rewrite D_DoomExeDir() to use SDL_GetBasePath() (#1145)

* rewrite D_DoomExeDir() to use SDL_GetBasePath()

* move D_DoomExeDir() to src/d_iwad.c

src/d_iwad.c

@@ -18,6 +18,8 @@
 
 #include <stdlib.h>
 
+#include "SDL_filesystem.h" // [FG] SDL_GetBasePath()
+
 #include "i_system.h"
 #include "m_io.h"
 #include "d_iwad.h"
@@ -61,6 +63,32 @@ static void AddIWADDir(char *dir)
     }
 }
 
+// Return the path where the executable lies -- Lee Killough
+
+char *D_DoomExeDir(void)
+{
+    static char *base;
+
+    if (base == NULL) // cache multiple requests
+    {
+        char *result;
+
+        result = SDL_GetBasePath();
+        if (result != NULL)
+        {
+            base = M_StringDuplicate(result);
+            SDL_free(result);
+        }
+        else
+        {
+            result = M_DirName(myargv[0]);
+            base = M_StringDuplicate(result);
+        }
+    }
+
+    return base;
+}
+
 // This is Windows-specific code that automatically finds the location
 // of installed IWAD files.  The registry is inspected to find special
 // keys installed by the Windows installers for various CD versions
@@ -538,7 +566,7 @@ void BuildIWADDirList(void)
 
     // Next check the directory where the executable is located. This might
     // be different from the current directory.
-    AddIWADDir(M_DirName(myargv[0]));
+    AddIWADDir(D_DoomExeDir());
 
     // Add DOOMWADDIR if it is in the environment
     env = M_getenv("DOOMWADDIR");

src/d_iwad.h

@@ -29,6 +29,7 @@ typedef struct
     const char *description;
 } iwad_t;
 
+char *D_DoomExeDir(void);       // killough 2/16/98: path to executable's dir
 char *D_FindWADByName(const char *filename);
 char *D_TryFindWADByName(const char *filename);
 char *D_FindIWADFile(GameMode_t *mode, GameMission_t *mission);

src/d_main.c

@@ -658,19 +658,6 @@ void D_AddFile(const char *file)
   wadfiles[numwadfiles] = NULL;
 }
 
-// Return the path where the executable lies -- Lee Killough
-char *D_DoomExeDir(void)
-{
-  static char *base;
-
-  if (!base) // cache multiple requests
-  {
-    base = M_DirName(myargv[0]);
-  }
-
-  return base;
-}
-
 // killough 10/98: return the name of the program the exe was invoked as
 char *D_DoomExeName(void)
 {

src/d_main.h

@@ -28,7 +28,6 @@ extern char **wadfiles;       // killough 11/98
 
 void D_AddFile(const char *file);
 
-char *D_DoomExeDir(void);       // killough 2/16/98: path to executable's dir
 char *D_DoomExeName(void);      // killough 10/98: executable's name
 extern char *basesavegame;     // killough 2/16/98: savegame path
 extern char *screenshotdir; // [FG] screenshot path