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 push a clipboard string (i.e. selection) owned by a GLFW window about to be destroyed to the clipboard manager. If there is no running clipboard manager, the clipboard string will be unavailable once the window has been destroyed.

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.

# 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 protocols from wayland-protocols to provide additional features if the compositor supports them.

GLFW uses xkbcommon 0.5.0 to provide compose key support. When it has been built against an older xkbcommon, the compose key will be disabled even if it has been configured in the compositor.

GLFW uses the xdg-shell protocol to provide better window management. This protocol is part of wayland-protocols 1.12, and mandatory at build time. If the running compositor does not support this protocol, the older wl_shell interface will be used instead. This will result in a worse integration with the desktop, especially on tiling compositors.

GLFW uses the relative pointer protocol alongside the pointer constraints protocol to implement disabled cursor. These two protocols are part of wayland-protocols 1.1, and mandatory at build time. If the running compositor does not support both of these protocols, disabling the cursor will have no effect.

GLFW uses the idle inhibit protocol to prohibit the screensaver from starting. This protocol is part of wayland-protocols 1.6, and mandatory at build time. If the running compositor does not support this protocol, the screensaver may start even for full screen windows.

GLFW uses the xdg-decoration 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. This protocol is part of wayland-protocols 1.4, and mandatory at build time. If the running compositor does not support this protocol either, no decorations will be drawn around windows.

# 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. Where none of these extension 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_OPENGL_DEBUG_CONTEXT` 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_OPENGL_DEBUG_CONTEXT` 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. Where both of these extension are unavailable, the `GLFW_SRGB_CAPABLE` hint will have no effect.

# OpenGL on macOS

Support for OpenGL 3.2 and above was introduced with OS X 10.7 and even then only forward-compatible, core profile contexts are supported. Support for OpenGL 4.1 was introduced with OS X 10.9, also limited to forward-compatible, core profile contexts. There is also still no mechanism for requesting debug contexts or no-error contexts. Versions of Mac OS X earlier than 10.7 support at most OpenGL version 2.1.

Because of this, on OS X 10.7 and later, the `GLFW_CONTEXT_VERSION_MAJOR` and `GLFW_CONTEXT_VERSION_MINOR` hints will cause glfwCreateWindow to fail if given version 3.0 or 3.1. The `GLFW_OPENGL_FORWARD_COMPAT` hint must be set to `GLFW_TRUE` and the `GLFW_OPENGL_PROFILE` hint must be set to `GLFW_OPENGL_CORE_PROFILE` when creating OpenGL 3.2 and later contexts. The `GLFW_OPENGL_DEBUG_CONTEXT` and `GLFW_CONTEXT_NO_ERROR` hints are ignored.

Also, on Mac OS X 10.6 and below, the `GLFW_CONTEXT_VERSION_MAJOR` and `GLFW_CONTEXT_VERSION_MINOR` hints will fail if given a version above 2.1, setting the `GLFW_OPENGL_PROFILE` or `GLFW_OPENGL_FORWARD_COMPAT` hints to a non-default value will cause glfwCreateWindow to fail and the `GLFW_OPENGL_DEBUG_CONTEXT` hint is ignored.

# 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 `VK_MVK_macos_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.