GLFW: Standards conformance

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Standards conformance

This guide describes the various API extensions used by this version of GLFW. It lists what are essentially implementation details, but which are nonetheless vital knowledge for developers intending to deploy their applications on a wide range of machines.

The information in this guide is not a part of GLFW API, but merely preconditions for some parts of the library to function on a given machine. Any part of this information may change in future versions of GLFW and that will not be considered a breaking API change.

# X11 extensions, protocols and IPC standards

As GLFW uses Xlib directly, without any intervening toolkit library, it has sole responsibility for interacting well with the many and varied window managers in use on Unix-like systems. In order for applications and window managers to work well together, a number of standards and conventions have been developed that regulate behavior outside the scope of the X11 API; most importantly the Inter-Client Communication Conventions Manual (ICCCM) and Extended Window Manager Hints (EWMH) standards.

GLFW uses the _MOTIF_WM_HINTS window property to support borderless windows. If the running window manager does not support this property, the GLFW_DECORATED hint will have no effect.

GLFW uses the ICCCM WM_DELETE_WINDOW protocol to intercept the user attempting to close the GLFW window. If the running window manager does not support this protocol, the close callback will never be called.

GLFW uses the EWMH _NET_WM_PING protocol, allowing the window manager notify the user when the application has stopped responding, i.e. when it has ceased to process events. If the running window manager does not support this protocol, the user will not be notified if the application locks up.

GLFW uses the EWMH _NET_WM_STATE_FULLSCREEN window state to tell the window manager to make the GLFW window full screen. If the running window manager does not support this state, full screen windows may not work properly. GLFW has a fallback code path in case this state is unavailable, but every window manager behaves slightly differently in this regard.

GLFW uses the EWMH _NET_WM_BYPASS_COMPOSITOR window property to tell a compositing window manager to un-redirect full screen GLFW windows. If the running window manager uses compositing but does not support this property then additional copying may be performed for each buffer swap of full screen windows.

GLFW uses the clipboard manager protocol to keep the clipboard string availble for the user after the libary has been terminated. If there is no running clipboard manager and the clipboard contents has been set with glfwSetClipboardString, the clipboard will be emptied when the library is terminated.

GLFW uses the X drag-and-drop protocol to provide file drop events. If the application originating the drag does not support this protocol, drag and drop will not work.

GLFW uses the XRandR 1.3 extension to provide multi-monitor support. If the running X server does not support this version of this extension, multi-monitor support will not function and only a single, desktop-spanning monitor will be reported.

GLFW uses the XRandR 1.3 and Xf86vidmode extensions to provide gamma ramp support. If the running X server does not support either or both of these extensions, gamma ramp support will not function.

GLFW uses the Xkb extension and detectable auto-repeat to provide keyboard input. If the running X server does not support this extension, a non-Xkb fallback path is used.

GLFW uses the XInput2 extension to provide raw, non-accelerated mouse motion when the cursor is disabled. If the running X server does not support this extension, regular accelerated mouse motion will be used.

GLFW uses both the XRender extension and the compositing manager to support transparent window framebuffers. If the running X server does not support this extension or there is no running compositing manager, the GLFW_TRANSPARENT_FRAMEBUFFER framebuffer hint will have no effect.

GLFW uses both the Xcursor extension and the freedesktop cursor conventions to provide an expanded set of standard cursor shapes. If the running X server does not support this extension or the current cursor theme does not support the conventions, the GLFW_RESIZE_NWSE_CURSOR, GLFW_RESIZE_NESW_CURSOR and GLFW_NOT_ALLOWED_CURSOR shapes will not be available and other shapes may use legacy images.

# Wayland protocols and IPC standards

As GLFW uses libwayland directly, without any intervening toolkit library, it has sole responsibility for interacting well with every compositor in use on Unix-like systems. Most of the features are provided by the core protocol, while cursor support is provided by the libwayland-cursor helper library, EGL integration by libwayland-egl, and keyboard handling by libxkbcommon. In addition, GLFW uses some additional Wayland protocols to implement certain features if the compositor supports them.

GLFW uses xkbcommon 0.5.0 to provide key and text input support. Earlier versions are not supported.

GLFW uses the xdg-shell protocol to provide better window management. This protocol is mandatory for GLFW to display a window.

GLFW uses the relative-pointer-unstable-v1 protocol alongside the pointer-constraints-unstable-v1 protocol to implement disabled cursor. If the running compositor does not support both of these protocols, disabling the cursor will have no effect.

GLFW uses the idle-inhibit-unstable-v1 protocol to prohibit the screensaver from starting. If the running compositor does not support this protocol, the screensaver may start even for full screen windows.

GLFW uses the libdecor library for window decorations, where available. This in turn provides good quality client-side decorations (drawn by the application) on desktop systems that do not support server-side decorations (drawn by the window manager). On systems that do not provide either libdecor or xdg-decoration, very basic window decorations are provided. These do not include the window title or any caption buttons.

GLFW uses the xdg-decoration-unstable-v1 protocol to request decorations to be drawn around its windows. This protocol is part of wayland-protocols 1.15, and mandatory at build time. If the running compositor does not support this protocol, a very simple frame will be drawn by GLFW itself, using the viewporter protocol alongside subsurfaces. If the running compositor does not support these protocols either, no decorations will be drawn around windows.

GLFW uses the xdg-activation-v1 protocol to implement window focus and attention requests. If the running compositor does not support this protocol, window focus and attention requests do nothing.

GLFW uses the fractional-scale-v1 protocol to implement fine-grained framebuffer scaling. If the running compositor does not support this protocol, the GLFW_SCALE_FRAMEBUFFER window hint will only be able to scale the framebuffer by integer scales. This will typically be the smallest integer not less than the actual scale.

# GLX extensions

The GLX API is the default API used to create OpenGL contexts on Unix-like systems using the X Window System.

GLFW uses the GLX 1.3 GLXFBConfig functions to enumerate and select framebuffer pixel formats. If GLX 1.3 is not supported, glfwInit will fail.

GLFW uses the GLX_MESA_swap_control, GLX_EXT_swap_control and GLX_SGI_swap_control extensions to provide vertical retrace synchronization (or vsync), in that order of preference. When none of these extensions are available, calling glfwSwapInterval will have no effect.

GLFW uses the GLX_ARB_multisample extension to create contexts with multisampling anti-aliasing. Where this extension is unavailable, the GLFW_SAMPLES hint will have no effect.

GLFW uses the GLX_ARB_create_context extension when available, even when creating OpenGL contexts of version 2.1 and below. Where this extension is unavailable, the GLFW_CONTEXT_VERSION_MAJOR and GLFW_CONTEXT_VERSION_MINOR hints will only be partially supported, the GLFW_CONTEXT_DEBUG hint will have no effect, and setting the GLFW_OPENGL_PROFILE or GLFW_OPENGL_FORWARD_COMPAT hints to GLFW_TRUE will cause glfwCreateWindow to fail.

GLFW uses the GLX_ARB_create_context_profile extension to provide support for context profiles. Where this extension is unavailable, setting the GLFW_OPENGL_PROFILE hint to anything but GLFW_OPENGL_ANY_PROFILE, or setting GLFW_CLIENT_API to anything but GLFW_OPENGL_API or GLFW_NO_API will cause glfwCreateWindow to fail.

GLFW uses the GLX_ARB_context_flush_control extension to provide control over whether a context is flushed when it is released (made non-current). Where this extension is unavailable, the GLFW_CONTEXT_RELEASE_BEHAVIOR hint will have no effect and the context will always be flushed when released.

GLFW uses the GLX_ARB_framebuffer_sRGB and GLX_EXT_framebuffer_sRGB extensions to provide support for sRGB framebuffers. Where both of these extensions are unavailable, the GLFW_SRGB_CAPABLE hint will have no effect.

# WGL extensions

The WGL API is used to create OpenGL contexts on Microsoft Windows and other implementations of the Win32 API, such as Wine.

GLFW uses either the WGL_EXT_extension_string or the WGL_ARB_extension_string extension to check for the presence of all other WGL extensions listed below. If both are available, the EXT one is preferred. If neither is available, no other extensions are used and many GLFW features related to context creation will have no effect or cause errors when used.

GLFW uses the WGL_EXT_swap_control extension to provide vertical retrace synchronization (or vsync). Where this extension is unavailable, calling glfwSwapInterval will have no effect.

GLFW uses the WGL_ARB_pixel_format and WGL_ARB_multisample extensions to create contexts with multisampling anti-aliasing. Where these extensions are unavailable, the GLFW_SAMPLES hint will have no effect.

GLFW uses the WGL_ARB_create_context extension when available, even when creating OpenGL contexts of version 2.1 and below. Where this extension is unavailable, the GLFW_CONTEXT_VERSION_MAJOR and GLFW_CONTEXT_VERSION_MINOR hints will only be partially supported, the GLFW_CONTEXT_DEBUG hint will have no effect, and setting the GLFW_OPENGL_PROFILE or GLFW_OPENGL_FORWARD_COMPAT hints to GLFW_TRUE will cause glfwCreateWindow to fail.

GLFW uses the WGL_ARB_create_context_profile extension to provide support for context profiles. Where this extension is unavailable, setting the GLFW_OPENGL_PROFILE hint to anything but GLFW_OPENGL_ANY_PROFILE will cause glfwCreateWindow to fail.

GLFW uses the WGL_ARB_context_flush_control extension to provide control over whether a context is flushed when it is released (made non-current). Where this extension is unavailable, the GLFW_CONTEXT_RELEASE_BEHAVIOR hint will have no effect and the context will always be flushed when released.

GLFW uses the WGL_ARB_framebuffer_sRGB and WGL_EXT_framebuffer_sRGB extensions to provide support for sRGB framebuffers. When both of these extensions are unavailable, the GLFW_SRGB_CAPABLE hint will have no effect.

# OpenGL on macOS

macOS (as of version 14) still provides OpenGL but it has been deprecated by Apple. While the API is still available, it is poorly maintained and frequently develops new issues. On modern systems, OpenGL is implemented on top of Metal and is not fully thread-safe.

macOS does not support OpenGL stereo rendering. If the GLFW_STEREO hint is set to true, OpenGL context creation will always fail.

macOS only supports OpenGL core profile contexts that are forward-compatible, but the GLFW_OPENGL_FORWARD_COMPAT hint is ignored since GLFW 3.4. Even if this hint is set to false (the default), a forward-compatible context will be returned if available.

macOS does not support OpenGL debug contexts, no-error contexts or robustness. The GLFW_CONTEXT_DEBUG, GLFW_CONTEXT_NO_ERROR and GLFW_CONTEXT_ROBUSTNESS hints will be ignored and a context without these features will be returned.

macOS does not flush OpenGL contexts when they are made non-current. The GLFW_CONTEXT_RELEASE_BEHAVIOR hint is ignored and the release behavior will always be the equivalent of GLFW_RELEASE_BEHAVIOR_NONE. If you need a context to be flushed, call glFlush before making it non-current.

# Vulkan loader and API

By default, GLFW uses the standard system-wide Vulkan loader to access the Vulkan API on all platforms except macOS. This is installed by both graphics drivers and Vulkan SDKs. If either the loader or at least one minimally functional ICD is missing, glfwVulkanSupported will return GLFW_FALSE and all other Vulkan-related functions will fail with an GLFW_API_UNAVAILABLE error.

# Vulkan WSI extensions

The Vulkan WSI extensions are used to create Vulkan surfaces for GLFW windows on all supported platforms.

GLFW uses the VK_KHR_surface and VK_KHR_win32_surface extensions to create surfaces on Microsoft Windows. If any of these extensions are not available, glfwGetRequiredInstanceExtensions will return an empty list and window surface creation will fail.

GLFW uses the VK_KHR_surface and either the VK_MVK_macos_surface or VK_EXT_metal_surface extensions to create surfaces on macOS. If any of these extensions are not available, glfwGetRequiredInstanceExtensions will return an empty list and window surface creation will fail.

GLFW uses the VK_KHR_surface and either the VK_KHR_xlib_surface or VK_KHR_xcb_surface extensions to create surfaces on X11. If VK_KHR_surface or both VK_KHR_xlib_surface and VK_KHR_xcb_surface are not available, glfwGetRequiredInstanceExtensions will return an empty list and window surface creation will fail.

GLFW uses the VK_KHR_surface and VK_KHR_wayland_surface extensions to create surfaces on Wayland. If any of these extensions are not available, glfwGetRequiredInstanceExtensions will return an empty list and window surface creation will fail.