Use Xlib to read resources (#142)

src/main.c

@@ -7,7 +7,10 @@
   #include <windows.h>
 #elif __linux__
   #include <unistd.h>
-  #include "xrdb_parse.h"
+  #include <SDL_syswm.h>
+  #include <X11/Xlib.h>
+  #include <X11/Xatom.h>
+  #include <X11/Xresource.h>
 #elif __APPLE__
   #include <mach-o/dyld.h>
 #endif
@@ -16,16 +19,32 @@
 SDL_Window *window;
 
 static double get_scale(void) {
-#if _WIN32
+#ifdef _WIN32
   float dpi;
   SDL_GetDisplayDPI(0, NULL, &dpi, NULL);
   return dpi / 96.0;
-#elif __unix__
-  int xft_dpi = xrdb_find_dpi();
-  if (xft_dpi > 0) {
-    return xft_dpi / 96.0;
-  }
-  return 1.0;
+#elif __linux__
+  SDL_SysWMinfo info;
+  XrmDatabase db;
+  XrmValue value;
+  char *type = NULL;
+
+  SDL_VERSION(&info.version);
+  if (!SDL_GetWindowWMInfo(window, &info)
+      || info.subsystem != SDL_SYSWM_X11)
+    return 1.0;
+
+  char *resource = XResourceManagerString(info.info.x11.display);
+  if (resource == NULL)
+    return 1.0;
+  
+  XrmInitialize();
+  db = XrmGetStringDatabase(resource);
+  if (XrmGetResource(db, "Xft.dpi", "String", &type, &value) == False
+      || value.addr == NULL)
+    return 1.0;
+
+  return atof(value.addr) / 96.0;
 #else
   return 1.0;
 #endif