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

4 files changed, 43 insertions, 11 deletions

diff --git a/vcl/inc/opengl/texture.hxx b/vcl/inc/opengl/texture.hxx
index f67b3348d14d..e57aa9e32306 100644
--- a/vcl/inc/opengl/texture.hxx
+++ b/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);
 
diff --git a/vcl/inc/opengl/win/gdiimpl.hxx b/vcl/inc/opengl/win/gdiimpl.hxx
index ecefede6e7ea..8102d2ef5c07 100644
--- a/vcl/inc/opengl/win/gdiimpl.hxx
+++ b/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);
 
diff --git a/vcl/inc/opengl/x11/gdiimpl.hxx b/vcl/inc/opengl/x11/gdiimpl.hxx
index f07468d6a135..eccd0ef06ae9 100644
--- a/vcl/inc/opengl/x11/gdiimpl.hxx
+++ b/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);
 
diff --git a/vcl/inc/openglgdiimpl.hxx b/vcl/inc/openglgdiimpl.hxx
index 667b2ec095f0..a1c2a2539352 100644
--- a/vcl/inc/openglgdiimpl.hxx
+++ b/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