vcl opengl: fix setting up debug context on Windows

At least with my AMD card, in case of SAL_FORCEGL=1 the startup crashes
quite early. DrMemory says:

~~Dr.M~~ Error #1: UNADDRESSABLE ACCESS: writing 0x00001414-0x00001415 1 byte(s)
~~Dr.M~~ # 0 atioglxx.dll!DrvPresentBuffers                          +0xd6ea6  (0x09a248f6 <atioglxx.dll+0x1248f6>)
~~Dr.M~~ # 1 atioglxx.dll!DrvPresentBuffers                          +0x3c069c (0x09d0e0ed <atioglxx.dll+0x40e0ed>)
~~Dr.M~~ # 2 vcllo.dll!OpenGLContext::InitGLEW                        [c:\lo\master\vcl\source\opengl\openglcontext.cxx:949]
~~Dr.M~~ # 3 vcllo.dll!OpenGLContext::ImplInit                        [c:\lo\master\vcl\source\opengl\openglcontext.cxx:866]
~~Dr.M~~ # 4 vcllo.dll!OpenGLContext::init                            [c:\lo\master\vcl\source\opengl\openglcontext.cxx:786]
~~Dr.M~~ # 5 vcllo.dll!WinOpenGLSalGraphicsImpl::CreateWinContext     [c:\lo\master\vcl\opengl\win\gdiimpl.cxx:36]

Turns out that in order to enable the GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB
extension, the GL context must be created with WGL_CONTEXT_DEBUG_BIT_ARB
set. It seems that other drivers did not enforce this so far, but in
this case the driver just crashes without this.

Fix the problem by splitting out the debug setup part of InitGLEW() into
a new InitGLEWDebugging(), and at least on Windows call it only after
wglCreateContextAttribsARB() and wglMakeCurrent(). Additionally make
sure that in the debug case the necessary flag is passed to
wglCreateContextAttribsARB().

Change-Id: I6b77e0c06fd85fdae0386a0801f1de1838524586
Reviewed-on: https://gerrit.libreoffice.org/17750Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>

include/vcl/opengl/OpenGLContext.hxx

@@ -234,6 +234,7 @@ public:
 
 private:
     SAL_DLLPRIVATE bool InitGLEW();
+    SAL_DLLPRIVATE void InitGLEWDebugging();
     SAL_DLLPRIVATE bool initWindow();
     SAL_DLLPRIVATE bool ImplInit();
 #if defined( UNX ) && !defined MACOSX && !defined IOS && !defined ANDROID && !defined(LIBO_HEADLESS)

vcl/source/opengl/OpenGLContext.cxx

@@ -771,7 +771,9 @@ bool OpenGLContext::ImplInit()
         }
     }
 
-    return InitGLEW();
+    bool bRet = InitGLEW();
+    InitGLEWDebugging();
+    return bRet;
 }
 
 #elif defined( _WIN32 )
@@ -875,7 +877,14 @@ bool OpenGLContext::ImplInit()
 
     // now setup the shared context; this needs a temporary context already
     // set up in order to work
-    m_aGLWin.hRC = wglCreateContextAttribsARB(m_aGLWin.hDC, hSharedCtx, NULL);
+    int attribs [] =
+    {
+#ifdef DBG_UTIL
+        WGL_CONTEXT_FLAGS_ARB, WGL_CONTEXT_DEBUG_BIT_ARB,
+#endif
+        0
+    };
+    m_aGLWin.hRC = wglCreateContextAttribsARB(m_aGLWin.hDC, hSharedCtx, attribs);
     if (m_aGLWin.hRC == 0)
     {
         ImplWriteLastError(GetLastError(), "wglCreateContextAttribsARB in OpenGLContext::ImplInit");
@@ -884,6 +893,7 @@ bool OpenGLContext::ImplInit()
     }
 
     wglMakeCurrent(NULL, NULL);
+    InitGLEWDebugging();
     wglDeleteContext(hTempRC);
 
     if (!wglMakeCurrent(m_aGLWin.hDC, m_aGLWin.hRC))
@@ -911,7 +921,9 @@ bool OpenGLContext::ImplInit()
     NSOpenGLView* pView = getOpenGLView();
     OpenGLWrapper::makeCurrent(pView);
 
-    return InitGLEW();
+    bool bRet = InitGLEW();
+    InitGLEWDebugging();
+    return bRet;
 }
 
 #else
@@ -940,6 +952,13 @@ bool OpenGLContext::InitGLEW()
             bGlewInit = true;
     }
 
+    SAL_INFO("vcl.opengl", "OpenGLContext::ImplInit----end");
+    mbInitialized = true;
+    return true;
+}
+
+void OpenGLContext::InitGLEWDebugging()
+{
 #ifdef DBG_UTIL
     // only enable debug output in dbgutil build
     if( GLEW_ARB_debug_output)
@@ -957,10 +976,6 @@ bool OpenGLContext::InitGLEW()
     }
 
 #endif
-
-    SAL_INFO("vcl.opengl", "OpenGLContext::ImplInit----end");
-    mbInitialized = true;
-    return true;
 }
 
 void OpenGLContext::setWinPosAndSize(const Point &rPos, const Size& rSize)