mkdir exportdir's parent, if necessary

Tux Paint's export features will fail if the parent
of the export directory didn't exist.  e.g., using the
default (either via XDG or hard-coded fallback) of
"~/Pictures/TuxPaint/", Tux Paint could not export if
"~/Pictures/" didn't exist yet.  It will now try to
mkdir it as well.  h/t Tim Dickson

Updated OPTIONS documents to explain this.

Also, documenting --exportdir in manpage (was missing!)

src/get_fname.c

@@ -1,7 +1,7 @@
 /*
   get_fname.c
 
-  Copyright (c) 2009 - 2020
+  Copyright (c) 2009 - 2021
   http://www.tuxpaint.org/
 
   This program is free software; you can redistribute it and/or modify
@@ -57,6 +57,11 @@
     and easily-accessible place for end users to retrieve the exports.
 
     The defaults may be overridden with the "--exportdir" option.
+
+  * DIR_EXPORT_PARENT: The parent of the directory
+    specified by DIR_EXPORT.  (e.g., if /home/username/Pictures/TuxPaint/
+    is our export dir., we may need to make .../Pictures first,
+    the first time we export something.)
 */
 
 
@@ -88,7 +93,7 @@ char *get_fname(const char *const name, int kind)
     dir = savedir;
   } else if (kind == DIR_DATA) {
     dir = datadir;
-  } else if (kind == DIR_EXPORT) {
+  } else if (kind == DIR_EXPORT || kind == DIR_EXPORT_PARENT) {
     dir = exportdir;
   }
 
@@ -97,6 +102,20 @@ char *get_fname(const char *const name, int kind)
 	   dir, (*name) ? '/' : '\0', /* Some mkdir()'s don't like trailing slashes */
 	   name);
 
+  if (kind == DIR_EXPORT_PARENT) {
+    int len, i, stop;
+
+    stop = -1;
+    len = strlen(f);
+    for (i = len - 1; i >= 0 && stop == -1; i--) {
+      if (f[i] == '/')
+        stop = i;
+    }
+    if (stop != -1) {
+      f[stop] = '\0';
+    }
+  }
+
   return strdup(f);
 }
 

src/get_fname.h

@@ -1,7 +1,7 @@
 /*
   get_fname.h
 
-  Copyright (c) 2009 - July 25, 2020
+  Copyright (c) 2009 - January 13, 2021
   http://www.tuxpaint.org/
 
   This program is free software; you can redistribute it and/or modify
@@ -34,7 +34,8 @@ enum
   /* (See get_fname.c for details) */
   DIR_SAVE,
   DIR_DATA,
-  DIR_EXPORT
+  DIR_EXPORT,
+  DIR_EXPORT_PARENT
 };
 
 char *get_fname(const char *const name, int kind);

src/manpage/tuxpaint.1

@@ -1,5 +1,5 @@
-.\" tuxpaint.1 - 2020.12.27
-.TH TUXPAINT 1 "27 December 2020" "0.9.26" "Tux Paint"
+.\" tuxpaint.1 - 2021.01.13
+.TH TUXPAINT 1 "13 January 2021" "0.9.26" "Tux Paint"
 .SH NAME
 tuxpaint -- "Tux Paint", a drawing program for young children.
 
@@ -131,6 +131,8 @@ tuxpaint -- "Tux Paint", a drawing program for young children.
 .br
 [\-\-savedir \fIDIR\fP]
 .br
+[\-\-exportdir \fIDIR\fP]
+.br
 [\-\-datadir \fIDIR\fP]
 .br
 [\-\-saveover]
@@ -484,7 +486,11 @@ Use the \fIalllocalefonts\fP option to load all such fonts, for use in the
 
 .TP 8
 .B \-\-savedir \fIDIR\fP
-Specify where \fITux Paint\fP should save files.
+Specify where \fITux Paint\fP should save and load its drawings.
+
+.TP 8
+.B \-\-exportdir \fIDIR\fP
+Specify where \fITux Paint\fP should export drawings and animations.
 
 .TP 8
 .B \-\-datadir \fIDIR\fP

src/tuxpaint.c

@@ -25963,9 +25963,16 @@ static char * get_export_filepath(const char * ext) {
 
 
   /* Make sure the export dir exists */
-  if (!make_directory(DIR_EXPORT, "", "Can't create export directory (E016)"))
+  if (!make_directory(DIR_EXPORT, "", "Can't create export directory; will try to make its parent (E016)"))
     {
-      return NULL;
+      /* See if perhaps we need to try and make its parent directory first? */
+      if (make_directory(DIR_EXPORT_PARENT, "", "Can't create export directory parent (E016b)")) {
+        if (!make_directory(DIR_EXPORT, "", "Can't create export directory (E016c)")) {
+          return NULL;
+        }
+      } else {
+        return NULL;
+      }
     }
 
   /* Create a unique filename, within that dir */