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diff --git a/include/vcl/vcllayout.hxx b/include/vcl/vcllayout.hxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#ifndef INCLUDED_VCL_VCLLAYOUT_HXX
+#define INCLUDED_VCL_VCLLAYOUT_HXX
+
+#include <basegfx/polygon/b2dpolypolygon.hxx>
+#include <tools/gen.hxx>
+#include <vcl/devicecoordinate.hxx>
+#include <vcl/dllapi.h>
+
+class ImplLayoutArgs;
+class PhysicalFontFace;
+class SalGraphics;
+class GlyphItem;
+class SalLayoutGlyphs;
+
+// all positions/widths are in font units
+// one exception: drawposition is in pixel units
+
+// Unfortunately there is little documentation to help implementors of
+// new classes derived from SalLayout ("layout engines"), and the code
+// and data structures are far from obvious.
+
+// For instance, I *think* the important virtual functions in the
+// layout engines are called in this order:
+
+// * InitFont()
+// * LayoutText()
+// * AdjustLayout(), any number of times (but presumably
+// usually not at all or just once)
+// * Optionally, DrawText()
+
+// Functions that just return information like GetTexWidth() and
+// FillDXArray() are called after LayoutText() and before DrawText().
+
+// Another important questions is which parts of an ImplLayoutArgs can
+// be changed by callers between LayoutText() and AdjustLayout()
+// calls. It probably makes sense only if one assumes that the "string
+// related inputs" part are not changed after LayoutText().
+
+// But why use the same ImplLayoutArgs structure as parameter for both
+// LayoutText() and AdjustLayout() in the first place? And why
+// duplicate some of the fields in both SalLayout and ImplLayoutArgs
+// (mnMinCharPos, mnEndCharPos, mnLayoutFlags==mnFlags,
+// mnOrientation)? Lost in history...
+
+class VCL_DLLPUBLIC SalLayout
+{
+public:
+    virtual         ~SalLayout();
+    // used by upper layers
+    Point&          DrawBase()                              { return maDrawBase; }
+    const Point&    DrawBase() const                        { return maDrawBase; }
+    Point&          DrawOffset()                            { return maDrawOffset; }
+    const Point&    DrawOffset() const                      { return maDrawOffset; }
+    Point           GetDrawPosition( const Point& rRelative = Point(0,0) ) const;
+
+    virtual bool    LayoutText( ImplLayoutArgs&, const SalLayoutGlyphs* ) = 0;  // first step of layouting
+    virtual void    AdjustLayout( ImplLayoutArgs& );    // adjusting after fallback etc.
+    virtual void    InitFont() const {}
+    virtual void    DrawText( SalGraphics& ) const = 0;
+
+    int             GetUnitsPerPixel() const                { return mnUnitsPerPixel; }
+    int             GetOrientation() const                  { return mnOrientation; }
+
+    // methods using string indexing
+    virtual sal_Int32 GetTextBreak(DeviceCoordinate nMaxWidth, DeviceCoordinate nCharExtra, int nFactor) const = 0;
+    virtual DeviceCoordinate FillDXArray( DeviceCoordinate* pDXArray ) const = 0;
+    virtual DeviceCoordinate GetTextWidth() const { return FillDXArray( nullptr ); }
+    virtual void    GetCaretPositions( int nArraySize, long* pCaretXArray ) const = 0;
+    virtual bool    IsKashidaPosValid ( int /*nCharPos*/ ) const { return true; } // i60594
+
+    // methods using glyph indexing
+    virtual bool    GetNextGlyph(const GlyphItem** pGlyph, Point& rPos, int& nStart,
+                                 const PhysicalFontFace** pFallbackFont = nullptr,
+                                 int* const pFallbackLevel = nullptr) const = 0;
+    virtual bool GetOutline(basegfx::B2DPolyPolygonVector&) const;
+    bool GetBoundRect(tools::Rectangle&) const;
+
+    virtual const SalLayoutGlyphs* GetGlyphs() const;
+
+protected:
+    // used by layout engines
+    SalLayout();
+
+private:
+    SalLayout(const SalLayout&) = delete;
+    SalLayout& operator=(const SalLayout&) = delete;
+
+protected:
+    int             mnMinCharPos;
+    int             mnEndCharPos;
+
+    int             mnUnitsPerPixel;
+    int             mnOrientation;
+
+    mutable Point   maDrawOffset;
+    Point           maDrawBase;
+};
+
+#endif // INCLUDED_VCL_VCLLAYOUT_HXX
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */