implement concurrent rendering on X11. Still a little flickery when switching in and out of threaded mode; not sure why yet.

stepmania/src/arch/LowLevelWindow/LowLevelWindow_X11.cpp

@@ -20,6 +20,10 @@
 #include <X11/extensions/XTest.h>
 #endif
 
+static GLXContext g_pContext = NULL;
+static GLXContext g_pBackgroundContext = NULL;
+static Window g_AltWindow = 0;
+
 static LocalizedString FAILED_CONNECTION_XSERVER( "LowLevelWindow_X11", "Failed to establish a connection with the X server'" );
 LowLevelWindow_X11::LowLevelWindow_X11()
 {
@@ -131,15 +135,19 @@ RString LowLevelWindow_X11::TryVideoMode( const VideoModeParams &p, bool &bNewDe
 		if( !X11Helper::MakeWindow(xvi->screen, xvi->depth, xvi->visual, p.width, p.height, !p.windowed) )
 			return "Failed to create the window.";
 		
+		g_AltWindow = X11Helper::CreateWindow(xvi->screen, xvi->depth, xvi->visual, p.width, p.height, !p.windowed);
+		ASSERT( g_AltWindow );
+
 		m_bWindowIsOpen = true;
 
 		char *szWindowTitle = const_cast<char *>( p.sWindowTitle.c_str() );
 		XChangeProperty( X11Helper::Dpy, X11Helper::Win, XA_WM_NAME, XA_STRING, 8, PropModeReplace,
 				reinterpret_cast<unsigned char*>(szWindowTitle), strlen(szWindowTitle) );
 
-		GLXContext ctxt = glXCreateContext( X11Helper::Dpy, xvi, NULL, True );
+		g_pContext = glXCreateContext( X11Helper::Dpy, xvi, NULL, True );
+		g_pBackgroundContext = glXCreateContext( X11Helper::Dpy, xvi, g_pContext, True );
 
-		glXMakeCurrent( X11Helper::Dpy, X11Helper::Win, ctxt );
+		glXMakeCurrent( X11Helper::Dpy, X11Helper::Win, g_pContext );
 
 		XMapWindow( X11Helper::Dpy, X11Helper::Win );
 
@@ -296,6 +304,38 @@ void LowLevelWindow_X11::GetDisplayResolutions( DisplayResolutions &out ) const
 	}
 }
 
+bool LowLevelWindow_X11::SupportsThreadedRendering()
+{
+	return g_pBackgroundContext != NULL;
+}
+
+void LowLevelWindow_X11::BeginConcurrentRenderingMainThread()
+{
+	/* Move the main thread, which is going to be loading textures, etc. but
+	 * not rendering, to an undisplayed window.  This results in smoother
+	 * rendering. */
+	bool b = glXMakeCurrent( X11Helper::Dpy, g_AltWindow, g_pContext );
+	ASSERT(b);
+}
+
+void LowLevelWindow_X11::EndConcurrentRenderingMainThread()
+{
+	bool b = glXMakeCurrent( X11Helper::Dpy, X11Helper::Win, g_pContext );
+	ASSERT(b);
+}
+
+void LowLevelWindow_X11::BeginConcurrentRendering()
+{
+	bool b = glXMakeCurrent( X11Helper::Dpy, X11Helper::Win, g_pBackgroundContext );
+	ASSERT(b);
+}
+
+void LowLevelWindow_X11::EndConcurrentRendering()
+{
+	bool b = glXMakeCurrent( X11Helper::Dpy, None, NULL );
+	ASSERT(b);
+}
+
 /*
  * (c) 2005 Ben Anderson
  * All rights reserved.

stepmania/src/arch/LowLevelWindow/LowLevelWindow_X11.h

@@ -21,6 +21,12 @@ public:
 	
 	void GetDisplayResolutions( DisplayResolutions &out ) const;
 
+	bool SupportsThreadedRendering();
+	void BeginConcurrentRenderingMainThread();
+	void EndConcurrentRenderingMainThread();
+	void BeginConcurrentRendering();
+	void EndConcurrentRendering();
+
 private:
 	bool m_bWindowIsOpen;
 	bool m_bWasWindowed;