tdf#114316 vcl opengl windows: fix missing context menu in full-screen mode

Full-screen mode on Windows used to work by measuring the space needed
by window caption (title) and borders, then positioning and sizing the
window in a way, so that the caption and borders are not visible.

This approach breaks at least in the OpenGL case where a large enough
negative position results in rendering errors.

Fix the problem by explicitly requesting the window to have no caption,
so we render less outside the screen (30 pixels -> 8 pixels in my case),
which makes the "exit fullscreen" toolbar appear, also the context menu
is visible.

Change-Id: I6cf2b9774b505d3887b958a6a018b5ae84bbe4bc
Reviewed-on: https://gerrit.libreoffice.org/70191Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins

vcl/inc/win/salframe.h

@@ -49,6 +49,7 @@ public:
     int                     mnMaxHeight;            // max. client height in pixeln
     RECT                    maFullScreenRect;       // fullscreen rect
     int                     mnFullScreenShowState;  // fullscreen restore show state
+    bool                    mbFullScreenCaption;    // WS_CAPTION reset in full screen mode.
     UINT                    mnInputLang;            // current Input Language
     UINT                    mnInputCodePage;        // current Input CodePage
     SalFrameStyleFlags      mnStyle;                // style

vcl/win/window/salframe.cxx

@@ -843,6 +843,7 @@ WinSalFrame::WinSalFrame()
     mbBorder            = false;
     mbFixBorder         = false;
     mbSizeBorder        = false;
+    mbFullScreenCaption = false;
     mbFullScreen        = false;
     mbPresentation      = false;
     mbInShow            = false;
@@ -1850,6 +1851,15 @@ void WinSalFrame::ShowFullScreen( bool bFullScreen, sal_Int32 nDisplay )
         if ( !(GetWindowStyle( mhWnd ) & WS_VISIBLE) )
             mnShowState = SW_SHOW;
 
+        // Save caption state.
+        mbFullScreenCaption = mbCaption;
+        if (mbCaption)
+        {
+            DWORD nStyle = GetWindowStyle(mhWnd);
+            SetWindowStyle(mhWnd, nStyle & ~WS_CAPTION);
+            mbCaption = false;
+        }
+
         // set window to screen size
         ImplSalFrameFullScreenPos( this, true );
     }
@@ -1865,6 +1875,14 @@ void WinSalFrame::ShowFullScreen( bool bFullScreen, sal_Int32 nDisplay )
             SetWindowExStyle( mhWnd, GetWindowExStyle( mhWnd ) | WS_EX_TOOLWINDOW );
         mbFullScreenToolWin = false;
 
+        // Restore caption state.
+        if (mbFullScreenCaption)
+        {
+            DWORD nStyle = GetWindowStyle(mhWnd);
+            SetWindowStyle(mhWnd, nStyle | WS_CAPTION);
+        }
+        mbCaption = mbFullScreenCaption;
+
         SetWindowPos( mhWnd, nullptr,
                       maFullScreenRect.left,
                       maFullScreenRect.top,