Fixed a bug with threads and OpenGL context sharing

git-svn-id: https://sfml.svn.sourceforge.net/svnroot/sfml/branches/sfml2@1567 4e206d99-4929-0410-ac5d-dfc041789085

include/SFML/Graphics/RenderTarget.hpp

@@ -63,7 +63,7 @@ public :
     /// \param color Fill color to use to clear the render target
     ///
     ////////////////////////////////////////////////////////////
-    void Clear(const Color& color = Color(0, 0, 0));
+    void Clear(const Color& color = Color(0, 0, 0, 255));
 
     ////////////////////////////////////////////////////////////
     /// \brief Draw an object into the target

src/SFML/Window/Linux/GlxContext.cpp

@@ -62,7 +62,14 @@ myOwnsWindow(true)
     CreateContext(shared, VideoMode::GetDesktopMode().BitsPerPixel, ContextSettings(0, 0, 0));
 
     // Activate the context
+    if (shared)
         SetActive(true);
+
+    // -- Warning --
+    // The "if (shared)" condition fixes this bug:
+    // http://www.sfml-dev.org/forum/viewtopic.php?p=20767#20767
+    // However, it was already there before and removed at revision 1236,
+    // but without any comment... so it might cause other problems in the future
 }
 
 

src/SFML/Window/Win32/WglContext.cpp

@@ -59,7 +59,14 @@ myOwnsWindow   (true)
         CreateContext(shared, VideoMode::GetDesktopMode().BitsPerPixel, ContextSettings(0, 0, 0));
 
     // Activate the context
+    if (shared)
         SetActive(true);
+
+    // -- Warning --
+    // The "if (shared)" condition fixes this bug:
+    // http://www.sfml-dev.org/forum/viewtopic.php?p=20767#20767
+    // However, it was already there before and removed at revision 1236,
+    // but without any comment... so it might cause other problems in the future
 }