Check SAL_USE_COMMON_LAYOUT envar in one place

Makes it easier to flip the switch in the future (or even do something
more fancy other than checking envvar).

Change-Id: Ie42ca012c167b2108f0fca1ce9ff7beee95f1be7

vcl/inc/sallayout.hxx

@@ -201,6 +201,8 @@ public:
     virtual std::shared_ptr<vcl::TextLayoutCache>
         CreateTextLayoutCache(OUString const&) const;
 
+    static bool     UseCommonLayout();
+
 protected:
     // used by layout engines
                     SalLayout();

vcl/quartz/ctlayout.cxx

@@ -782,7 +782,7 @@ void CTLayout::Simplify( bool /*bIsBase*/ ) {}
 
 SalLayout* CoreTextStyle::GetTextLayout() const
 {
-    if (getenv("SAL_USE_COMMON_LAYOUT"))
+    if (SalLayout::UseCommonLayout())
         return new CommonSalLayout(*this);
     else
         return new CTLayout( this);

vcl/source/gdi/sallayout.cxx

@@ -768,6 +768,12 @@ bool SalLayout::IsSpacingGlyph( sal_GlyphId nGlyph )
     return bRet;
 }
 
+bool SalLayout::UseCommonLayout()
+{
+    static bool bUse = getenv("SAL_USE_COMMON_LAYOUT") != nullptr;
+    return bUse;
+}
+
 GenericSalLayout::GenericSalLayout()
 {}
 

vcl/unx/generic/gdi/cairotextrender.cxx

@@ -532,7 +532,7 @@ SalLayout* CairoTextRender::GetTextLayout( ImplLayoutArgs& rArgs, int nFallbackL
     if( mpServerFont[ nFallbackLevel ]
     && !(rArgs.mnFlags & SalLayoutFlags::DisableGlyphProcessing) )
     {
-        if (getenv("SAL_USE_COMMON_LAYOUT"))
+        if (SalLayout::UseCommonLayout())
         {
             pLayout = new CommonSalLayout(*mpServerFont[nFallbackLevel]);
         }

vcl/win/gdi/winlayout.cxx

@@ -3826,7 +3826,7 @@ SalLayout* WinSalGraphics::GetTextLayout( ImplLayoutArgs& rArgs, int nFallbackLe
     const WinFontFace& rFontFace = *mpWinFontData[ nFallbackLevel ];
     WinFontInstance& rFontInstance = *mpWinFontEntry[ nFallbackLevel ];
 
-    if (getenv("SAL_USE_COMMON_LAYOUT"))
+    if (SalLayout::UseCommonLayout())
     {
         return new CommonSalLayout(this, rFontInstance, rFontFace);
     }