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

vcl/README.vars

@@ -21,6 +21,8 @@ EMF_PLUS_DISABLE - use EMF rendering and ignore EMF+ specifics
 OpenGL
 ------
 SAL_FORCEGL - force enable OpenGL
+SAL_GL_NO_SWAP - disable buffer swapping if set (should show nothing)
+SAL_GL_SLEEP_ON_SWAP - sleep for half a second on each swap-buffers.
 SAL_WITHOUT_WIDGET_CACHE - disable LRU caching of native widget texutres
 SAL_DISABLE_GLYPH_CACHING - don't render glyphs through OpenGL textures
 SAL_DISABLE_GL_WATCHDOG - don't start the thread that watches for broken GL drivers

vcl/inc/opengl/texture.hxx

@@ -37,6 +37,8 @@ public:
     int    mnWidth;
     int    mnHeight;
     GLenum mnFilter;
+    GLuint mnOptStencil;
+    bool   mbHasOptStencil;
 
     std::unique_ptr<std::vector<int>> mpSlotReferences;
     int mnFreeSlots;
@@ -76,7 +78,8 @@ public:
     }
 
     bool InitializeSlots(int nSlotSize);
-    int FindFreeSlot();
+    int  FindFreeSlot();
+    GLuint AddStencil();
 };
 
 class VCL_DLLPUBLIC OpenGLTexture
@@ -110,6 +113,9 @@ public:
     void            Bind();
     void            Unbind();
     void            Read( GLenum nFormat, GLenum nType, sal_uInt8* pData );
+    GLuint          AddStencil();
+    bool            HasStencil() const;
+    GLuint          StencilId() const;
 
     void            SaveToFile(const OUString& rFileName);
 

vcl/inc/opengl/win/gdiimpl.hxx

@@ -31,7 +31,6 @@ public:
 
 protected:
     virtual rtl::Reference<OpenGLContext> CreateWinContext() override;
-    virtual bool UseContext( const rtl::Reference<OpenGLContext> &pContext ) override;
 
     bool RenderTextureCombo(TextureCombo& rCombo, int nX, int nY);
 

vcl/inc/opengl/x11/gdiimpl.hxx

@@ -29,7 +29,6 @@ public:
 
 protected:
     virtual rtl::Reference<OpenGLContext> CreateWinContext() override;
-    virtual bool UseContext( const rtl::Reference<OpenGLContext> &pContext ) override;
 
     bool RenderPixmap(X11Pixmap* pPixmap, X11Pixmap* pMask, int nX, int nY, TextureCombo& rCombo);
 

vcl/inc/openglgdiimpl.hxx

@@ -52,12 +52,20 @@ struct TextureCombo
     std::unique_ptr<OpenGLTexture> mpMask;
 };
 
+class OpenGLFlushIdle;
+
 class VCL_DLLPUBLIC OpenGLSalGraphicsImpl : public SalGraphicsImpl
 {
     friend class OpenGLTests;
 protected:
 
+    /// This context is solely for blitting @maOffscreenTex
+    rtl::Reference<OpenGLContext> mpWindowContext;
+
+    /// This context is whatever is most convenient to render
+    /// to @maOffscreenTex with.
     rtl::Reference<OpenGLContext> mpContext;
+
     SalGraphics& mrParent;
     /// Pointer to the SalFrame or SalVirtualDevice
     SalGeometryProvider* mpProvider;
@@ -67,12 +75,19 @@ protected:
     /// Is it someone else's context we shouldn't be fiddling with ?
     static bool IsForeignContext(const rtl::Reference<OpenGLContext> &xContext);
 
+    /// This idle handler is used to swap buffers after rendering.
+    OpenGLFlushIdle *mpFlush;
+
     // clipping
     vcl::Region maClipRegion;
     bool mbUseScissor;
     bool mbUseStencil;
 
-    bool mbOffscreen;
+    /**
+     * All rendering happens to this off-screen texture. For
+     * non-virtual devices, ie. windows - we will blit it and
+     * swapBuffers later.
+     */
     OpenGLTexture maOffscreenTex;
 
     SalColor mnLineColor;
@@ -80,6 +95,8 @@ protected:
 #ifdef DBG_UTIL
     bool mProgramIsSolidColor;
 #endif
+    sal_uInt32 mnDrawCount;
+    sal_uInt32 mnDrawCountAtFlush;
     SalColor mProgramSolidColor;
     double mProgramSolidTransparency;
 
@@ -131,7 +148,10 @@ public:
     // get the height of the device
     GLfloat GetHeight() const { return mpProvider ? mpProvider->GetHeight() : 1; }
 
-    // check whether this instance is used for offscreen rendering
+    /**
+     * check whether this instance is used for offscreen (Virtual Device)
+     * rendering ie. does it need its own context.
+     */
     bool IsOffscreen() const { return mpProvider == nullptr || mpProvider->IsOffScreen(); }
 
     // operations to do before painting
@@ -144,14 +164,18 @@ protected:
     bool AcquireContext();
     bool ReleaseContext();
 
-    // retrieve the default context for offscreen rendering
+    /// retrieve the default context for offscreen rendering
     static rtl::Reference<OpenGLContext> GetDefaultContext();
 
-    // create a new context for window rendering
+    /// create a new context for rendering to the underlying window
     virtual rtl::Reference<OpenGLContext> CreateWinContext() = 0;
 
-    // check whether the given context can be used by this instance
-    virtual bool UseContext( const rtl::Reference<OpenGLContext> &pContext ) = 0;
+    /// check whether the given context can be used for off-screen rendering
+    bool UseContext( const rtl::Reference<OpenGLContext> &pContext )
+    {
+        return pContext->isInitialized() &&  // not released by the OS etc.
+               IsForeignContext( pContext ); // a genuine VCL context.
+    }
 
 public:
     OpenGLSalGraphicsImpl(SalGraphics& pParent, SalGeometryProvider *pProvider);
@@ -328,8 +352,12 @@ public:
 
     virtual bool drawGradient(const tools::PolyPolygon& rPolygon, const Gradient& rGradient) override;
 
-    virtual OpenGLContext *beginPaint() override;
-private:
+    /// queue an idle flush of contents of the back-buffer to the screen
+    void flush();
+
+public:
+    /// do flush of contents of the back-buffer to the screen & swap.
+    void doFlush();
 };
 
 #endif

vcl/opengl/framebuffer.cxx

@@ -72,6 +72,16 @@ void OpenGLFramebuffer::AttachTexture( const OpenGLTexture& rTexture )
     mnHeight = rTexture.GetHeight();
     glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, mnAttachedTexture, 0);
     CHECK_GL_ERROR();
+
+    GLuint nStencil = rTexture.StencilId();
+    if( nStencil )
+    {
+        VCL_GL_INFO( "Attaching stencil " << nStencil << " to framebuffer " << (int)mnId );
+        glFramebufferRenderbuffer( GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT,
+                                   GL_RENDERBUFFER, nStencil );
+        CHECK_GL_ERROR();
+    }
+
     GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
     CHECK_GL_ERROR();
     if (status != GL_FRAMEBUFFER_COMPLETE)
@@ -87,6 +97,11 @@ void OpenGLFramebuffer::DetachTexture()
         mnAttachedTexture = 0;
         glFramebufferTexture2D( GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, 0, 0 );
         CHECK_GL_ERROR();
+
+        // FIXME: we could make this conditional on having a stencil ?
+        glFramebufferRenderbuffer( GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT,
+                                   GL_RENDERBUFFER, 0 );
+        CHECK_GL_ERROR();
     }
 }
 

vcl/opengl/texture.cxx

@@ -35,6 +35,7 @@ ImplOpenGLTexture::ImplOpenGLTexture( int nWidth, int nHeight, bool bAllocate )
     mnWidth( nWidth ),
     mnHeight( nHeight ),
     mnFilter( GL_NEAREST ),
+    mnOptStencil( 0 ),
     mnFreeSlots(-1)
 {
     glGenTextures( 1, &mnTexture );
@@ -67,6 +68,7 @@ ImplOpenGLTexture::ImplOpenGLTexture( int nX, int nY, int nWidth, int nHeight )
     mnWidth( nWidth ),
     mnHeight( nHeight ),
     mnFilter( GL_NEAREST ),
+    mnOptStencil( 0 ),
     mnFreeSlots(-1)
 {
     // FIXME We need the window height here
@@ -99,6 +101,7 @@ ImplOpenGLTexture::ImplOpenGLTexture( int nWidth, int nHeight, int nFormat, int
     mnWidth( nWidth ),
     mnHeight( nHeight ),
     mnFilter( GL_NEAREST ),
+    mnOptStencil( 0 ),
     mnFreeSlots(-1)
 {
     if( !mnTexture )
@@ -126,6 +129,21 @@ ImplOpenGLTexture::ImplOpenGLTexture( int nWidth, int nHeight, int nFormat, int
     VCL_GL_INFO( "OpenGLTexture " << mnTexture << " " << nWidth << "x" << nHeight << " from data" );
 }
 
+GLuint ImplOpenGLTexture::AddStencil()
+{
+    assert( mnOptStencil == 0 );
+
+    glGenRenderbuffers( 1, &mnOptStencil );
+    glBindRenderbuffer( GL_RENDERBUFFER, mnOptStencil );
+    CHECK_GL_ERROR();
+    VCL_GL_INFO( "Allocate stencil " << mnWidth << " x " << mnHeight );
+    glRenderbufferStorage( GL_RENDERBUFFER, GL_STENCIL_INDEX,
+                           mnWidth, mnHeight );
+    CHECK_GL_ERROR();
+
+    return mnOptStencil;
+}
+
 ImplOpenGLTexture::~ImplOpenGLTexture()
 {
     VCL_GL_INFO( "~OpenGLTexture " << mnTexture );
@@ -136,9 +154,11 @@ ImplOpenGLTexture::~ImplOpenGLTexture()
         // Check we have been correctly un-bound from all framebuffers.
         ImplSVData* pSVData = ImplGetSVData();
         rtl::Reference<OpenGLContext> pContext = pSVData->maGDIData.mpLastContext;
-        if (pContext.is())
+        if( pContext.is() )
             pContext->UnbindTextureFromFramebuffers( mnTexture );
 
+        if( mnOptStencil != 0 )
+            glDeleteRenderbuffers( 1, &mnOptStencil );
         glDeleteTextures( 1, &mnTexture );
     }
 }
@@ -279,6 +299,24 @@ int OpenGLTexture::GetHeight() const
     return maRect.GetHeight();
 }
 
+bool OpenGLTexture::HasStencil() const
+{
+    return mpImpl && mpImpl->mnOptStencil != 0;
+}
+
+GLuint OpenGLTexture::StencilId() const
+{
+    return mpImpl ? mpImpl->mnOptStencil : 0;
+}
+
+GLuint OpenGLTexture::AddStencil()
+{
+    if (mpImpl)
+        return mpImpl->AddStencil();
+    else
+        return 0;
+}
+
 void OpenGLTexture::GetCoord( GLfloat* pCoord, const SalTwoRect& rPosAry, bool bInverted ) const
 {
     VCL_GL_INFO( "Getting coord " << Id() << " [" << maRect.Left() << "," << maRect.Top() << "] " << GetWidth() << "x" << GetHeight() );
@@ -349,6 +387,10 @@ void OpenGLTexture::Bind()
         glBindTexture( GL_TEXTURE_2D, mpImpl->mnTexture );
         CHECK_GL_ERROR();
     }
+    else
+        VCL_GL_INFO( "OpenGLTexture::Binding invalid texture" );
+
+    CHECK_GL_ERROR();
 }
 
 void OpenGLTexture::Unbind()

vcl/opengl/win/gdiimpl.cxx

@@ -29,21 +29,10 @@ void WinOpenGLSalGraphicsImpl::copyBits( const SalTwoRect& rPosAry, SalGraphics*
 rtl::Reference<OpenGLContext> WinOpenGLSalGraphicsImpl::CreateWinContext()
 {
     rtl::Reference<OpenGLContext> pContext = OpenGLContext::Create();
-    pContext->requestSingleBufferedRendering();
     pContext->init( mrParent.mhLocalDC, mrParent.mhWnd );
     return pContext;
 }
 
-bool WinOpenGLSalGraphicsImpl::UseContext( const rtl::Reference<OpenGLContext> &pContext )
-{
-    if( !pContext.is() || !pContext->isInitialized() || IsForeignContext( pContext ) )
-        return false;
-    if( IsOffscreen() )
-        return true;
-    return pContext->getOpenGLWindow().hWnd == mrParent.mhWnd &&
-           pContext->getOpenGLWindow().hDC == mrParent.mhLocalDC;
-}
-
 void WinOpenGLSalGraphicsImpl::Init()
 {
     if ( !IsOffscreen() && mpContext.is() && mpContext->isInitialized() &&

vcl/opengl/x11/gdiimpl.cxx

@@ -58,18 +58,6 @@ rtl::Reference<OpenGLContext> X11OpenGLSalGraphicsImpl::CreateWinContext()
     return pContext;
 }
 
-bool X11OpenGLSalGraphicsImpl::UseContext( const rtl::Reference<OpenGLContext> &pContext )
-{
-    X11WindowProvider *pProvider = dynamic_cast<X11WindowProvider*>(mrParent.m_pFrame);
-
-    if( !pContext->isInitialized() || IsForeignContext( pContext ) )
-        return false;
-    if( !pProvider )
-        return pContext->getOpenGLWindow().win != None;
-    else
-        return pContext->getOpenGLWindow().win == pProvider->GetX11Window();
-}
-
 void X11OpenGLSalGraphicsImpl::copyBits( const SalTwoRect& rPosAry, SalGraphics* pSrcGraphics )
 {
     OpenGLSalGraphicsImpl *pImpl = pSrcGraphics ? static_cast< OpenGLSalGraphicsImpl* >(pSrcGraphics->GetImpl()) : static_cast< OpenGLSalGraphicsImpl *>(mrParent.GetImpl());

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 "OpenGLWrapper.hxx"
@@ -1486,6 +1488,14 @@ 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()