add back winrt hints

Author: 3UR

include/SDL3/SDL_hints.h

@@ -4376,6 +4376,106 @@ extern "C" {
  */
 #define SDL_HINT_WINDOWS_ERASE_BACKGROUND_MODE "SDL_WINDOWS_ERASE_BACKGROUND_MODE"
 
+/** \brief Allows back-button-press events on Windows Phone to be marked as handled
+ *
+ *  Windows Phone devices typically feature a Back button.  When pressed,
+ *  the OS will emit back-button-press events, which apps are expected to
+ *  handle in an appropriate manner.  If apps do not explicitly mark these
+ *  events as 'Handled', then the OS will invoke its default behavior for
+ *  unhandled back-button-press events, which on Windows Phone 8 and 8.1 is to
+ *  terminate the app (and attempt to switch to the previous app, or to the
+ *  device's home screen).
+ *
+ *  Setting the SDL_HINT_WINRT_HANDLE_BACK_BUTTON hint to "1" will cause SDL
+ *  to mark back-button-press events as Handled, if and when one is sent to
+ *  the app.
+ *
+ *  Internally, Windows Phone sends back button events as parameters to
+ *  special back-button-press callback functions.  Apps that need to respond
+ *  to back-button-press events are expected to register one or more
+ *  callback functions for such, shortly after being launched (during the
+ *  app's initialization phase).  After the back button is pressed, the OS
+ *  will invoke these callbacks.  If the app's callback(s) do not explicitly
+ *  mark the event as handled by the time they return, or if the app never
+ *  registers one of these callback, the OS will consider the event
+ *  un-handled, and it will apply its default back button behavior (terminate
+ *  the app).
+ *
+ *  SDL registers its own back-button-press callback with the Windows Phone
+ *  OS.  This callback will emit a pair of SDL key-press events (SDL_KEYDOWN
+ *  and SDL_KEYUP), each with a scancode of SDL_SCANCODE_AC_BACK, after which
+ *  it will check the contents of the hint, SDL_HINT_WINRT_HANDLE_BACK_BUTTON.
+ *  If the hint's value is set to "1", the back button event's Handled
+ *  property will get set to 'true'.  If the hint's value is set to something
+ *  else, or if it is unset, SDL will leave the event's Handled property
+ *  alone.  (By default, the OS sets this property to 'false', to note.)
+ *
+ *  SDL apps can either set SDL_HINT_WINRT_HANDLE_BACK_BUTTON well before a
+ *  back button is pressed, or can set it in direct-response to a back button
+ *  being pressed.
+ *
+ *  In order to get notified when a back button is pressed, SDL apps should
+ *  register a callback function with SDL_AddEventWatch(), and have it listen
+ *  for SDL_KEYDOWN events that have a scancode of SDL_SCANCODE_AC_BACK.
+ *  (Alternatively, SDL_KEYUP events can be listened-for.  Listening for
+ *  either event type is suitable.)  Any value of SDL_HINT_WINRT_HANDLE_BACK_BUTTON
+ *  set by such a callback, will be applied to the OS' current
+ *  back-button-press event.
+ *
+ *  More details on back button behavior in Windows Phone apps can be found
+ *  at the following page, on Microsoft's developer site:
+ *  http://msdn.microsoft.com/en-us/library/windowsphone/develop/jj247550(v=vs.105).aspx
+ */
+#define SDL_HINT_WINRT_HANDLE_BACK_BUTTON "SDL_WINRT_HANDLE_BACK_BUTTON"
+
+/** \brief Label text for a WinRT app's privacy policy link
+ *
+ *  Network-enabled WinRT apps must include a privacy policy.  On Windows 8, 8.1, and RT,
+ *  Microsoft mandates that this policy be available via the Windows Settings charm.
+ *  SDL provides code to add a link there, with its label text being set via the
+ *  optional hint, SDL_HINT_WINRT_PRIVACY_POLICY_LABEL.
+ *
+ *  Please note that a privacy policy's contents are not set via this hint.  A separate
+ *  hint, SDL_HINT_WINRT_PRIVACY_POLICY_URL, is used to link to the actual text of the
+ *  policy.
+ *
+ *  The contents of this hint should be encoded as a UTF8 string.
+ *
+ *  The default value is "Privacy Policy".  This hint should only be set during app
+ *  initialization, preferably before any calls to SDL_Init().
+ *
+ *  For additional information on linking to a privacy policy, see the documentation for
+ *  SDL_HINT_WINRT_PRIVACY_POLICY_URL.
+ */
+#define SDL_HINT_WINRT_PRIVACY_POLICY_LABEL "SDL_WINRT_PRIVACY_POLICY_LABEL"
+
+/**
+ *  \brief A URL to a WinRT app's privacy policy
+ *
+ *  All network-enabled WinRT apps must make a privacy policy available to its
+ *  users.  On Windows 8, 8.1, and RT, Microsoft mandates that this policy be
+ *  be available in the Windows Settings charm, as accessed from within the app.
+ *  SDL provides code to add a URL-based link there, which can point to the app's
+ *  privacy policy.
+ *
+ *  To setup a URL to an app's privacy policy, set SDL_HINT_WINRT_PRIVACY_POLICY_URL
+ *  before calling any SDL_Init() functions.  The contents of the hint should
+ *  be a valid URL.  For example, "http://www.example.com".
+ *
+ *  The default value is "", which will prevent SDL from adding a privacy policy
+ *  link to the Settings charm.  This hint should only be set during app init.
+ *
+ *  The label text of an app's "Privacy Policy" link may be customized via another
+ *  hint, SDL_HINT_WINRT_PRIVACY_POLICY_LABEL.
+ *
+ *  Please note that on Windows Phone, Microsoft does not provide standard UI
+ *  for displaying a privacy policy link, and as such, SDL_HINT_WINRT_PRIVACY_POLICY_URL
+ *  will not get used on that platform.  Network-enabled phone apps should display
+ *  their privacy policy through some other, in-app means.
+ */
+#define SDL_HINT_WINRT_PRIVACY_POLICY_URL "SDL_WINRT_PRIVACY_POLICY_URL"
+
+
 /**
  * A variable controlling whether back-button-press events on Windows Phone to
  * be marked as handled.