tdf#93529 - move to a Mac-like double-buffered OpenGL model.

This moves us to always rendering to an off-screen texture, and then
(at idle) blitting this to the screen & swapping buffers. Ideally we
should never see any rendering, or flicker again with this approach.

Several fixes are included:
+ avoid multiple OpenGL contexts being created for the same window,
created excessive flicker problems.
+ de-virtualize UseContext - which context we use is less critical.
+ kill 'mbOffscreen' distinction - all VCL rendering is offscreen.
+ implement 'doFlush' and high priority idle flushing.
+ bind stencil buffer for clipping vs. textures - fixing complex
clopping when rendering to virtual-devices, and off-screen.
+ document environment. variables.
+ use white as default background glClear color, but red or
random color for DBGUTIL.

Change-Id: I6be08595b6c8deb7e6db0dbd81308b2c97d2b4ff

1 files changed, 10 insertions, 0 deletions

diff --git a/vcl/source/opengl/OpenGLContext.cxx b/vcl/source/opengl/OpenGLContext.cxx
index 26148a607cff..98be555ba5ad 100644
--- a/vcl/source/opengl/OpenGLContext.cxx
+++ b/vcl/source/opengl/OpenGLContext.cxx
@@ -18,6 +18,8 @@
 #include <vcl/bmpacc.hxx>
 #include <vcl/graph.hxx>
 
+#include <osl/thread.hxx>
+
 #if defined(MACOSX)
 #include <premac.h>
 #include <AppKit/NSOpenGLView.h>
@@ -1487,6 +1489,14 @@ void OpenGLContext::swapBuffers()
 #elif defined( UNX )
     glXSwapBuffers(m_aGLWin.dpy, m_aGLWin.win);
 #endif
+
+    static bool bSleep = getenv("SAL_GL_SLEEP_ON_SWAP");
+    if (bSleep)
+    {
+        // half a second.
+        TimeValue aSleep( 0, 500*1000*1000 );
+        osl::Thread::wait( aSleep );
+    }
 }
 
 void OpenGLContext::sync()