vcl: make OpenGLContext::makeCurrent unfeasibly faster.

Don't set the same context if it is already set. Apparently this is
something that is unbelievably costly on Windows, and very costly on
Linux. Instead check if the context is already set, and don't re-set it.

Change-Id: If4fed3e555e1388031446be76d6fdfde5b9f13e5

vcl/source/opengl/OpenGLContext.cxx

@@ -1073,7 +1073,11 @@ SystemWindowData OpenGLContext::generateWinData(vcl::Window* pParent, bool)
 void OpenGLContext::makeCurrent()
 {
 #if defined( WNT )
-    if (!wglMakeCurrent(m_aGLWin.hDC, m_aGLWin.hRC))
+    if (wglGetCurrentContext() == m_aGLWin.hRC)
+    {
+        SAL_INFO("vcl.opengl", "OpenGLContext::makeCurrent(): Avoid setting the same context");
+    }
+    else if (!wglMakeCurrent(m_aGLWin.hDC, m_aGLWin.hRC))
     {
         SAL_WARN("vcl.opengl", "OpenGLContext::makeCurrent(): wglMakeCurrent failed: " << GetLastError());
     }
@@ -1083,7 +1087,11 @@ void OpenGLContext::makeCurrent()
 #elif defined( IOS ) || defined( ANDROID )
     // nothing
 #elif defined( UNX )
-    if (!glXMakeCurrent( m_aGLWin.dpy, mbPixmap ? m_aGLWin.glPix : m_aGLWin.win, m_aGLWin.ctx ))
+    if (glXGetCurrentContext() == m_aGLWin.ctx)
+    {
+        SAL_INFO("vcl.opengl", "OpenGLContext::makeCurrent(): Avoid setting the same context");
+    }
+    else if (!glXMakeCurrent( m_aGLWin.dpy, mbPixmap ? m_aGLWin.glPix : m_aGLWin.win, m_aGLWin.ctx ))
         SAL_WARN("vcl.opengl", "OpenGLContext::makeCurrent failed");
 #endif
 }