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WinRT: removed SDL_HINT_WINRT_PREF_PATH_ROOT (introduced post-2.0.3 &…
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… pre-2.0.4)

A WinRT app's Roaming folder-path can still be retrieved via calls to
SDL_WinRTGetFSPathUTF8() or SDL_WinRTGetFSPathUNICODE(), if need be.
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@DavidLudwig
DavidLudwig committed Dec 3, 2014
1 parent 52760dc commit 5fee84f
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84 changes: 30 additions & 54 deletions docs/README-winrt.md
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Expand Up @@ -116,67 +116,43 @@ Here is a rough list of what works, and what doens't:



Caveats
-------

#### SDL_GetPrefPath() usage when upgrading existing WinRT apps to SDL 2.0.4

SDL 2.0.4 fixes two bugs found in SDL_GetPrefPath() which can affect
an app's save data. These bugs only apply to WinRT apps (and not
Windows Desktop / Win32 apps, or to apps on any other SDL platform).
In particular, for older versions of SDL (anything before 2.0.4):

1. SDL_GetPrefPath() would return an invalid path, one in which attempts
to write files to would fail, in many cases. Some of the path elements
returned by SDL_GetPrefPath() would not get created (as done on other
SDL platforms). Files could be written to this path, however apps would
need to explicitly create the missing directories first.

2. SDL_GetPrefPath() would return a path inside a WinRT 'Roaming' folder,
the contents of which could get automatically synchronized across multiple
devices, by Windows. This process could occur while an app was running.
Apps which were not explicitly built to handle this scenario could
have their SDL_GetPrefPath-backed save data swapped out by Windows at
unexpected times, which raised potential for data-loss (if apps weren't
designed to support live file-synchronization.)
Upgrade Notes
-------------

#### SDL_GetPrefPath() usage when upgrading WinRT apps from SDL 2.0.3

SDL 2.0.4 fixes two bugs found in the WinRT version of SDL_GetPrefPath().
The fixes may affect older, SDL 2.0.3-based apps' save data. Please note
that these changes only apply to SDL-based WinRT apps, and not to apps for
any other platform.

1. SDL_GetPrefPath() would return an invalid path, one in which the path's
directory had not been created. Attempts to create files there
(via fopen(), for example), would fail, unless that directory was
explicitly created beforehand.

2. SDL_GetPrefPath(), for non-WinPhone-based apps, would return a path inside
a WinRT 'Roaming' folder, the contents of which get automatically
synchronized across multiple devices. This process can occur while an
application runs, and can cause existing save-data to be overwritten
at unexpected times, with data from other devices. (Windows Phone apps
written with SDL 2.0.3 did not utilize a Roaming folder, due to API
restrictions in Windows Phone 8.0).


SDL_GetPrefPath(), starting with SDL 2.0.4, addresses these by:

1. making sure that SDL_GetPrefPath() returns a directory in which data
can be written to immediately, without first needing to create directories.

2. basing SDL_GetPrefPath() off of a non-Roaming / 'Local' folder, the
contents of which do not get automatically synchronized across devices,
and which may be safer in terms of data-integrity.

Apps can, at their discretion, choose to utilize WinRT's Roaming
functionality by calling the following before calling SDL_GetPrefPath():

SDL_SetHint(SDL_HINT_WINRT_PREF_PATH_ROOT, "roaming");

Alternatively, to restore SDL_GetPrefPath()'s old behavior (found in
SDL 2.0.3, and in many pre-2.0.4 versions of SDL found on hg.libsdl.org),
whereby a Roaming path is returned for Windows Store apps, and a Local
folder is returned for Windows Phone apps, use the following code:

SDL_SetHint(SDL_HINT_WINRT_PREF_PATH_ROOT, "old");

Before using Roaming data in any capacity, it is highly recommended that
one read the following:

1. Microsoft's documentation on the Roaming data. Details on this can be
found on MSDN, at:
[Guidelines for roaming app data](http://msdn.microsoft.com/en-us/library/windows/apps/hh465094.aspx).

2. the SDL documentation for SDL_HINT_WINRT_PREF_PATH_ROOT, which is
listed inside SDL_hints.h.

Please note that Roaming support is not available on Windows Phone 8.0,
due to limitations in the OS itself. Attempts to use it will fail, with
SDL_GetPrefPath() returning NULL (if SDL_HINT_WINRT_PREF_PATH_ROOT is
set to "roaming" on that platform). Windows Phone 8.1 does not have this
limitation, and does support Roaming data.
2. basing SDL_GetPrefPath() off of a different, non-Roaming folder, the
contents of which do not automatically get synchronized across devices
(and which require less work to use safely, in terms of data integrity).

Apps that wish to get their Roaming folder's path can do so either by using
SDL_WinRTGetFSPathUTF8(), SDL_WinRTGetFSPathUNICODE() (which returns a
UCS-2/wide-char string), or directly through the WinRT class,
Windows.Storage.ApplicationData.



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30 changes: 0 additions & 30 deletions include/SDL_hints.h
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Expand Up @@ -491,36 +491,6 @@ extern "C" {
*/
#define SDL_HINT_WINRT_HANDLE_BACK_BUTTON "SDL_WINRT_HANDLE_BACK_BUTTON"

/**
* \brief A variable that dictates what SDL_GetPrefPath() returns in WinRT apps.
*
* The variable can be set to the following values:
* * "local" - Use the app's 'local' folder to store data.
* * "roaming" - Use the app's 'roaming' folder to store data.
* On Windows Phone 8.0, this setting is not supported due to
* limitations in the OS itself. Attempts to use this (via
* SDL_GetPrefPath()) on Windows Phone 8.0 will fail, with
* SDL_GetPrefPath() returning NULL. (Windows Phone 8.1 does,
* however, support roaming folders.)
* * "old" - Use the app's 'local' folder on Windows Phone, and 'roaming'
* on non-Phone versions of WinRT. This mimics behavior found
* in SDL 2.0.3's implementation of SDL_GetPrefPath() for WinRT
* (and was changed for SDL 2.0.4, further details of which are
* in the "Caveats" section of SDL's
* [WinRT README file](README-winrt.md).
*
* The default is to use the app's "local" folder.
*
* Details on 'local' verses 'roaming' folders can be found on MSDN, in
* the documentation for WinRT's Windows.Storage.ApplicationData class,
* (available at http://msdn.microsoft.com/en-us/library/windows/apps/windows.storage.applicationdata ).
*
* The application's local and roaming paths may, alternatively, be retrieved
* via the SDL_WinRTGetFSPathUTF8() and SDL_WinRTGetFSPathUNICODE() functions,
* which are defined in SDL_system.h.
*/
#define SDL_HINT_WINRT_PREF_PATH_ROOT "SDL_WINRT_PREF_PATH_ROOT"

/**
* \brief A variable that dictates policy for fullscreen Spaces on Mac OS X.
*
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45 changes: 1 addition & 44 deletions src/filesystem/winrt/SDL_sysfilesystem.cpp
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Expand Up @@ -144,49 +144,6 @@ SDL_GetPrefPath(const char *org, const char *app)
* without violating Microsoft's app-store requirements.
*/

/* Default to using a Local/non-Roaming path. WinRT will often attempt
* to synchronize files in Roaming paths, and will do so while an app is
* running. Using a Local path prevents the possibility that an app's
* save-data files will get changed from underneath it, without it
* being ready.
*
* This behavior can be changed via use of the
* SDL_HINT_WINRT_PREF_PATH_ROOT hint.
*/
SDL_WinRT_Path pathType = SDL_WINRT_PATH_LOCAL_FOLDER;

const char * hint = SDL_GetHint(SDL_HINT_WINRT_PREF_PATH_ROOT);
if (hint) {
if (SDL_strcasecmp(hint, "local") == 0) {
pathType = SDL_WINRT_PATH_LOCAL_FOLDER;
} else if (SDL_strcasecmp(hint, "roaming") == 0) {
#if (WINAPI_FAMILY != WINAPI_FAMILY_PHONE_APP) || (NTDDI_VERSION > NTDDI_WIN8)
pathType = SDL_WINRT_PATH_ROAMING_FOLDER;
#else
/* Don't apply a 'Roaming' path on Windows Phone 8.0. Roaming
* data is not supported by that version of the operating system.
*/
SDL_SetError("A Roaming path was specified via SDL_HINT_WINRT_PREF_PATH_ROOT, but Roaming is not supported on Windows Phone 8.0");
return NULL;
#endif
} else if (SDL_strcasecmp(hint, "old") == 0) {
/* Older versions of SDL/WinRT, including 2.0.3, would return a
* pref-path that used a Roaming folder on non-Phone versions of
* Windows, such as Windows 8.0 and Windows 8.1. This has since
* been reverted to using a Local folder, in order to prevent
* problems arising from WinRT automatically synchronizing files
* during an app's lifetime. In case this functionality is
* desired, setting SDL_HINT_WINRT_PREF_PATH_ROOT to "old" will
* trigger the older behavior.
*/
#if WINAPI_FAMILY == WINAPI_FAMILY_PHONE_APP
pathType = SDL_WINRT_PATH_LOCAL_FOLDER;
#else
pathType = SDL_WINRT_PATH_ROAMING_FOLDER;
#endif
}
}

const WCHAR * srcPath = NULL;
WCHAR path[MAX_PATH];
char *retval = NULL;
Expand All @@ -195,7 +152,7 @@ SDL_GetPrefPath(const char *org, const char *app)
size_t new_wpath_len = 0;
BOOL api_result = FALSE;

srcPath = SDL_WinRTGetFSPathUNICODE(pathType);
srcPath = SDL_WinRTGetFSPathUNICODE(SDL_WINRT_PATH_LOCAL_FOLDER);
if ( ! srcPath) {
SDL_SetError("Unable to find a source path");
return NULL;
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