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Moving from GLFW 2 to 3

This is a transition guide for moving from GLFW 2 to 3. It describes what has changed or been removed, but does not include new features unless they are required when moving an existing code base onto the new API. For example, use of the new multi-monitor functions are required to create full screen windows with GLFW 3.

# Removed features

## Threading functions

The threading functions have been removed, including the sleep function. They were fairly primitive, under-used, poorly integrated and took time away from the focus of GLFW (i.e. context, input and window). There are better threading libraries available and native threading support is available in both C++11 and C11, both of which are gaining traction.

If you wish to use the C++11 or C11 facilities but your compiler doesn't yet support them, see the TinyThread++ and TinyCThread projects created by the original author of GLFW. These libraries implement a usable subset of the threading APIs in C++11 and C11, and in fact some GLFW 3 test programs use TinyCThread.

However, GLFW 3 has better support for use from multiple threads than GLFW 2 had. Contexts can be made current on and rendered with from secondary threads, and the documentation explicitly states which functions may be used from secondary threads and which may only be used from the main thread, i.e. the thread that calls main.

## Image and texture loading

The image and texture loading functions have been removed. They only supported the Targa image format, making them mostly useful for beginner level examples. To become of sufficiently high quality to warrant keeping them in GLFW 3, they would need not only to support other formats, but also modern extensions to the OpenGL texturing facilities. This would either add a number of external dependencies (libjpeg, libpng, etc.), or force GLFW to ship with inline versions of these libraries.

As there already are libraries doing this, it seems unnecessary both to duplicate this work and to tie this duplicate to GLFW. Projects similar to GLFW, such as freeglut, could also gain from such a library. Also, would be no platform-specific part of such a library, as both OpenGL and stdio are available wherever GLFW is.

## Character actions

The action parameter of the character callback has been removed. This was an artefact of the origin of GLFW, i.e. being developed in English by a Swede. However, many keyboard layouts require more than one key to produce characters with diacritical marks. Even the Swedish keyboard layout requires this for uncommon cases like ü.

Note that this is only the removal of the action parameter of the character callback, not the removal of the character callback itself.

## Mouse wheel position

The `glfwGetMouseWheel` function has been removed. Scroll events do not represent an absolute state, but is instead an interpretation of a relative change in state, like character input. So, like character input, there is no sane 'current state' to return. The mouse wheel callback has been replaced by a scroll callback that receives two-dimensional scroll offsets.

## GLFWCALL macro

The `GLFWCALL` macro, which made callback functions use __stdcall on Windows, has been removed. GLFW is written in C, not Pascal. Removing this macro means there's one less thing for users of GLFW to remember, i.e. the requirement to mark all callback functions with `GLFWCALL`. It also simplifies the creation of DLLs and DLL link libraries, as there's no need to explicitly disable `@n` entry point suffixes.

## Win32 MBCS support

The Win32 port of GLFW 3 will not compile in MBCS mode. However, because the use of the Unicode version of the Win32 API doesn't affect the process as a whole, but only those windows created using it, it's perfectly possible to call MBCS functions from other parts of the same application. Therefore, even if an application using GLFW has MBCS mode code, there's no need for GLFW itself to support it.

## Support for versions of Windows older than XP

All explicit support for version of Windows older than XP has been removed. There is no code that actively prevents GLFW 3 from running on these earlier versions, but it uses Win32 functions that those versions lack.

Windows XP was released in 2001, and by now (2013) it has not only replaced almost all earlier versions of Windows, but is itself rapidly being replaced by Windows 7 and 8. The MSDN library doesn't even provide documentation for version older than Windows 2000, making it difficult to maintain compatibility with these versions even if it was deemed worth the effort.

The Win32 API has also not stood still, and GLFW 3 uses many functions only present on Windows XP or later. Even supporting an OS as new as XP (new from the perspective of GLFW 2, which still supports Windows 95) requires runtime checking for a number of functions that are present only on modern version of Windows.

## Capture of system-wide hotkeys

The ability to disable and capture system-wide hotkeys like Alt+Tab has been removed. Modern applications, whether they're games, scientific visualisations or something else, are nowadays expected to be good desktop citizens and allow these hotkeys to function even when running in full screen mode.

## Window open parameter

The `GLFW_OPENED` window parameter has been removed. As long as the window object is around, the window is "open". To detect when the user attempts to close the window, see glfwWindowShouldClose and the close callback.

## Automatic polling of events

GLFW 3 does not automatically poll for events on glfwSwapBuffers, which means you need to call glfwPollEvents or glfwWaitEvents yourself. Unlike buffer swap, the event processing functions act on all windows at once.

## Automatic termination

GLFW 3 does not register glfwTerminate with `atexit` at initialization. To properly release all resources allocated by GLFW, you should therefore call glfwTerminate yourself before exiting.

## GLU header inclusion

GLFW 3 does not include the GLU header by default and GLU itself has been deprecated, but you can request that the GLFW 3 header includes it by defining `GLFW_INCLUDE_GLU` before the inclusion of the GLFW 3 header.

# Changes to existing features

## Window handles

Because GLFW 3 supports multiple windows, window handle parameters have been added to all window-related GLFW functions and callbacks. The handle of a newly created window is returned by glfwCreateWindow (formerly `glfwOpenWindow`). Window handles are of the `GLFWwindow*` type, i.e. a pointer to an opaque struct.

## Multi-monitor support

GLFW 3 provides support for multiple monitors, adding the `GLFWmonitor*` handle type and a set of related functions. To request a full screen mode window, instead of passing `GLFW_FULLSCREEN` you specify which monitor you wish the window to use. There is glfwGetPrimaryMonitor that provides behaviour similar to that of GLFW 2.

## Window closing

Window closing initiated by the user is now just an event like any other. Unlike GLFW 2, windows and contexts created with GLFW 3 will not disappear from underfoot. Each window now has a close flag, which is set when the user attempts to close it. By default, nothing else happens and the window stays open and visible. It is then up to you to either destroy the window, take some other action or simply ignore the request. You can query the close flag at any time with glfwWindowShouldClose and set it at any time with glfwSetWindowShouldClose.

The close callback no longer returns a value. Instead, it is called after the close flag has been set so it can override its value, if it chooses to, before event processing completes. You may however not call glfwDestroyWindow from the close callback (or any other window related callback).

GLFW itself never clears the close flag, allowing you to set it for other reasons for the window to close as well, for example the user choosing Quit from the main menu.

## Explicit context management

Each GLFW 3 window has its own OpenGL context and only you, the user, can know which context should be current on which thread at any given time. Therefore, GLFW 3 makes no assumptions about when you want a certain context to be current, leaving that decision to you.

This means, among other things, that you need to call glfwMakeContextCurrent after creating a window before you can call any OpenGL functions.

## Key repeat

The `GLFW_KEY_REPEAT` enable has been removed and key repeat is always enabled for both keys and characters. A new key action, `GLFW_REPEAT`, has been added to allow the key callback to distinguish an initial key press from a repeat. Note that glfwGetKey still returns only `GLFW_PRESS` or `GLFW_RELEASE`.

## Physical key input

GLFW 3 key tokens map to physical keys, unlike in GLFW 2 where they mapped to the values generated by the current keyboard layout. The tokens are named according to the values they would have using the standard US layout, but this is only a convenience, as most programmers are assumed to know that layout. This means that (for example) `GLFW_KEY_LEFT_BRACKET` is always a single key and is the same key in the same place regardless of what keyboard layouts the users of your program has.

The key input facility was never meant for text input, although using it that way worked slightly better in GLFW 2. If you were using it to input text, you should be using the character callback instead, on both GLFW 2 and 3. This will give you the characters being input, as opposed to the keys being pressed.

GLFW 3 has key tokens for all keys on a standard 105 key keyboard, so instead of having to remember whether to check for `'a'` or `'A'`, you now check for `GLFW_KEY_A`.

## Joystick input

The `glfwGetJoystickPos` function has been renamed to glfwGetJoystickAxes.

The `glfwGetJoystickParam` function and the `GLFW_PRESENT`, `GLFW_AXES` and `GLFW_BUTTONS` tokens have been replaced by the glfwJoystickPresent function as well as axis and button counts returned by the glfwGetJoystickAxes and glfwGetJoystickButtons functions.

## Video mode enumeration

Video mode enumeration is now per-monitor. The glfwGetVideoModes function now returns all available modes for a specific monitor instead of requiring you to guess how large an array you need. The `glfwGetDesktopMode` function, which had poorly defined behavior, has been replaced by glfwGetVideoMode, which returns the current mode of a monitor.

## Cursor positioning

GLFW 3 only allows you to position the cursor within a window using glfwSetCursorPos (formerly `glfwSetMousePos`) when that window is active. Unless the window is active, the function fails silently.

## Persistent window hints

Window hints are no longer reset to their default values on window creation, but instead retain their values until modified by glfwWindowHint (formerly `glfwOpenWindowHint`) or glfwDefaultWindowHints, or until the library is terminated and re-initialized.

# Name changes

## Library and header file

The GLFW 3 header is named glfw3.h and moved to the `GLFW` directory, to avoid collisions with the headers of other major versions. Similarly, the GLFW 3 library is named `glfw3,` except when it's installed as a shared library on Unix-like systems, where it uses the soname `libglfw.so.3`.

## Functions

GLFW 2 | GLFW 3 | Notes
--- | --- | ---
`glfwOpenWindow` | glfwCreateWindow | All channel bit depths are now hints
`glfwCloseWindow` | glfwDestroyWindow |
`glfwOpenWindowHint` | glfwWindowHint | Now accepts all `GLFW_*_BITS` tokens
`glfwEnable` | glfwSetInputMode |
`glfwDisable` | glfwSetInputMode |
`glfwGetMousePos` | glfwGetCursorPos |
`glfwSetMousePos` | glfwSetCursorPos |
`glfwSetMousePosCallback` | glfwSetCursorPosCallback |
`glfwSetMouseWheelCallback` | glfwSetScrollCallback | Accepts two-dimensional scroll offsets as doubles
`glfwGetJoystickPos` | glfwGetJoystickAxes |
`glfwGetWindowParam` | glfwGetWindowAttrib |
`glfwGetGLVersion` | glfwGetWindowAttrib | Use `GLFW_CONTEXT_VERSION_MAJOR`, `GLFW_CONTEXT_VERSION_MINOR` and `GLFW_CONTEXT_REVISION`
`glfwGetDesktopMode` | glfwGetVideoMode | Returns the current mode of a monitor
`glfwGetJoystickParam` | glfwJoystickPresent | The axis and button counts are provided by glfwGetJoystickAxes and glfwGetJoystickButtons

## Tokens

GLFW 2 | GLFW 3 | Notes
--- | --- | ---
`GLFW_OPENGL_VERSION_MAJOR` | `GLFW_CONTEXT_VERSION_MAJOR` | Renamed as it applies to OpenGL ES as well
`GLFW_OPENGL_VERSION_MINOR` | `GLFW_CONTEXT_VERSION_MINOR` | Renamed as it applies to OpenGL ES as well
`GLFW_FSAA_SAMPLES` | `GLFW_SAMPLES` | Renamed to match the OpenGL API
`GLFW_ACTIVE` | `GLFW_FOCUSED` | Renamed to match the window focus callback
`GLFW_WINDOW_NO_RESIZE` | `GLFW_RESIZABLE` | The default has been inverted
`GLFW_MOUSE_CURSOR` | `GLFW_CURSOR` | Used with glfwSetInputMode
`GLFW_KEY_ESC` | `GLFW_KEY_ESCAPE` |
`GLFW_KEY_DEL` | `GLFW_KEY_DELETE` |
`GLFW_KEY_PAGEUP` | `GLFW_KEY_PAGE_UP` |
`GLFW_KEY_PAGEDOWN` | `GLFW_KEY_PAGE_DOWN` |
`GLFW_KEY_KP_NUM_LOCK` | `GLFW_KEY_NUM_LOCK` |
`GLFW_KEY_LCTRL` | `GLFW_KEY_LEFT_CONTROL` |
`GLFW_KEY_LSHIFT` | `GLFW_KEY_LEFT_SHIFT` |
`GLFW_KEY_LALT` | `GLFW_KEY_LEFT_ALT` |
`GLFW_KEY_LSUPER` | `GLFW_KEY_LEFT_SUPER` |
`GLFW_KEY_RCTRL` | `GLFW_KEY_RIGHT_CONTROL` |
`GLFW_KEY_RSHIFT` | `GLFW_KEY_RIGHT_SHIFT` |
`GLFW_KEY_RALT` | `GLFW_KEY_RIGHT_ALT` |
`GLFW_KEY_RSUPER` | `GLFW_KEY_RIGHT_SUPER` |