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.net - Calculating the positions of glyphs in Windows

Is there any simple and compatible GDI or .NET accessible subsystem of Windows that will give glyph position characters. The task here is the combining symbols such as those in Arabic which sometimes have chains of multiple combining symbols stacking on top of each others such as Arabic Fatha + Arabic Letter Superscript Alef + Arabic Maddah Above. The trouble is that though the X positions can be determined precisely with GDI GetCharacterPlacement, the Y position calculations which are derived from OpenType or TrueType font tables and anchors and a complex set of rules, is not available. Ultimately, to generate a PDF with Arabic properly formatted, the Y positions are needed and precisely. Studying Microsoft Word 2013's save as PDF feature, it is clear they have a way of properly gathering this data as studying the PDF details shows that each character is displayed at its precise position including the combining symbols.

WPF may contain some functions to do this in the GlyphRun class property GlyphOffsets. DirectWrite has the IDWriteTextAnalyzer interface which method GetGlyphPlacements can return DWRITE_GLYPH_OFFSETs and many other complex script information. Looking at the GDI Display and Printer Drive functions, STROBJ_bEnumPositionsOnly seems to return a set of GLYPHPOS structures with this information. GDI certainly renders this correctly under all circumstances if you send the full text to render but not if you want to do it glyph by glyph.

IXpsOMGlyphs in the XPS Object Model allows for a GetGlyphIndices call returning a set of XPS_GLYPH_INDEX gives horizontalOffset and verticalOffset though this library is hardly appropriate.

In the end the only appropriate library looks to be Uniscribe which is complex to use but supported since Internet Explorer 5 and Windows 2000 as opposed to all the other discussions beyond GDI which are generally Vista and later or requiring special dependencies. ScriptItemize returns an array of SCRIPT_STRING_ANALYSIS which can be passed to ScriptShape then ScriptPlace returning an array o GOFFSETs. In fact Uniscribe will given information about word breaks, diacritics, directional flow and many other aspects of what is happening in a complex script. I just wanted to know if there is a simpler method or if this is the minimum required and exact appropriate for such a task since Uniscribe appears to be extremely difficult to use directly from .NET and reasonably would need a C++ wrapper since there are a great deal of structures and pointers.

Update and answer: Uniscribe will not work for PDF purposes as it uses integers in GDI device units thus the accuracy is greatly compromised. Probably why Microsoft Word 2013 finally supports native PDF conversion support because ultimately DirectWrite seems to be relied upon. As mentioned below I posted both code solutions in .NET as tips on CodeProject. DirectWrite seems to be the only answer beyond designing a custom font shaping and calculation engine.

question from:https://stackoverflow.com/questions/65933403/arabic-ligatures-glyphs-on-windows

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Sample Uniscribe code in .NET since it is not available on the web currently:

     _
    Public Structure GCP_RESULTS
        Public StructSize As UInteger
         _
        Public OutString As String
        Public Order As IntPtr
        Public Dx As IntPtr
        Public CaretPos As IntPtr
        Public [Class] As IntPtr
        Public Glyphs As IntPtr
        Public GlyphCount As UInteger
        Public MaxFit As Integer
    End Structure
     _
    Public Structure SCRIPT_CONTROL
        Public ScriptControlFlags As UInteger
    End Structure
     _
    Public Structure SCRIPT_STATE
        Public ScriptStateFlags As UShort
    End Structure
     _
    Public Structure SCRIPT_ANALYSIS
        Public ScriptAnalysisFlags As UShort
        Public s As SCRIPT_STATE
    End Structure
     _
    Public Structure SCRIPT_VISATTR
        Public ScriptVisAttrFlags As UShort
    End Structure
     _
    Public Structure SCRIPT_ITEM
        Public iCharPos As Integer
        Public a As SCRIPT_ANALYSIS
    End Structure
     _
    Public Structure GOFFSET
        Public du As Integer
        Public dv As Integer
    End Structure
     _
    Public Structure ABC
        Public abcA As Integer
        Public abcB As UInteger
        Public abcC As Integer
    End Structure
    Public Const E_OUTOFMEMORY As Integer = &H8007000E
    Public Const E_PENDING As Integer = &H8000000A
    Public Const USP_E_SCRIPT_NOT_IN_FONT As Integer = &H80040200
     _
    Public Shared Function GetCharacterPlacement(hdc As IntPtr,  lpString As String, nCount As Integer, nMaxExtent As Integer,  ByRef lpResults As GCP_RESULTS, dwFlags As UInteger) As UInteger
    End Function
     _
    Public Shared Function ScriptItemize( wcInChars As String, cInChars As Integer, cMaxItems As Integer, psControl As SCRIPT_CONTROL, psState As SCRIPT_STATE,  pItems() As SCRIPT_ITEM,  ByRef pcItems As Integer) As Integer
    End Function
     _
    Public Shared Function ScriptShape(hdc As IntPtr, ByRef psc As IntPtr,  wcChars As String, cChars As Integer, cMaxGlyphs As Integer, ByRef psa As SCRIPT_ANALYSIS,  wOutGlyphs() As UShort,  wLogClust() As UShort,  psva() As SCRIPT_VISATTR,  ByRef cGlyphs As Integer) As Integer
    End Function
     _
    Public Shared Function ScriptPlace(hdc As IntPtr, ByRef psc As IntPtr, wGlyphs() As UShort, cGlyphs As Integer, psva() As SCRIPT_VISATTR, ByRef psa As SCRIPT_ANALYSIS,  iAdvance() As Integer,  pGoffset() As GOFFSET,  ByRef pABC As ABC) As Integer
    End Function
     _
    Public Shared Function ScriptFreeCache(ByRef psc As IntPtr) As Integer
    End Function
     _
    Public Shared Function GetDC(hWnd As IntPtr) As IntPtr
    End Function
     _
    Public Shared Function ReleaseDC(hWnd As IntPtr, hdc As IntPtr) As Integer
    End Function
     _
    Private Shared Function SelectObject(ByVal hdc As IntPtr, ByVal hObject As IntPtr) As IntPtr
    End Function
    Structure CharPosInfo
        Public Index As Integer
        Public Width As Integer
        Public PriorWidth As Integer
        Public X As Integer
        Public Y As Integer
    End Structure
    Public Shared Function GetWordDiacriticPositions(Str As String, useFont As Font) As CharPosInfo()
        Dim hdc As IntPtr
        Dim CharPosInfos As New List(Of CharPosInfo)
        hdc = GetDC(IntPtr.Zero) 'desktop device context
        Dim oldFont As IntPtr = SelectObject(hdc, useFont.ToHfont())
        Dim MaxItems As Integer = 16
        Dim Control As New SCRIPT_CONTROL With {.ScriptControlFlags = 0}
        Dim State As New SCRIPT_STATE With {.ScriptStateFlags = 1} '0 LTR, 1 RTL
        Dim Items() As SCRIPT_ITEM = Nothing
        Dim ItemCount As Integer
        Dim Result As Integer
        Do
            ReDim Items(MaxItems - 1)
            Result = ScriptItemize(Str, Str.Length, MaxItems, Control, State, Items, ItemCount)
            If Result = 0 Then
                ReDim Preserve Items(ItemCount) 'there is a dummy last item so adding one here
                Exit Do
            ElseIf Result = E_OUTOFMEMORY Then
            End If
            MaxItems *= 2
        Loop While True
        If Result = 0 Then
            'last item is dummy item pointing to end of string
            Dim Cache As IntPtr = IntPtr.Zero
            For Count = 0 To ItemCount - 2
                Dim Logs() As UShort = Nothing
                Dim Glyphs() As UShort = Nothing
                Dim VisAttrs() As SCRIPT_VISATTR = Nothing
                ReDim Glyphs((Items(Count + 1).iCharPos - Items(Count).iCharPos) * 3  2 + 16 - 1)
                ReDim VisAttrs((Items(Count + 1).iCharPos - Items(Count).iCharPos) * 3  2 + 16 - 1)
                ReDim Logs(Items(Count + 1).iCharPos - Items(Count).iCharPos - 1)
                Dim dc As IntPtr = IntPtr.Zero
                Do
                    Dim GlyphsUsed As Integer
                    Result = ScriptShape(dc, Cache, Str.Substring(Items(Count).iCharPos), Items(Count + 1).iCharPos - Items(Count).iCharPos, Glyphs.Length, Items(Count).a, Glyphs, Logs, VisAttrs, GlyphsUsed)
                    If Result = 0 Then
                        ReDim Preserve Glyphs(GlyphsUsed - 1)
                        ReDim Preserve VisAttrs(GlyphsUsed - 1)
                        Exit Do
                    ElseIf Result = E_PENDING Then
                        dc = hdc
                    ElseIf Result = E_OUTOFMEMORY Then
                        ReDim Glyphs(Glyphs.Length * 2 - 1)
                        ReDim VisAttrs(VisAttrs.Length * 2 - 1)
                    ElseIf Result = USP_E_SCRIPT_NOT_IN_FONT Then
                    Else
                    End If
                Loop While True
                If Result = 0 Then
                    Dim Advances(Glyphs.Length - 1) As Integer
                    Dim Offsets(Glyphs.Length - 1) As GOFFSET
                    Dim abc As New ABC With {.abcA = 0, .abcB = 0, .abcC = 0}
                    dc = IntPtr.Zero
                    Do
                        Result = ScriptPlace(dc, Cache, Glyphs, Glyphs.Length, VisAttrs, Items(Count).a, Advances, Offsets, abc)
                        If Result  E_PENDING Then Exit Do
                        dc = hdc
                    Loop While True
                    If Result = 0 Then
                        Dim LastPriorWidth As Integer = 0
                        Dim RunStart As Integer = 0
                        For CharCount = 0 To Logs.Length - 1
                            Dim PriorWidth As Integer = 0
                            Dim RunCount As Integer = 0
                            For ResCount As Integer = Logs(CharCount) To If(CharCount = Logs.Length - 1, 0, Logs(CharCount + 1)) Step -1
                                'fDiacritic or fZeroWidth
                                If (VisAttrs(ResCount).ScriptVisAttrFlags And (32 Or 64))  0 Then
                                    CharPosInfos.Add(New CharPosInfo With {.Index = RunStart + RunCount, .PriorWidth = LastPriorWidth, .Width = Advances(ResCount), .X = Offsets(ResCount).du, .Y = Offsets(ResCount).dv})
                                End If
                                If CharCount = Logs.Length - 1 OrElse Logs(CharCount)  Logs(CharCount + 1) Then
                                    PriorWidth += Advances(ResCount)
                                    RunCount += 1
                                End If
                            Next
                            LastPriorWidth += PriorWidth
                            If CharCount = Logs.Length - 1 OrElse Logs(CharCount)  Logs(CharCount + 1) Then
                                RunStart = CharCount + 1
                            End If
                        Next
                    End If
                End If
            Next
            ScriptFreeCache(Cache)
        End If
        SelectObject(hdc, oldFont)
        ReleaseDC(IntPtr.Zero, hdc)
        Return CharPosInfos.ToArray()
    End Function

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