File dialog improvements

- Add a globally-accessible function to handle the parsing of filter extensions
- Remove the ability of putting the wildcard ('*') among other patterns; it's either a list of patterns or a single '*' now
- Add a hint to select between portals and Zenity on Unix

src/dialog/SDL_dialog_utils.h

@@ -0,0 +1,57 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+/* The following are utility functions to help implementations.
+   They are ordered by scope largeness, decreasing. All implementations
+   should use them, as they check for invalid filters. Where they are unused,
+   the validate_* function further down below should be used. */
+
+/* Transform the name given in argument into something viable for the engine.
+   Useful if there are special characters to avoid on certain platforms (such
+   as "|" with Zenity). */
+typedef char *(NameTransform)(const char * name);
+
+/* Converts all the filters into a single string. */
+/* <prefix>[filter]{<separator>[filter]...}<suffix> */
+char *convert_filters(const SDL_DialogFileFilter *filters, NameTransform ntf,
+                      const char *prefix, const char *separator,
+                      const char *suffix, const char *filt_prefix,
+                      const char *filt_separator, const char *filt_suffix,
+                      const char *ext_prefix, const char *ext_separator,
+                      const char *ext_suffix);
+
+/* Converts one filter into a single string. */
+/* <prefix>[filter name]<separator>[filter extension list]<suffix> */
+char *convert_filter(const SDL_DialogFileFilter filter, NameTransform ntf,
+                      const char *prefix, const char *separator,
+                      const char *suffix, const char *ext_prefix,
+                      const char *ext_separator, const char *ext_suffix);
+
+/* Converts the extenstion list of a filter into a single string. */
+/* <prefix>[extension]{<separator>[extension]...}<suffix> */
+char *convert_ext_list(const char *list, const char *prefix,
+                       const char *suffix, const char *separator);
+
+/* Must be used if convert_* functions aren't used */
+/* Returns an error message if there's a problem, NULL otherwise */
+const char *validate_filters(const SDL_DialogFileFilter *filters);
+const char *validate_list(const char *list);