diff --git a/direct/src/plugin/Sources.pp b/direct/src/plugin/Sources.pp
index 1ae6e529b0..1794fcd86a 100644
--- a/direct/src/plugin/Sources.pp
+++ b/direct/src/plugin/Sources.pp
@@ -9,12 +9,6 @@
   #define LIB_PREFIX
 
   #define OTHER_LIBS $[if $[OSX_PLATFORM],subprocbuffer]
-  
-  // We need this because we don't
-  // include dtool_config.h.
-  #if $[HAVE_X11]
-    #define EXTRA_CDEFS HAVE_X11
-  #endif
 
   #define COMBINED_SOURCES \
     $[TARGET]_composite1.cxx
diff --git a/direct/src/plugin/load_plugin.cxx b/direct/src/plugin/load_plugin.cxx
index c5c21fe9dd..ef66137acf 100755
--- a/direct/src/plugin/load_plugin.cxx
+++ b/direct/src/plugin/load_plugin.cxx
@@ -123,8 +123,8 @@ static void unload_dso();
 //               path.
 ////////////////////////////////////////////////////////////////////
 bool
-load_plugin(const string &p3d_plugin_filename, 
-            const string &contents_filename) {
+load_plugin(const string &p3d_plugin_filename, const string &contents_filename,
+            const string &download_url, const string &platform) {
   string filename = p3d_plugin_filename;
   if (filename.empty()) {
     // Look for the plugin along the path.
@@ -293,7 +293,8 @@ load_plugin(const string &p3d_plugin_filename,
   // Successfully loaded.
   plugin_loaded = true;
 
-  if (!P3D_initialize(P3D_API_VERSION, contents_filename.c_str())) {
+  if (!P3D_initialize(P3D_API_VERSION, contents_filename.c_str(),
+                      download_url.c_str(), platform.c_str())) {
     // Oops, failure to initialize.
     cerr << "Failed to initialize plugin (wrong API version?)\n";
     unload_plugin();
diff --git a/direct/src/plugin/load_plugin.h b/direct/src/plugin/load_plugin.h
index 59562f31df..455cbd106c 100755
--- a/direct/src/plugin/load_plugin.h
+++ b/direct/src/plugin/load_plugin.h
@@ -58,8 +58,9 @@ extern P3D_instance_feed_url_stream_func *P3D_instance_feed_url_stream;
 extern P3D_instance_handle_event_func *P3D_instance_handle_event;
 
 string get_plugin_basename();
-bool load_plugin(const string &p3d_plugin_filename,
-                 const string &contents_filename);
+bool 
+load_plugin(const string &p3d_plugin_filename, const string &contents_filename,
+            const string &download_url, const string &platform);
 void unload_plugin();
 bool is_plugin_loaded();
 
diff --git a/direct/src/plugin/p3dInstanceManager.cxx b/direct/src/plugin/p3dInstanceManager.cxx
index df51e23c76..8b4bfb0eb9 100644
--- a/direct/src/plugin/p3dInstanceManager.cxx
+++ b/direct/src/plugin/p3dInstanceManager.cxx
@@ -26,6 +26,10 @@
 #include "fileSpec.h"
 #include "get_tinyxml.h"
 
+// We can include this header file to get the DTOOL_PLATFORM
+// definition, even though we don't link with dtool.
+#include "dtool_platform.h"
+
 #ifdef _WIN32
 #include <shlobj.h>
 #else
@@ -120,14 +124,29 @@ P3DInstanceManager::
 //               redownloaded.
 ////////////////////////////////////////////////////////////////////
 bool P3DInstanceManager::
-initialize(const string &contents_filename) {
+initialize(const string &contents_filename, const string &download_url,
+           const string &platform) {
+
   _root_dir = find_root_dir();
-  _download_url = P3D_PLUGIN_DOWNLOAD;
-  _platform = P3D_PLUGIN_PLATFORM;
+  _download_url = download_url;
+  if (_download_url.empty()) {
+    _download_url = P3D_PLUGIN_DOWNLOAD;
+  }
+  _platform = platform;
+  if (_platform.empty()) {
+    _platform = DTOOL_PLATFORM;
+  }
+
+  // Ensure that the download URL ends with a slash.
+  if (!_download_url.empty() && _download_url[_download_url.size() - 1] != '/') {
+    _download_url += "/";
+  }
 
   nout << "_root_dir = " << _root_dir
+       << ", contents = " << contents_filename
        << ", download = " << _download_url
-       << ", contents = " << contents_filename << "\n";
+       << ", platform = " << _platform
+       << "\n";
 
   if (_root_dir.empty()) {
     nout << "Could not find root directory.\n";
diff --git a/direct/src/plugin/p3dInstanceManager.h b/direct/src/plugin/p3dInstanceManager.h
index f2abc6b55d..03411dea70 100644
--- a/direct/src/plugin/p3dInstanceManager.h
+++ b/direct/src/plugin/p3dInstanceManager.h
@@ -39,7 +39,9 @@ private:
   ~P3DInstanceManager();
 
 public:
-  bool initialize(const string &contents_xml_filename);
+  bool initialize(const string &contents_filename,
+                  const string &download_url,
+                  const string &platform);
 
   inline bool is_initialized() const;
 
diff --git a/direct/src/plugin/p3d_plugin.cxx b/direct/src/plugin/p3d_plugin.cxx
index 94aed438ce..d56f1edbc8 100644
--- a/direct/src/plugin/p3d_plugin.cxx
+++ b/direct/src/plugin/p3d_plugin.cxx
@@ -38,7 +38,8 @@ ostream *nout_stream;
 
 
 bool 
-P3D_initialize(int api_version, const char *contents_filename) {
+P3D_initialize(int api_version, const char *contents_filename,
+               const char *download_url, const char *platform) {
   if (api_version != P3D_API_VERSION) {
     // Can't accept an incompatible version.
     return false;
@@ -54,6 +55,14 @@ P3D_initialize(int api_version, const char *contents_filename) {
     contents_filename = "";
   }
 
+  if (download_url == NULL){ 
+    download_url = "";
+  }
+
+  if (platform == NULL) {
+    platform = "";
+  }
+
 #ifdef P3D_PLUGIN_LOGFILE2
   string logfilename = P3D_PLUGIN_LOGFILE2;
 #else
@@ -83,7 +92,7 @@ P3D_initialize(int api_version, const char *contents_filename) {
   }
 
   P3DInstanceManager *inst_mgr = P3DInstanceManager::get_global_ptr();
-  bool result = inst_mgr->initialize(contents_filename);
+  bool result = inst_mgr->initialize(contents_filename, download_url, platform);
   RELEASE_LOCK(_api_lock);
   return result;
 }
diff --git a/direct/src/plugin/p3d_plugin.h b/direct/src/plugin/p3d_plugin.h
index 329efb0828..dddf7d032f 100644
--- a/direct/src/plugin/p3d_plugin.h
+++ b/direct/src/plugin/p3d_plugin.h
@@ -79,7 +79,7 @@ extern "C" {
    (below). This number will be incremented whenever there are changes
    to any of the interface specifications defined in this header
    file. */
-#define P3D_API_VERSION 5
+#define P3D_API_VERSION 6
 
 /************************ GLOBAL FUNCTIONS **************************/
 
@@ -95,12 +95,19 @@ extern "C" {
    file that has already been downloaded and verified from the server.
    If this is NULL, a new file will be downloaded as needed.
 
+   If download_url is not NULL or empty, it specifies the root URL of
+   the download server; otherwise, the compiled-in default is used.
+
+   If platform is not NULL or empty, it specifies the current platform
+   string; otherwise, the compiled-in default is used.
+
    This function returns true if the core API is valid and uses a
    compatible API, false otherwise.  If it returns false, the host
    should not call any more functions in this API, and should
    immediately unload the DLL and (if possible) download a new one. */
 typedef bool 
-P3D_initialize_func(int api_version, const char *contents_filename);
+P3D_initialize_func(int api_version, const char *contents_filename,
+                    const char *download_url, const char *platform);
 
 /* This function should be called to unload the core API.  It will
    release all internally-allocated memory and return the core API to
diff --git a/direct/src/plugin/p3d_plugin_common.h b/direct/src/plugin/p3d_plugin_common.h
index 7446c31780..84443de526 100644
--- a/direct/src/plugin/p3d_plugin_common.h
+++ b/direct/src/plugin/p3d_plugin_common.h
@@ -26,6 +26,11 @@
 #include "p3d_plugin.h"
 #include "p3d_lock.h"
 
+// It's a good idea to pick up this header file, even though we don't
+// actually link with dtool.  This header file defines useful
+// system-wide config settings.
+#include "dtool_config.h"
+
 #include <iostream>
 #include <fstream>
 #include <string>
diff --git a/direct/src/plugin/p3d_plugin_config.h.pp b/direct/src/plugin/p3d_plugin_config.h.pp
index e322c88568..36678f5f68 100644
--- a/direct/src/plugin/p3d_plugin_config.h.pp
+++ b/direct/src/plugin/p3d_plugin_config.h.pp
@@ -16,28 +16,12 @@
 #$[]define P3D_PLUGIN_LOGFILE1 "$[subst \,\\,$[osfilename $[P3D_PLUGIN_LOGFILE1]]]"
 #$[]define P3D_PLUGIN_LOGFILE2 "$[subst \,\\,$[osfilename $[P3D_PLUGIN_LOGFILE2]]]"
 
-/* Temporary: the location at which p3dpython.exe can be found.  Empty
-   string for the default. */
+/* For development only: the location at which p3dpython.exe can be
+   found.  Empty string for the default. */
 #$[]define P3D_PLUGIN_P3DPYTHON "$[subst \,\\,$[osfilename $[P3D_PLUGIN_P3DPYTHON]]]"
 
-/* Temporary: the location at which p3d_plugin.dll can be found.  Empty
-   string for the default. */
+/* For development only: the location at which p3d_plugin.dll/.so can
+   be found.  Empty string for the default. */
 #$[]define P3D_PLUGIN_P3D_PLUGIN "$[subst \,\\,$[osfilename $[P3D_PLUGIN_P3D_PLUGIN]]]"
 
-/* The string that corresponds to this particular platform. */
-#if $[not $[P3D_PLUGIN_PLATFORM]]
-  #if $[WINDOWS_PLATFORM]
-    #define P3D_PLUGIN_PLATFORM win32
-  #elif $[UNIX_PLATFORM]
-    #if $[eq $[shell uname -m], x86_64]
-      #define P3D_PLUGIN_PLATFORM linux.amd64
-    #else
-      #define P3D_PLUGIN_PLATFORM linux.i386
-    #endif
-  #else
-    #define P3D_PLUGIN_PLATFORM osx.i386
-  #endif
-#endif
-#$[]define P3D_PLUGIN_PLATFORM "$[P3D_PLUGIN_PLATFORM]"
-
 #end p3d_plugin_config.h
diff --git a/direct/src/plugin_npapi/ppInstance.cxx b/direct/src/plugin_npapi/ppInstance.cxx
index cdbef6e617..152b6d5ae6 100644
--- a/direct/src/plugin_npapi/ppInstance.cxx
+++ b/direct/src/plugin_npapi/ppInstance.cxx
@@ -20,6 +20,10 @@
 #include "find_root_dir.h"
 #include "mkdir_complete.h"
 
+// We can include this header file to get the DTOOL_PLATFORM
+// definition, even though we don't link with dtool.
+#include "dtool_platform.h"
+
 #include <fstream>
 #include <string.h>  // strcmp()
 
@@ -711,7 +715,7 @@ read_contents_file(const string &contents_filename) {
       const char *name = xpackage->Attribute("name");
       if (name != NULL && strcmp(name, "coreapi") == 0) {
         const char *platform = xpackage->Attribute("platform");
-        if (platform != NULL && strcmp(platform, P3D_PLUGIN_PLATFORM) == 0) {
+        if (platform != NULL && strcmp(platform, DTOOL_PLATFORM) == 0) {
           get_core_api(xpackage);
           return true;
         }
@@ -723,7 +727,7 @@ read_contents_file(const string &contents_filename) {
 
   // Couldn't find the coreapi package description.
   nout << "No coreapi package defined in contents file for "
-       << P3D_PLUGIN_PLATFORM << "\n";
+       << DTOOL_PLATFORM << "\n";
   return false;
 }
 
@@ -932,7 +936,7 @@ do_load_plugin() {
   }
 #endif  // P3D_PLUGIN_P3D_PLUGIN
 
-  if (!load_plugin(pathname, "")) {
+  if (!load_plugin(pathname, "", "", "")) {
     nout << "Unable to launch core API in " << pathname << "\n";
     return;
   }
diff --git a/direct/src/plugin_standalone/panda3d.cxx b/direct/src/plugin_standalone/panda3d.cxx
index e1aa016192..169fecf518 100644
--- a/direct/src/plugin_standalone/panda3d.cxx
+++ b/direct/src/plugin_standalone/panda3d.cxx
@@ -18,6 +18,10 @@
 #include "find_root_dir.h"
 #include "p3d_plugin_config.h"
 
+// We can include this header file to get the DTOOL_PLATFORM
+// definition, even though we don't link with dtool.
+#include "dtool_platform.h"
+
 #include <sstream>
 #ifdef _WIN32
 #include <windows.h>
@@ -54,8 +58,8 @@ run(int argc, char *argv[]) {
   extern int optind;
   const char *optstr = "u:p:fl:t:s:o:h";
 
-  string root_url = P3D_PLUGIN_DOWNLOAD;
-  string this_platform = P3D_PLUGIN_PLATFORM;
+  string download_url = P3D_PLUGIN_DOWNLOAD;
+  string this_platform = DTOOL_PLATFORM;
   bool force_download = false;
 
   Filename output_filename;
@@ -68,7 +72,7 @@ run(int argc, char *argv[]) {
   while (flag != EOF) {
     switch (flag) {
     case 'u':
-      root_url = optarg;
+      download_url = optarg;
       break;
 
     case 'p':
@@ -130,11 +134,11 @@ run(int argc, char *argv[]) {
   }
 
   // Make sure it ends with a slash.
-  if (!root_url.empty() && root_url[root_url.length() - 1] != '/') {
-    root_url += '/';
+  if (!download_url.empty() && download_url[download_url.length() - 1] != '/') {
+    download_url += '/';
   }
 
-  if (!get_plugin(root_url, this_platform, force_download)) {
+  if (!get_plugin(download_url, this_platform, force_download)) {
     cerr << "Unable to load Panda3D plugin.\n";
     return 1;
   }
@@ -284,16 +288,16 @@ run(int argc, char *argv[]) {
 //               true on success, false on failure.
 ////////////////////////////////////////////////////////////////////
 bool Panda3D::
-get_plugin(const string &root_url, const string &this_platform, bool force_download) {
+get_plugin(const string &download_url, const string &this_platform, bool force_download) {
   // First, look for the existing contents.xml file.
   Filename contents_filename = Filename(Filename::from_os_specific(_root_dir), "contents.xml");
-  if (!force_download && read_contents_file(contents_filename, root_url, this_platform)) {
+  if (!force_download && read_contents_file(contents_filename, download_url, this_platform)) {
     // Got the file, and it's good.
     return true;
   }
 
   // Couldn't read it, so go get it.
-  string url = root_url;
+  string url = download_url;
   url += "contents.xml";
   cerr << "Getting URL " << url << "\n";
   
@@ -305,7 +309,7 @@ get_plugin(const string &root_url, const string &this_platform, bool force_downl
     return false;
   }
   
-  return read_contents_file(contents_filename, root_url, this_platform);
+  return read_contents_file(contents_filename, download_url, this_platform);
 }
 
 ////////////////////////////////////////////////////////////////////
@@ -316,7 +320,7 @@ get_plugin(const string &root_url, const string &this_platform, bool force_downl
 //               possible.  Returns true on success, false on failure.
 ////////////////////////////////////////////////////////////////////
 bool Panda3D::
-read_contents_file(Filename contents_filename, const string &root_url, 
+read_contents_file(Filename contents_filename, const string &download_url, 
                    const string &this_platform) {
   ifstream in;
   contents_filename.set_text();
@@ -336,7 +340,8 @@ read_contents_file(Filename contents_filename, const string &root_url,
       if (name != NULL && strcmp(name, "coreapi") == 0) {
         const char *xplatform = xpackage->Attribute("platform");
         if (xplatform != NULL && strcmp(xplatform, this_platform.c_str()) == 0) {
-          return get_core_api(contents_filename, root_url, xpackage);
+          return get_core_api(contents_filename, download_url, this_platform,
+                              xpackage);
         }
       }
       
@@ -359,13 +364,13 @@ read_contents_file(Filename contents_filename, const string &root_url,
 //               if necessary.
 ////////////////////////////////////////////////////////////////////
 bool Panda3D::
-get_core_api(const Filename &contents_filename, const string &root_url, 
-             TiXmlElement *xpackage) {
+get_core_api(const Filename &contents_filename, const string &download_url,
+             const string &this_platform, TiXmlElement *xpackage) {
   _core_api_dll.load_xml(xpackage);
 
   if (!_core_api_dll.quick_verify(_root_dir)) {
     // The DLL file needs to be downloaded.  Go get it.
-    string url = root_url;
+    string url = download_url;
     url += _core_api_dll.get_filename();
     
     Filename pathname = Filename::from_os_specific(_core_api_dll.get_pathname(_root_dir));
@@ -398,7 +403,8 @@ get_core_api(const Filename &contents_filename, const string &root_url,
   }
 #endif  // P3D_PLUGIN_P3D_PLUGIN
 
-  if (!load_plugin(pathname, contents_filename.to_os_specific())) {
+  if (!load_plugin(pathname, contents_filename.to_os_specific(),
+                   download_url, this_platform)) {
     cerr << "Unable to launch core API in " << pathname << "\n" << flush;
     return false;
   }
@@ -670,11 +676,11 @@ usage() {
 
     << "  -u url\n"
     << "    Specify the URL of the Panda3D download server.  The default is\n"
-    << "    " << P3D_PLUGIN_DOWNLOAD << "\n\n"
+    << "    \"" << P3D_PLUGIN_DOWNLOAD << "\" .\n\n"
 
     << "  -p platform\n"
-    << "    Specify the platform to masquerade as.  The default is "
-    << P3D_PLUGIN_PLATFORM << "\n\n";
+    << "    Specify the platform to masquerade as.  The default is \""
+    << DTOOL_PLATFORM << "\" .\n\n";
 }
 
 ////////////////////////////////////////////////////////////////////
diff --git a/direct/src/plugin_standalone/panda3d.h b/direct/src/plugin_standalone/panda3d.h
index aac2547a61..e91aa206b4 100755
--- a/direct/src/plugin_standalone/panda3d.h
+++ b/direct/src/plugin_standalone/panda3d.h
@@ -42,11 +42,13 @@ public:
   int run(int argc, char *argv[]);
 
 private:
-  bool get_plugin(const string &root_url, const string &this_platform,
+  bool get_plugin(const string &download_url, const string &this_platform,
                   bool force_download);
-  bool read_contents_file(Filename contents_filename, const string &root_url, 
+  bool read_contents_file(Filename contents_filename, 
+                          const string &download_url,
                           const string &this_platform);
-  bool get_core_api(const Filename &contents_filename, const string &root_url,
+  bool get_core_api(const Filename &contents_filename, 
+                    const string &download_url, const string &this_platform,
                     TiXmlElement *xpackage);
   void run_getters();
   void handle_request(P3D_request *request);