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+/*!
+
+@page input_guide Input guide
+ 
+@tableofcontents
+
+This guide introduces the input related functions of GLFW.  For details on
+a specific function in this category, see the @ref input.  There are also guides
+for the other areas of GLFW.
+
+ - @ref intro_guide
+ - @ref window_guide
+ - @ref context_guide
+ - @ref vulkan_guide
+ - @ref monitor_guide
+
+GLFW provides many kinds of input.  While some can only be polled, like time, or
+only received via callbacks, like scrolling, there are those that provide both
+callbacks and polling.  Where a callback is provided, that is the recommended
+way to receive that kind of input.  The more you can use callbacks the less time
+your users' machines will need to spend polling.
+
+All input callbacks receive a window handle.  By using the
+[window user pointer](@ref window_userptr), you can access non-global structures
+or objects from your callbacks.
+
+To get a better feel for how the various events callbacks behave, run the
+`events` test program.  It register every callback supported by GLFW and prints
+out all arguments provided for every event, along with time and sequence
+information.
+
+
+@section events Event processing
+
+GLFW needs to communicate regularly with the window system both in order to
+receive events and to show that the application hasn't locked up.  Event
+processing must be done regularly while you have any windows and is normally
+done each frame after [buffer swapping](@ref buffer_swap).  Even when you have
+no windows, event polling needs to be done in order to receive monitor
+connection events.
+
+There are two functions for processing pending events.  @ref glfwPollEvents,
+processes only those events that have already been received and then returns
+immediately.
+
+@code
+glfwPollEvents();
+@endcode
+
+This is the best choice when rendering continually, like most games do.
+
+If you only need to update the contents of the window when you receive new
+input, @ref glfwWaitEvents is a better choice.
+
+@code
+glfwWaitEvents();
+@endcode
+
+It puts the thread to sleep until at least one event has been received and then
+processes all received events.  This saves a great deal of CPU cycles and is
+useful for, for example, editing tools.  There must be at least one GLFW window
+for this function to sleep.
+
+If you want to wait for events but have UI elements that need periodic updates,
+call @ref glfwWaitEventsTimeout.
+
+@code
+glfwWaitEventsTimeout(0.7);
+@endcode
+
+It puts the thread to sleep until at least one event has been received, or until
+the specified number of seconds have elapsed.  It then processes any received
+events.
+
+If the main thread is sleeping in @ref glfwWaitEvents, you can wake it from
+another thread by posting an empty event to the event queue with @ref
+glfwPostEmptyEvent.
+
+@code
+glfwPostEmptyEvent();
+@endcode
+
+Do not assume that callbacks will _only_ be called through either of the above
+functions.  While it is necessary to process events in the event queue, some
+window systems will send some events directly to the application, which in turn
+causes callbacks to be called outside of regular event processing.
+
+
+@section input_keyboard Keyboard input
+
+GLFW divides keyboard input into two categories; key events and character
+events.  Key events relate to actual physical keyboard keys, whereas character
+events relate to the Unicode code points generated by pressing some of them.
+
+Keys and characters do not map 1:1.  A single key press may produce several
+characters, and a single character may require several keys to produce.  This
+may not be the case on your machine, but your users are likely not all using the
+same keyboard layout, input method or even operating system as you.
+
+
+@subsection input_key Key input
+
+If you wish to be notified when a physical key is pressed or released or when it
+repeats, set a key callback.
+
+@code
+glfwSetKeyCallback(window, key_callback);
+@endcode
+
+The callback function receives the [keyboard key](@ref keys), platform-specific
+scancode, key action and [modifier bits](@ref mods).
+
+@code
+void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
+{
+    if (key == GLFW_KEY_E && action == GLFW_PRESS)
+        activate_airship();
+}
+@endcode
+
+The action is one of `GLFW_PRESS`, `GLFW_REPEAT` or `GLFW_RELEASE`.  The key
+will be `GLFW_KEY_UNKNOWN` if GLFW lacks a key token for it, for example
+_E-mail_ and _Play_ keys.
+
+The scancode is unique for every key, regardless of whether it has a key token.
+Scancodes are platform-specific but consistent over time, so keys will have
+different scancodes depending on the platform but they are safe to save to disk.
+
+Key states for [named keys](@ref keys) are also saved in per-window state arrays
+that can be polled with @ref glfwGetKey.
+
+@code
+int state = glfwGetKey(window, GLFW_KEY_E);
+if (state == GLFW_PRESS)
+    activate_airship();
+@endcode
+
+The returned state is one of `GLFW_PRESS` or `GLFW_RELEASE`.
+
+This function only returns cached key event state.  It does not poll the
+system for the current state of the key.
+
+Whenever you poll state, you risk missing the state change you are looking for.
+If a pressed key is released again before you poll its state, you will have
+missed the key press.  The recommended solution for this is to use a
+key callback, but there is also the `GLFW_STICKY_KEYS` input mode.
+
+@code
+glfwSetInputMode(window, GLFW_STICKY_KEYS, 1);
+@endcode
+
+When sticky keys mode is enabled, the pollable state of a key will remain
+`GLFW_PRESS` until the state of that key is polled with @ref glfwGetKey.  Once
+it has been polled, if a key release event had been processed in the meantime,
+the state will reset to `GLFW_RELEASE`, otherwise it will remain `GLFW_PRESS`.
+
+The `GLFW_KEY_LAST` constant holds the highest value of any
+[named key](@ref keys).
+
+
+@subsection input_char Text input
+
+GLFW supports text input in the form of a stream of
+[Unicode code points](https://en.wikipedia.org/wiki/Unicode), as produced by the
+operating system text input system.  Unlike key input, text input obeys keyboard
+layouts and modifier keys and supports composing characters using
+[dead keys](https://en.wikipedia.org/wiki/Dead_key).  Once received, you can
+encode the code points into
+[UTF-8](https://en.wikipedia.org/wiki/UTF-8) or any other encoding you prefer.
+
+Because an `unsigned int` is 32 bits long on all platforms supported by GLFW,
+you can treat the code point argument as native endian
+[UTF-32](https://en.wikipedia.org/wiki/UTF-32).
+
+There are two callbacks for receiving Unicode code points.  If you wish to
+offer regular text input, set a character callback.
+
+@code
+glfwSetCharCallback(window, character_callback);
+@endcode
+
+The callback function receives Unicode code points for key events that would
+have led to regular text input and generally behaves as a standard text field on
+that platform.
+
+@code
+void character_callback(GLFWwindow* window, unsigned int codepoint)
+{
+}
+@endcode
+
+If you wish to receive even those Unicode code points generated with modifier
+key combinations that a plain text field would ignore, or just want to know
+exactly what modifier keys were used, set a character with modifiers callback.
+
+@code
+glfwSetCharModsCallback(window, charmods_callback);
+@endcode
+
+The callback function receives Unicode code points and
+[modifier bits](@ref mods).
+
+@code
+void charmods_callback(GLFWwindow* window, unsigned int codepoint, int mods)
+{
+}
+@endcode
+
+
+@subsection input_key_name Key names
+
+If you wish to refer to keys by name, you can query the keyboard layout
+dependent name of printable keys with @ref glfwGetKeyName.
+
+@code
+const char* key_name = glfwGetKeyName(GLFW_KEY_W, 0);
+show_tutorial_hint("Press %s to move forward", key_name);
+@endcode
+
+This function can handle both [keys and scancodes](@ref input_key).  If the
+specified key is `GLFW_KEY_UNKNOWN` then the scancode is used, otherwise it is
+ignored.  This matches the behavior of the key callback, meaning the callback
+arguments can always be passed unmodified to this function.
+
+
+@section input_mouse Mouse input
+
+Mouse input comes in many forms, including cursor motion, button presses and
+scrolling offsets.  The cursor appearance can also be changed, either to
+a custom image or a standard cursor shape from the system theme.
+
+
+@subsection cursor_pos Cursor position
+
+If you wish to be notified when the cursor moves over the window, set a cursor
+position callback.
+
+@code
+glfwSetCursorPosCallback(window, cursor_pos_callback);
+@endcode
+
+The callback functions receives the cursor position, measured in screen
+coordinates but relative to the top-left corner of the window client area.  On
+platforms that provide it, the full sub-pixel cursor position is passed on.
+
+@code
+static void cursor_position_callback(GLFWwindow* window, double xpos, double ypos)
+{
+}
+@endcode
+
+The cursor position is also saved per-window and can be polled with @ref
+glfwGetCursorPos.
+
+@code
+double xpos, ypos;
+glfwGetCursorPos(window, &xpos, &ypos);
+@endcode
+
+
+@subsection cursor_mode Cursor modes
+
+The `GLFW_CURSOR` input mode provides several cursor modes for special forms of
+mouse motion input.  By default, the cursor mode is `GLFW_CURSOR_NORMAL`,
+meaning the regular arrow cursor (or another cursor set with @ref glfwSetCursor)
+is used and cursor motion is not limited.
+
+If you wish to implement mouse motion based camera controls or other input
+schemes that require unlimited mouse movement, set the cursor mode to
+`GLFW_CURSOR_DISABLED`.
+
+@code
+glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
+@endcode
+
+This will hide the cursor and lock it to the specified window.  GLFW will then
+take care of all the details of cursor re-centering and offset calculation and
+providing the application with a virtual cursor position.  This virtual position
+is provided normally via both the cursor position callback and through polling.
+
+@note You should not implement your own version of this functionality using
+other features of GLFW.  It is not supported and will not work as robustly as
+`GLFW_CURSOR_DISABLED`.
+
+If you just wish the cursor to become hidden when it is over a window, set
+the cursor mode to `GLFW_CURSOR_HIDDEN`.
+
+@code
+glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_HIDDEN);
+@endcode
+
+This mode puts no limit on the motion of the cursor.
+
+To exit out of either of these special modes, restore the `GLFW_CURSOR_NORMAL`
+cursor mode.
+
+@code
+glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_NORMAL);
+@endcode
+
+
+@subsection cursor_object Cursor objects
+
+GLFW supports creating both custom and system theme cursor images, encapsulated
+as @ref GLFWcursor objects.  They are created with @ref glfwCreateCursor or @ref
+glfwCreateStandardCursor and destroyed with @ref glfwDestroyCursor, or @ref
+glfwTerminate, if any remain.
+
+
+@subsubsection cursor_custom Custom cursor creation
+
+A custom cursor is created with @ref glfwCreateCursor, which returns a handle to
+the created cursor object.  For example, this creates a 16x16 white square
+cursor with the hot-spot in the upper-left corner:
+
+@code
+unsigned char pixels[16 * 16 * 4];
+memset(pixels, 0xff, sizeof(pixels));
+
+GLFWimage image;
+image.width = 16;
+image.height = 16;
+image.pixels = pixels;
+
+GLFWcursor* cursor = glfwCreateCursor(&image, 0, 0);
+@endcode
+
+If cursor creation fails, `NULL` will be returned, so it is necessary to check
+the return value.
+
+The image data is 32-bit, little-endian, non-premultiplied RGBA, i.e. eight bits
+per channel.  The pixels are arranged canonically as sequential rows, starting
+from the top-left corner.
+
+
+@subsubsection cursor_standard Standard cursor creation
+
+A cursor with a [standard shape](@ref shapes) from the current system cursor
+theme can be can be created with @ref glfwCreateStandardCursor.
+
+@code
+GLFWcursor* cursor = glfwCreateStandardCursor(GLFW_HRESIZE_CURSOR);
+@endcode
+
+These cursor objects behave in the exact same way as those created with @ref
+glfwCreateCursor except that the system cursor theme provides the actual image.
+
+
+@subsubsection cursor_destruction Cursor destruction
+
+When a cursor is no longer needed, destroy it with @ref glfwDestroyCursor.
+
+@code
+glfwDestroyCursor(cursor);
+@endcode
+
+Cursor destruction always succeeds.  All cursors remaining when @ref
+glfwTerminate is called are destroyed as well.
+
+
+@subsubsection cursor_set Cursor setting
+
+A cursor can be set as current for a window with @ref glfwSetCursor.
+
+@code
+glfwSetCursor(window, cursor);
+@endcode
+
+Once set, the cursor image will be used as long as the system cursor is over the
+client area of the window and the [cursor mode](@ref cursor_mode) is set
+to `GLFW_CURSOR_NORMAL`.
+
+A single cursor may be set for any number of windows.
+
+To remove a cursor from a window, set the cursor of that window to `NULL`.
+
+@code
+glfwSetCursor(window, NULL);
+@endcode
+
+When a cursor is destroyed, it is removed from any window where it is set.  This
+does not affect the cursor modes of those windows.
+
+
+@subsection cursor_enter Cursor enter/leave events
+
+If you wish to be notified when the cursor enters or leaves the client area of
+a window, set a cursor enter/leave callback.
+
+@code
+glfwSetCursorEnterCallback(window, cursor_enter_callback);
+@endcode
+
+The callback function receives the new classification of the cursor.
+
+@code
+void cursor_enter_callback(GLFWwindow* window, int entered)
+{
+    if (entered)
+    {
+        // The cursor entered the client area of the window
+    }
+    else
+    {
+        // The cursor left the client area of the window
+    }
+}
+@endcode
+
+
+@subsection input_mouse_button Mouse button input
+
+If you wish to be notified when a mouse button is pressed or released, set
+a mouse button callback.
+
+@code
+glfwSetMouseButtonCallback(window, mouse_button_callback);
+@endcode
+
+The callback function receives the [mouse button](@ref buttons), button action
+and [modifier bits](@ref mods).
+
+@code
+void mouse_button_callback(GLFWwindow* window, int button, int action, int mods)
+{
+    if (button == GLFW_MOUSE_BUTTON_RIGHT && action == GLFW_PRESS)
+        popup_menu();
+}
+@endcode
+
+The action is one of `GLFW_PRESS` or `GLFW_RELEASE`.
+
+Mouse button states for [named buttons](@ref buttons) are also saved in
+per-window state arrays that can be polled with @ref glfwGetMouseButton.
+
+@code
+int state = glfwGetMouseButton(window, GLFW_MOUSE_BUTTON_LEFT);
+if (state == GLFW_PRESS)
+    upgrade_cow();
+@endcode
+
+The returned state is one of `GLFW_PRESS` or `GLFW_RELEASE`.
+
+This function only returns cached mouse button event state.  It does not poll
+the system for the current state of the mouse button.
+
+Whenever you poll state, you risk missing the state change you are looking for.
+If a pressed mouse button is released again before you poll its state, you will have
+missed the button press.  The recommended solution for this is to use a
+mouse button callback, but there is also the `GLFW_STICKY_MOUSE_BUTTONS`
+input mode.
+
+@code
+glfwSetInputMode(window, GLFW_STICKY_MOUSE_BUTTONS, 1);
+@endcode
+
+When sticky mouse buttons mode is enabled, the pollable state of a mouse button
+will remain `GLFW_PRESS` until the state of that button is polled with @ref
+glfwGetMouseButton.  Once it has been polled, if a mouse button release event
+had been processed in the meantime, the state will reset to `GLFW_RELEASE`,
+otherwise it will remain `GLFW_PRESS`.
+
+The `GLFW_MOUSE_BUTTON_LAST` constant holds the highest value of any
+[named button](@ref buttons).
+
+
+@subsection scrolling Scroll input
+
+If you wish to be notified when the user scrolls, whether with a mouse wheel or
+touchpad gesture, set a scroll callback.
+
+@code
+glfwSetScrollCallback(window, scroll_callback);
+@endcode
+
+The callback function receives two-dimensional scroll offsets.
+
+@code
+void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
+{
+}
+@endcode
+
+A simple mouse wheel, being vertical, provides offsets along the Y-axis.
+
+
+@section joystick Joystick input
+
+The joystick functions expose connected joysticks and controllers, with both
+referred to as joysticks.  It supports up to sixteen joysticks, ranging from
+`GLFW_JOYSTICK_1`, `GLFW_JOYSTICK_2` up to `GLFW_JOYSTICK_LAST`.  You can test
+whether a [joystick](@ref joysticks) is present with @ref glfwJoystickPresent.
+
+@code
+int present = glfwJoystickPresent(GLFW_JOYSTICK_1);
+@endcode
+
+When GLFW is initialized, detected joysticks are added to to the beginning of
+the array, starting with `GLFW_JOYSTICK_1`.  Once a joystick is detected, it
+keeps its assigned index until it is disconnected, so as joysticks are connected
+and disconnected, they will become spread out.
+
+Joystick state is updated as needed when a joystick function is called and does
+not require a window to be created or @ref glfwPollEvents or @ref glfwWaitEvents
+to be called.
+
+
+@subsection joystick_axis Joystick axis states
+
+The positions of all axes of a joystick are returned by @ref
+glfwGetJoystickAxes.  See the reference documentation for the lifetime of the
+returned array.
+
+@code
+int count;
+const float* axes = glfwGetJoystickAxes(GLFW_JOYSTICK_1, &count);
+@endcode
+
+Each element in the returned array is a value between -1.0 and 1.0.
+
+
+@subsection joystick_button Joystick button states
+
+The states of all buttons of a joystick are returned by @ref
+glfwGetJoystickButtons.  See the reference documentation for the lifetime of the
+returned array.
+
+@code
+int count;
+const unsigned char* axes = glfwGetJoystickButtons(GLFW_JOYSTICK_1, &count);
+@endcode
+
+Each element in the returned array is either `GLFW_PRESS` or `GLFW_RELEASE`.
+
+
+@subsection joystick_name Joystick name
+
+The human-readable, UTF-8 encoded name of a joystick is returned by @ref
+glfwGetJoystickName.  See the reference documentation for the lifetime of the
+returned string.           
+
+@code
+const char* name = glfwGetJoystickName(GLFW_JOYSTICK_1);
+@endcode
+
+Joystick names are not guaranteed to be unique.  Two joysticks of the same model
+and make may have the same name.  Only the [joystick token](@ref joysticks) is
+guaranteed to be unique, and only until that joystick is disconnected.
+
+
+@subsection joystick_event Joystick configuration changes
+
+If you wish to be notified when a joystick is connected or disconnected, set
+a joystick callback.
+
+@code
+glfwSetJoystickCallback(joystick_callback);
+@endcode
+
+The callback function receives the ID of the joystick that has been connected
+and disconnected and the event that occurred.
+
+@code
+void joystick_callback(int joy, int event)
+{
+    if (event == GLFW_CONNECTED)
+    {
+        // The joystick was connected
+    }
+    else if (event == GLFW_DISCONNECTED)
+    {
+        // The joystick was disconnected
+    }
+}
+@endcode
+
+
+@section time Time input
+
+GLFW provides high-resolution time input, in seconds, with @ref glfwGetTime.
+
+@code
+double seconds = glfwGetTime();
+@endcode
+
+It returns the number of seconds since the timer was started when the library
+was initialized with @ref glfwInit.  The platform-specific time sources used
+usually have micro- or nanosecond resolution.
+
+You can modify the reference time with @ref glfwSetTime.
+
+@code
+glfwSetTime(4.0);
+@endcode
+
+This sets the timer to the specified time, in seconds.
+
+You can also access the raw timer value, measured in 1 / frequency
+seconds, with @ref glfwGetTimerValue.
+
+@code
+uint64_t value = glfwGetTimerValue();
+@endcode
+
+The frequency of the raw timer varies depending on what time sources are
+available on the machine.  You can query its frequency, in Hz, with @ref
+glfwGetTimerFrequency.
+
+@code
+uint64_t freqency = glfwGetTimerFrequency();
+@endcode
+
+
+@section clipboard Clipboard input and output
+
+If the system clipboard contains a UTF-8 encoded string or if it can be
+converted to one, you can retrieve it with @ref glfwGetClipboardString.  See the
+reference documentation for the lifetime of the returned string.
+
+@code
+const char* text = glfwGetClipboardString(window);
+if (text)
+    insert_text(text);
+@endcode
+
+If the clipboard is empty or if its contents could not be converted, `NULL` is
+returned.
+
+The contents of the system clipboard can be set to a UTF-8 encoded string with
+@ref glfwSetClipboardString.
+
+@code
+glfwSetClipboardString(window, "A string with words in it");
+@endcode
+
+The clipboard functions take a window handle argument because some window
+systems require a window to communicate with the system clipboard.  Any valid
+window may be used.
+
+
+@section path_drop Path drop input
+
+If you wish to receive the paths of files and/or directories dropped on
+a window, set a file drop callback.
+
+@code
+glfwSetDropCallback(window, drop_callback);
+@endcode
+
+The callback function receives an array of paths encoded as UTF-8.
+
+@code
+void drop_callback(GLFWwindow* window, int count, const char** paths)
+{
+    int i;
+    for (i = 0;  i < count;  i++)
+        handle_dropped_file(paths[i]);
+}
+@endcode
+
+The path array and its strings are only valid until the file drop callback
+returns, as they may have been generated specifically for that event.  You need
+to make a deep copy of the array if you want to keep the paths.
+
+*/