f(GLFWwindow* window, int width, int height), or NULL to remove it.

Return value

The callback that was set before, or NULL.

Tips & pitfalls

It runs inside glfwPollEvents, on the main thread, with the context still current: gl* calls are fine there.
It is NOT called for the initial size. Call glViewport once yourself after creating the window.
Prefer it over glfwSetWindowSizeCallback for the viewport: that one reports screen coordinates, not pixels.

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

1void onFramebufferSize(GLFWwindow*, int w, int h) {
2    glViewport(0, 0, w, h);
3}
4
5glfwSetFramebufferSizeCallback(window, onFramebufferSize);

Official GLFW documentation