tdf#93867 - clear current GL context before thread switch.

Fixes regression from otherwise a nice cleanup in:
    d2009225

Also get polarity of debug logging only with a context right.

Change-Id: Id322471f01e5656e758aefc57b0d4d5ad073ec54
Reviewed-on: https://gerrit.libreoffice.org/18282Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

include/vcl/opengl/OpenGLContext.hxx

@@ -212,7 +212,10 @@ public:
 
     /// Is this GL context the current context ?
     bool isCurrent();
+    /// release bound resources from the current context
     static void clearCurrent();
+    /// release contexts etc. before (potentially) allowing another thread run.
+    static void prepareForYield();
     /// Is there a current GL context ?
     static bool hasCurrent();
     /// make this GL context current - so it is implicit in subsequent GL calls

vcl/generic/app/geninst.cxx

@@ -55,7 +55,7 @@ void SalYieldMutex::release()
     {
         if ( mnCount == 1 )
         {
-            OpenGLContext::clearCurrent();
+            OpenGLContext::prepareForYield();
             mnThreadId = 0;
         }
         mnCount--;

vcl/osx/salinst.cxx

@@ -271,7 +271,7 @@ void SalYieldMutex::release()
     {
         if ( mnCount == 1 )
         {
-            // TODO: add OpenGLContext::clearCurrent with vcl OpenGL support
+            // TODO: add OpenGLContext::prepareForYield with vcl OpenGL support
             mnThreadId = 0;
         }
         mnCount--;

vcl/source/opengl/OpenGLContext.cxx

@@ -1424,6 +1424,20 @@ void OpenGLContext::clearCurrent()
         pCurrentCtx->ReleaseFramebuffers();
 }
 
+void OpenGLContext::prepareForYield()
+{
+    ImplSVData* pSVData = ImplGetSVData();
+
+    SAL_INFO("vcl.opengl", "Unbinding contexts in preparation for yield");
+    // release all framebuffers from the old context so we can re-attach the
+    // texture in the new context
+    OpenGLContext* pCurrentCtx = pSVData->maGDIData.mpLastContext;
+    if( pCurrentCtx && pCurrentCtx->isCurrent() )
+        pCurrentCtx->resetCurrent();
+
+    assert (!hasCurrent());
+}
+
 void OpenGLContext::makeCurrent()
 {
     ImplSVData* pSVData = ImplGetSVData();

vcl/source/opengl/OpenGLHelper.cxx

@@ -698,7 +698,7 @@ void OpenGLHelper::debugMsgPrint(const char *pArea, const char *pFormat, ...)
     vsnprintf(pStr, sizeof(pStr), pFormat, aArgs);
     pStr[sizeof(pStr)-20] = '\0';
 
-    bool bHasContext = !OpenGLContext::hasCurrent();
+    bool bHasContext = OpenGLContext::hasCurrent();
     if (!bHasContext)
         strcat(pStr, "- no GL context");
 

vcl/win/source/app/salinst.cxx

@@ -153,7 +153,7 @@ void SalYieldMutex::release()
         {
             if ( mnCount == 1 )
             {
-                OpenGLContext::clearCurrent();
+                OpenGLContext::prepareForYield();
 
                 // If we don't call these message, the Output from the
                 // Java clients doesn't come in the right order
@@ -176,7 +176,10 @@ void SalYieldMutex::release()
         else
         {
             if ( mnCount == 1 )
+            {
                 mnThreadId = 0;
+                OpenGLContext::prepareForYield();
+            }
             mnCount--;
             m_mutex.release();
         }