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# Standards conformance {#compat_guide}
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[TOC]
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This guide describes the various API extensions used by this version of GLFW.
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It lists what are essentially implementation details, but which are nonetheless
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vital knowledge for developers intending to deploy their applications on a wide
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range of machines.
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The information in this guide is not a part of GLFW API, but merely
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preconditions for some parts of the library to function on a given machine. Any
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part of this information may change in future versions of GLFW and that will not
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be considered a breaking API change.
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## X11 extensions, protocols and IPC standards {#compat_x11}
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As GLFW uses Xlib directly, without any intervening toolkit library, it has sole
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responsibility for interacting well with the many and varied window managers in
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use on Unix-like systems. In order for applications and window managers to work
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well together, a number of standards and conventions have been developed that
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regulate behavior outside the scope of the X11 API; most importantly the
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[Inter-Client Communication Conventions Manual][ICCCM] (ICCCM) and [Extended
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Window Manager Hints][EWMH] (EWMH) standards.
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[ICCCM]: https://www.tronche.com/gui/x/icccm/
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[EWMH]: https://standards.freedesktop.org/wm-spec/wm-spec-latest.html
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GLFW uses the `_MOTIF_WM_HINTS` window property to support borderless windows.
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If the running window manager does not support this property, the
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`GLFW_DECORATED` hint will have no effect.
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GLFW uses the ICCCM `WM_DELETE_WINDOW` protocol to intercept the user
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attempting to close the GLFW window. If the running window manager does not
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support this protocol, the close callback will never be called.
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GLFW uses the EWMH `_NET_WM_PING` protocol, allowing the window manager notify
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the user when the application has stopped responding, i.e. when it has ceased to
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process events. If the running window manager does not support this protocol,
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the user will not be notified if the application locks up.
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GLFW uses the EWMH `_NET_WM_STATE_FULLSCREEN` window state to tell the window
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manager to make the GLFW window full screen. If the running window manager does
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not support this state, full screen windows may not work properly. GLFW has
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a fallback code path in case this state is unavailable, but every window manager
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behaves slightly differently in this regard.
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GLFW uses the EWMH `_NET_WM_BYPASS_COMPOSITOR` window property to tell a
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compositing window manager to un-redirect full screen GLFW windows. If the
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running window manager uses compositing but does not support this property then
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additional copying may be performed for each buffer swap of full screen windows.
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GLFW uses the [clipboard manager protocol][ClipboardManager] to push a clipboard
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string (i.e. selection) owned by a GLFW window about to be destroyed to the
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clipboard manager. If there is no running clipboard manager, the clipboard
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string will be unavailable once the window has been destroyed.
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[clipboardManager]: https://www.freedesktop.org/wiki/ClipboardManager/
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GLFW uses the [X drag-and-drop protocol][XDND] to provide file drop events. If
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the application originating the drag does not support this protocol, drag and
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drop will not work.
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[XDND]: https://www.freedesktop.org/wiki/Specifications/XDND/
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GLFW uses the XRandR 1.3 extension to provide multi-monitor support. If the
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running X server does not support this version of this extension, multi-monitor
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support will not function and only a single, desktop-spanning monitor will be
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reported.
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GLFW uses the XRandR 1.3 and Xf86vidmode extensions to provide gamma ramp
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support. If the running X server does not support either or both of these
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extensions, gamma ramp support will not function.
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GLFW uses the Xkb extension and detectable auto-repeat to provide keyboard
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input. If the running X server does not support this extension, a non-Xkb
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fallback path is used.
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GLFW uses the XInput2 extension to provide raw, non-accelerated mouse motion
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when the cursor is disabled. If the running X server does not support this
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extension, regular accelerated mouse motion will be used.
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GLFW uses both the XRender extension and the compositing manager to support
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transparent window framebuffers. If the running X server does not support this
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extension or there is no running compositing manager, the
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`GLFW_TRANSPARENT_FRAMEBUFFER` framebuffer hint will have no effect.
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GLFW uses both the Xcursor extension and the freedesktop cursor conventions to
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provide an expanded set of standard cursor shapes. If the running X server does
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not support this extension or the current cursor theme does not support the
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conventions, the `GLFW_RESIZE_NWSE_CURSOR`, `GLFW_RESIZE_NESW_CURSOR` and
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`GLFW_NOT_ALLOWED_CURSOR` shapes will not be available and other shapes may use
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legacy images.
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## Wayland protocols and IPC standards {#compat_wayland}
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As GLFW uses libwayland directly, without any intervening toolkit library, it
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has sole responsibility for interacting well with every compositor in use on
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Unix-like systems. Most of the features are provided by the core protocol,
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while cursor support is provided by the libwayland-cursor helper library, EGL
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integration by libwayland-egl, and keyboard handling by
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[libxkbcommon](https://xkbcommon.org/). In addition, GLFW uses some additional
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Wayland protocols to implement certain features if the compositor supports them.
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GLFW uses xkbcommon 0.5.0 to provide key and text input support. Earlier
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versions are not supported.
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GLFW uses the [xdg-shell][] protocol to provide better window management. This
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protocol is mandatory for GLFW to display a window.
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[xdg-shell]: https://wayland.app/protocols/xdg-shell
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GLFW uses the [relative-pointer-unstable-v1][] protocol alongside the
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[pointer-constraints-unstable-v1][] protocol to implement disabled cursor. If
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the running compositor does not support both of these protocols, disabling the
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cursor will have no effect.
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[relative-pointer-unstable-v1]: https://wayland.app/protocols/relative-pointer-unstable-v1
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[pointer-constraints-unstable-v1]: https://wayland.app/protocols/pointer-constraints-unstable-v1
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GLFW uses the [idle-inhibit-unstable-v1][] protocol to prohibit the screensaver
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from starting. If the running compositor does not support this protocol, the
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screensaver may start even for full screen windows.
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[idle-inhibit-unstable-v1]: https://wayland.app/protocols/idle-inhibit-unstable-v1
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GLFW uses the [libdecor][] library for window decorations, where available.
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This in turn provides good quality client-side decorations (drawn by the
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application) on desktop systems that do not support server-side decorations
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(drawn by the window manager). On systems that do not provide either libdecor
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or xdg-decoration, very basic window decorations are provided. These do not
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include the window title or any caption buttons.
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[libdecor]: https://gitlab.freedesktop.org/libdecor/libdecor
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GLFW uses the [xdg-decoration-unstable-v1][] protocol to request decorations to
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be drawn around its windows. This protocol is part of wayland-protocols 1.15,
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and mandatory at build time. If the running compositor does not support this
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protocol, a very simple frame will be drawn by GLFW itself, using the
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[viewporter][] protocol alongside subsurfaces. If the running compositor does
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not support these protocols either, no decorations will be drawn around windows.
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[xdg-decoration-unstable-v1]: https://wayland.app/protocols/xdg-decoration-unstable-v1
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[viewporter]: https://wayland.app/protocols/viewporter
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GLFW uses the [xdg-activation-v1][] protocol to implement window focus and
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attention requests. If the running compositor does not support this protocol,
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window focus and attention requests do nothing.
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[xdg-activation-v1]: https://wayland.app/protocols/xdg-activation-v1
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GLFW uses the [fractional-scale-v1][] protocol to implement fine-grained
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framebuffer scaling. If the running compositor does not support this protocol,
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the @ref GLFW_SCALE_FRAMEBUFFER window hint will only be able to scale the
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framebuffer by integer scales. This will typically be the smallest integer not
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less than the actual scale.
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[fractional-scale-v1]: https://wayland.app/protocols/fractional-scale-v1
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## GLX extensions {#compat_glx}
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The GLX API is the default API used to create OpenGL contexts on Unix-like
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systems using the X Window System.
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GLFW uses the GLX 1.3 `GLXFBConfig` functions to enumerate and select framebuffer pixel
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formats. If GLX 1.3 is not supported, @ref glfwInit will fail.
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GLFW uses the `GLX_MESA_swap_control,` `GLX_EXT_swap_control` and
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`GLX_SGI_swap_control` extensions to provide vertical retrace synchronization
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(or _vsync_), in that order of preference. When none of these extensions are
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available, calling @ref glfwSwapInterval will have no effect.
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GLFW uses the `GLX_ARB_multisample` extension to create contexts with
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multisampling anti-aliasing. Where this extension is unavailable, the
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`GLFW_SAMPLES` hint will have no effect.
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GLFW uses the `GLX_ARB_create_context` extension when available, even when
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creating OpenGL contexts of version 2.1 and below. Where this extension is
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unavailable, the `GLFW_CONTEXT_VERSION_MAJOR` and `GLFW_CONTEXT_VERSION_MINOR`
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hints will only be partially supported, the `GLFW_CONTEXT_DEBUG` hint will have
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no effect, and setting the `GLFW_OPENGL_PROFILE` or `GLFW_OPENGL_FORWARD_COMPAT`
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hints to `GLFW_TRUE` will cause @ref glfwCreateWindow to fail.
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GLFW uses the `GLX_ARB_create_context_profile` extension to provide support for
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context profiles. Where this extension is unavailable, setting the
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`GLFW_OPENGL_PROFILE` hint to anything but `GLFW_OPENGL_ANY_PROFILE`, or setting
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`GLFW_CLIENT_API` to anything but `GLFW_OPENGL_API` or `GLFW_NO_API` will cause
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@ref glfwCreateWindow to fail.
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GLFW uses the `GLX_ARB_context_flush_control` extension to provide control over
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whether a context is flushed when it is released (made non-current). Where this
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extension is unavailable, the `GLFW_CONTEXT_RELEASE_BEHAVIOR` hint will have no
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effect and the context will always be flushed when released.
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GLFW uses the `GLX_ARB_framebuffer_sRGB` and `GLX_EXT_framebuffer_sRGB`
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extensions to provide support for sRGB framebuffers. Where both of these
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extensions are unavailable, the `GLFW_SRGB_CAPABLE` hint will have no effect.
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## WGL extensions {#compat_wgl}
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The WGL API is used to create OpenGL contexts on Microsoft Windows and other
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implementations of the Win32 API, such as Wine.
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GLFW uses either the `WGL_EXT_extension_string` or the
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`WGL_ARB_extension_string` extension to check for the presence of all other WGL
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extensions listed below. If both are available, the EXT one is preferred. If
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neither is available, no other extensions are used and many GLFW features
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related to context creation will have no effect or cause errors when used.
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GLFW uses the `WGL_EXT_swap_control` extension to provide vertical retrace
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synchronization (or _vsync_). Where this extension is unavailable, calling @ref
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glfwSwapInterval will have no effect.
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GLFW uses the `WGL_ARB_pixel_format` and `WGL_ARB_multisample` extensions to
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create contexts with multisampling anti-aliasing. Where these extensions are
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unavailable, the `GLFW_SAMPLES` hint will have no effect.
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GLFW uses the `WGL_ARB_create_context` extension when available, even when
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creating OpenGL contexts of version 2.1 and below. Where this extension is
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unavailable, the `GLFW_CONTEXT_VERSION_MAJOR` and `GLFW_CONTEXT_VERSION_MINOR`
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hints will only be partially supported, the `GLFW_CONTEXT_DEBUG` hint will have
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no effect, and setting the `GLFW_OPENGL_PROFILE` or `GLFW_OPENGL_FORWARD_COMPAT`
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hints to `GLFW_TRUE` will cause @ref glfwCreateWindow to fail.
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GLFW uses the `WGL_ARB_create_context_profile` extension to provide support for
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context profiles. Where this extension is unavailable, setting the
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`GLFW_OPENGL_PROFILE` hint to anything but `GLFW_OPENGL_ANY_PROFILE` will cause
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@ref glfwCreateWindow to fail.
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GLFW uses the `WGL_ARB_context_flush_control` extension to provide control over
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whether a context is flushed when it is released (made non-current). Where this
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extension is unavailable, the `GLFW_CONTEXT_RELEASE_BEHAVIOR` hint will have no
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effect and the context will always be flushed when released.
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GLFW uses the `WGL_ARB_framebuffer_sRGB` and `WGL_EXT_framebuffer_sRGB`
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extensions to provide support for sRGB framebuffers. When both of these
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extensions are unavailable, the `GLFW_SRGB_CAPABLE` hint will have no effect.
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## OpenGL on macOS {#compat_osx}
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macOS (as of version 14) still provides OpenGL but it has been deprecated by
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Apple. While the API is still available, it is poorly maintained and frequently
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develops new issues. On modern systems, OpenGL is implemented on top of Metal
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and is not fully thread-safe.
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macOS does not support OpenGL stereo rendering. If the `GLFW_STEREO` hint is
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set to true, OpenGL context creation will always fail.
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macOS only supports OpenGL core profile contexts that are forward-compatible,
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but the `GLFW_OPENGL_FORWARD_COMPAT` hint is ignored since GLFW 3.4. Even if
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this hint is set to false (the default), a forward-compatible context will be
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returned if available.
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macOS does not support OpenGL debug contexts, no-error contexts or robustness.
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The `GLFW_CONTEXT_DEBUG`, `GLFW_CONTEXT_NO_ERROR` and `GLFW_CONTEXT_ROBUSTNESS`
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hints will be ignored and a context without these features will be returned.
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macOS does not flush OpenGL contexts when they are made non-current. The
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`GLFW_CONTEXT_RELEASE_BEHAVIOR` hint is ignored and the release behavior will
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always be the equivalent of `GLFW_RELEASE_BEHAVIOR_NONE`. If you need a context
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to be flushed, call `glFlush` before making it non-current.
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## Vulkan loader and API {#compat_vulkan}
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By default, GLFW uses the standard system-wide Vulkan loader to access the
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Vulkan API on all platforms except macOS. This is installed by both graphics
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drivers and Vulkan SDKs. If either the loader or at least one minimally
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functional ICD is missing, @ref glfwVulkanSupported will return `GLFW_FALSE` and
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all other Vulkan-related functions will fail with an @ref GLFW_API_UNAVAILABLE
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error.
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## Vulkan WSI extensions {#compat_wsi}
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The Vulkan WSI extensions are used to create Vulkan surfaces for GLFW windows on
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all supported platforms.
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GLFW uses the `VK_KHR_surface` and `VK_KHR_win32_surface` extensions to create
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surfaces on Microsoft Windows. If any of these extensions are not available,
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@ref glfwGetRequiredInstanceExtensions will return an empty list and window
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surface creation will fail.
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GLFW uses the `VK_KHR_surface` and either the `VK_MVK_macos_surface` or
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`VK_EXT_metal_surface` extensions to create surfaces on macOS. If any of these
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extensions are not available, @ref glfwGetRequiredInstanceExtensions will
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return an empty list and window surface creation will fail.
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GLFW uses the `VK_KHR_surface` and either the `VK_KHR_xlib_surface` or
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`VK_KHR_xcb_surface` extensions to create surfaces on X11. If `VK_KHR_surface`
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or both `VK_KHR_xlib_surface` and `VK_KHR_xcb_surface` are not available, @ref
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glfwGetRequiredInstanceExtensions will return an empty list and window surface
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creation will fail.
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GLFW uses the `VK_KHR_surface` and `VK_KHR_wayland_surface` extensions to create
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surfaces on Wayland. If any of these extensions are not available, @ref
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glfwGetRequiredInstanceExtensions will return an empty list and window surface
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creation will fail.
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