path: root/docview/components/richtext/RichTextLayoutUnit.pas

Unit RichTextLayoutUnit;

{$mode objfpc}{$H+}

// Dynamically created layout class.
// Represents a laid out rich text document

Interface

Uses
  Classes,
  CanvasFontManager,
  RichTextDocumentUnit,
  RichTextStyleUnit,
  fpg_imagelist,
  contnrs;

Type

  TLayoutLine = class(TObject)
  public
    Text: PChar;
    Length: longint;
    Height: longint;
    Width: longint;
    MaxDescender: longint;
    MaxTextHeight: longint; // maximum height of text, doesn't include images
    LinkIndex: longint; // link index at start of line, if any
    Style: TTextDrawStyle;
    Wrapped: boolean;
  end;


  TLayoutLineList = class(TObjectList)
  protected
    function GetItem(Index: Integer): TLayoutLine; reintroduce;
    procedure SetItem(Index: Integer; const AValue: TLayoutLine); reintroduce;
  public
    function Add(AObject: TLayoutLine): Integer; reintroduce;
    function Remove(AObject: TLayoutLine): Integer; reintroduce;
    function IndexOf(AObject: TLayoutLine): Integer; reintroduce;
    function First: TLayoutLine; reintroduce;
    Function Last: TLayoutLine; reintroduce;
    property Items[Index: Integer]: TLayoutLine read GetItem write SetItem; default;
  end;


  TTextPosition = (
        tpAboveTextArea,
        tpAboveText,
        tpWithinText,
        tpBelowText,
        tpBelowTextArea
      );


  // forward declaration
  TRichTextLayout = class;


//  TLinkEvent = procedure( Sender: TRichTextLayout; Link: string ) of object;


  TRichTextLayout = class(TObject)
  Protected
    FFontManager: TCanvasFontManager;
    FText: PChar;
    FImages: TfpgImageList;
    FLayoutWidth: longint; // The target width for the layout. Used for centreing/right align
    FWidth: longint;       // The actual width of the text. May be wider due to unaligned
                           // parts or bitmaps or width so small individual characters don't fit.
    FHeight: longint;
    FLinks: TStringList;
    FHorizontalImageScale: double;
    FVerticalImageScale: double;
  public
    FLines: TLayoutLineList;
    FNumLines: longint;
    FRichTextSettings: TRichTextSettings;
    // Drawing functions
    Procedure PerformStyleTag( Const Tag: TTag;
                               Var Style: TTextDrawStyle;
                               const X: longint );
    function GetElementWidth( Element: TTextElement ): longint;
    // Queries
    Function GetStartX( Style: TTextDrawStyle; Line: TLayoutLine ): longint;
    Procedure GetXFromOffset( const Offset: longint;
                              const LineIndex: longint;
                              Var X: longint );
    Procedure GetOffsetFromX( const XToFind: longint;
                              const LineIndex: longint;
                              Var Offset: longint;
                              Var Link: string );
    function FindPoint( XToFind, YToFind: longint;
                        Var LineIndex: longint;
                        Var Offset: longint;
                        Var Link: string ): TTextPosition;
    function GetLineFromCharIndex( Index: longint ): longint;
    function GetOffsetFromCharIndex( Index: longint;
                                     Line: longint ): longint;
    function GetLinePosition( Line: longint ): longint;
    function GetLineFromPosition( YToFind: longint;
                                  Var LineIndex: longint;
                                  Var Remainder: longint ): TTextPosition;
    // Layout functions
    Procedure   AddLineStart(var Line: TLayoutLine);
    Procedure   CheckFontHeights(var Line: TLayoutLine);
    Procedure   Layout;
    function    IsValidBitmapIndex( Index: longint ): boolean;
    // property handlers
    Function    GetCharIndex( P: PChar ): longint;
    Function    GetTextEnd: longint;
  public
    constructor Create(Text: PChar; Images: TfpgImageList; RichTextSettings: TRichTextSettings; FontManager: TCanvasFontManager; AWidth: longint);
    destructor  Destroy; Override;
    function    LinkFromIndex( const CharIndexToFind: longint): string;
    property    TextEnd: longint read GetTextEnd;
    property    Images: TfpgImageList read FImages;
    property    Width: longint read FWidth;
    property    Height: longint read FHeight;
    property    HorizontalImageScale: double read FHorizontalImageScale;
    property    VerticalImageScale: double read FVerticalImageScale;
  end;


implementation

uses
  SysUtils,
  ACLStringUtility,
  nvUtilities,
  fpg_main;


{ TLayoutLineList }

function TLayoutLineList.GetItem(Index: Integer): TLayoutLine;
begin
  inherited GetItem(Index);
end;

procedure TLayoutLineList.SetItem(Index: Integer; const AValue: TLayoutLine);
begin
  inherited SetItem(Index, AValue);
end;

function TLayoutLineList.Add(AObject: TLayoutLine): Integer;
begin
  Result := inherited Add(AObject);
end;

function TLayoutLineList.Remove(AObject: TLayoutLine): Integer;
begin
  Result := inherited Remove(AObject);
end;

function TLayoutLineList.IndexOf(AObject: TLayoutLine): Integer;
begin
  Result := inherited IndexOf(AObject);
end;

function TLayoutLineList.First: TLayoutLine;
begin
  Result := TLayoutLine(inherited First);
end;

function TLayoutLineList.Last: TLayoutLine;
begin
  Result := TLayoutLine(inherited Last);
end;


{ TRichTextLayout }

Function TRichTextLayout.GetTextEnd: longint;
begin
  Result := StrLen( FText );
end;

// Create a layout of the specified rich text.
constructor TRichTextLayout.Create(Text: PChar; Images: TfpgImageList;
    RichTextSettings: TRichTextSettings; FontManager: TCanvasFontManager;
    AWidth: longint);
begin
ProfileEvent('DEBUG:  TRichTextLayout.Create >>>>');
  inherited Create;
  FRichTextSettings := RichTextSettings;
  FImages := Images;
  FText := Text;
  FLines := TLayoutLineList.Create;
  FNumLines := 0;
  FLinks := TStringList.Create;
  FLinks.Duplicates := dupIgnore;
  FFontManager := FontManager;
  FLayoutWidth := AWidth;
  FHorizontalImageScale := 1;
  FVerticalImageScale := 1;
  //FHorizontalImageScale :=   FFontManager.Canvas.HorizontalResolution
  //                         / Screen.Canvas.HorizontalResolution;
  //FVerticalImageScale   :=   FFontManager.Canvas.VerticalResolution
  //                         / Screen.Canvas.VerticalResolution;
  Layout;
ProfileEvent('DEBUG:  TRichTextLayout.Create <<<<');
end;

Destructor TRichTextLayout.Destroy;
Begin
  ProfileEvent('TRichTextLayout.Destroy  ******* ');
  FreeAndNil(FLines);
  FLinks.Free;
  FRichTextSettings := nil; // was a reference only
  FImages := nil;  // was a reference only
  FFontManager := nil;  // was a reference only
  inherited Destroy;
End;

Procedure TRichTextLayout.AddLineStart(var Line: TLayoutLine);
begin
  FLines.Add(Line);
  inc( FNumLines );
  ProfileEvent('TRichTextLayout.AddLineStart: FNumLines =' + intToStr(FNumLines));
end;

Procedure TRichTextLayout.PerformStyleTag( Const Tag: TTag;
                                           Var Style: TTextDrawStyle;
                                           const X: longint );
begin
ProfileEvent('TRichTextLayout.PerformStyleTag >>>');
  ApplyStyleTag( Tag,
                 Style,
                 FFontManager,
                 FRichTextSettings,
                 X );
ProfileEvent('TRichTextLayout.PerformStyleTag <<<');
end;

// Check the current font specifications and see if the
// given line needs updating for max height/descender
Procedure TRichTextLayout.CheckFontHeights( Var Line: TLayoutLine );
var
  FontHeight: longint;
  Descender: longint;
begin
  FontHeight := FFontManager.CharHeight;
  Descender := FFontManager.CharDescender;

  if FontHeight > Line.Height then
    Line.Height := FontHeight;

  if FontHeight > Line.MaxTextHeight then
    Line.MaxTextHeight := FontHeight;

  if Descender > Line.MaxDescender then
    Line.MaxDescender := Descender;
end;

function TRichTextLayout.IsValidBitmapIndex( Index: longint ): boolean;
begin
  if FImages = nil then
    Result := false
  else if FImages.Count = 0 then
    Result := false
  else
    Result := Between( Index, 0, FImages.Count - 1 );
end;

// Main procedure: reads through the whole text currently stored
// and breaks up into lines - each represented as a TLayoutLine in
// the LayoutLineList class
Procedure TRichTextLayout.Layout;
Var
  CurrentLine: TLayoutLine;
  CurrentLinkIndex: longint;
  WrapX: longint; // X to wrap at
  WordX: longint; // width of the current word so far
  P: PChar;
  NextP: PChar;
  NextP2: PChar;
  WordStart: PChar;
  WordStarted: boolean; // if false, just skipping spaces..
  WordStartX: longint; // X position of word start
  LineWordsCompleted: longint; // how many words draw so far this line
  CurrentElement: TTextElement;
  NextElement: TTextElement;
  CurrentCharWidth: longint;
  Style: TTextDrawStyle;
  DisplayedCharsSinceFontChange: boolean;
  BitmapIndex: longint;
  Bitmap: TfpgImage;
  BitmapHeight: longint;
  OnBreak: boolean;
  DoWrap: boolean;

  // Nested procedure
  procedure CreateDefaultCurrentLine;
  begin
    CurrentLine := TLayoutLine.Create;
    CurrentLine.Style := Style;
    CurrentLine.Height := 0;
    CurrentLine.MaxDescender := 0;
    CurrentLine.MaxTextHeight := 0;
    CurrentLine.Width := 0;
    CurrentLine.LinkIndex := CurrentLinkIndex;
    CurrentLine.Wrapped := false;
  end;

  Procedure DoLine( EndPoint: PChar; NextLine: PChar; EndX: longint );
  begin
    // check if the max font
    // height needs updating for the last string of the line
    CheckFontHeights( CurrentLine );
    inc( FHeight, CurrentLine.Height );
    CurrentLine.Length := PCharDiff( EndPoint, CurrentLine.Text );
    CurrentLine.Width := EndX;
    if CurrentLine.Width > FWidth then
      FWidth := CurrentLine.Width;
    Assert( CurrentLine.Height > 0 ); // we must have set the line height!
    AddLineStart( CurrentLine );

    CreateDefaultCurrentLine;
    CurrentLine.Text := NextLine;

    assert( CurrentLinkIndex >= -1 );
    assert( CurrentLinkIndex < FLinks.Count );
    WordStartX := Style.LeftMargin;
    // next line
    // reset words completed count
    LineWordsCompleted := 0;
    WordStarted := false;
  end;

begin
ProfileEvent('DEBUG:  TRichTextLayout.Layout  >>>>');
  FNumLines := 0;
  FWidth := FRichTextSettings.Margins.Left;
  FHeight := FRichTextSettings.Margins.Top;
  Style := GetDefaultStyle( FRichTextSettings );
  ApplyStyle( Style, FFontManager );
  CurrentLinkIndex := -1;
  WordStartX := Style.LeftMargin;
  WordX := 0;
  WrapX := FLayoutWidth - FRichTextSettings.Margins.Right;
  LineWordsCompleted := 0;
  WordStarted := false;
  DisplayedCharsSinceFontChange := false;

  P := FText; // P is the current search position

  if FText = '' then
    exit;
  CreateDefaultCurrentLine;
  CurrentLine.Text := P;

  repeat
    CurrentElement := ExtractNextTextElement( P, NextP );
    assert( NextP > P );
    OnBreak := false;
    case CurrentElement.ElementType of
      teWordBreak:
      begin
        CurrentCharWidth := FFontManager.CharWidth( ' ' );
        OnBreak := true;
      end;

      teLineBreak:
      begin
        DoLine( P, NextP, WordStartX + WordX );
        // remember start of line
        WordStart := NextP;
        WordX := 0;
        P := NextP;
        continue;
      end;

      teTextEnd:
      begin
        DoLine( P, NextP, WordStartX + WordX );
        // end of text, so it is safe to free CurrentLine created in DoLine()
        CurrentLine.Free;
        break;
      end;

      teImage:
      begin
        BitmapHeight := 0;
        try
          BitmapIndex := StrToInt( CurrentElement.Tag.Arguments );
        except
          BitmapIndex := -1;
        end;
        Bitmap := nil;
        if IsValidBitmapIndex( BitmapIndex ) then
        begin
          Bitmap := FImages.Items[BitmapIndex].Image;
          CurrentCharWidth := Trunc(Bitmap.Width * FHorizontalImageScale);
          WordStarted := true;
          BitmapHeight := Trunc(Bitmap.Height * FVerticalImageScale);
        end;
      end;

      teText:
      begin
        // Normal (non-leading-space) character
        CurrentCharWidth := FFontManager.CharWidth( CurrentElement.Character );
        WordStarted := true;
      end;

      teStyle:
      begin
        case CurrentElement.Tag.TagType of
          ttBeginLink:
            begin
              CurrentLinkIndex := FLinks.Add( CurrentElement.Tag.Arguments );
              P := NextP;
              continue;
            end;

          ttEndLink:
            begin
              CurrentLinkIndex := -1;
              P := NextP;
              continue;
            end;

          ttSetLeftMargin: // SPECIAL CASE... could affect display immediately
            begin
              PerformStyleTag( CurrentElement.Tag, Style, WordstartX + WordX );
              if Style.LeftMargin < WordStartX then
              begin
                // we're already past the margin being set
                if pos( 'breakifpast', CurrentElement.Tag.Arguments ) > 0 then
                begin
                  // this argument means, do a line break
                  // if the margin is already past
                  // Seems unusual for most purposes, but needed for IPF rendering.
                  DoLine( P, NextP, WordStartX + WordX );

                  // remember start of line
                  WordStart := NextP;
                  WordX := 0;

                  P := NextP;

                  continue;
                end;

                // so ignore it for now.
                P := NextP;
                continue;
              end;

              // skip across to the new margin
              CurrentCharWidth := Style.LeftMargin - WordStartX - WordX;
              // BUT! Don't treat it as a space, because you would not
              // expect wrapping to take place in a margin change...
              // at least not for IPF  :)

            end;  { teSetLeftMargin }
          else
          begin
            // before processing the tag see if font height needs updating
            if DisplayedCharsSinceFontChange then
              CheckFontHeights( CurrentLine );

            if     ( CurrentElement.Tag.TagType = ttItalicOff )
               and ( faItalic in Style.FontAttributes ) then
            begin
              if not FFontManager.IsFixed then
              begin
                // end of italic; add a space
//                inc( WordX, FFontManager.CharWidth( ' ' ) );
              end;
            end;

            PerformStyleTag( CurrentElement.Tag, Style, WordX );

            DisplayedCharsSinceFontChange := false;
            P := NextP;
            continue; // continue loop
          end;
        end;  { case CurrentElement.Tag.TagType of... }
      end  { teStyle }

    end;  { case CurrentElement.ElementType of... }

    if OnBreak then
    begin
      // we just processed a space
      if WordStarted then
      begin
        DisplayedCharsSinceFontChange := true;
        // remember that we have now completed a word on this line
        inc( LineWordsCompleted );
        WordStarted := false;

        // Add the word width, and the space width,
        // to get the start of the next word
        inc( WordStartX, WordX + CurrentCharWidth );
        WordX := 0;

        // remember the start of the next word
        WordStart := NextP;

        P := NextP;

        continue;
      end;
      // else - starting spaces - fall through like normal char
    end;

    // if we're still going here we have a normal char
    // (or leading spaces)
    if not Style.Wrap then
    begin
      // No alignment
      // We don't care about how wide it gets
      inc( WordX, CurrentCharWidth );
      DisplayedCharsSinceFontChange := true;

      if CurrentElement.ElementType = teImage then
        if Bitmap <> nil then
          if BitmapHeight > CurrentLine.Height then
            CurrentLine.Height := BitmapHeight;

      P := NextP;
      continue;
    end;

    DoWrap := false;

    // Calculate position of end of character
    // see if char would exceed width
    if (WordStartX + WordX + CurrentCharWidth) >= WrapX then
    begin
      // reached right hand side before finding end of word
      if LineWordsCompleted > 0 then
        // always wrap after at least one word displayed
        DoWrap := true
      else if not FRichTextSettings.AtLeastOneWordBeforeWrap then
        // only wrap during the first word, if the "at least 1 word" flag is not set.
        DoWrap := true;
    end;

    if DoWrap then
    begin
      if LineWordsCompleted = 0 then
      begin
        // the first word did not fit on the line. so draw
        // as much as will fit
        if WordX = 0 then
        begin
          // even the first char doesn't fit,
          // but draw it anyway (otherwise, infinite loop)
          NextElement := ExtractNextTextElement( NextP, NextP2 );
          if NextElement.ElementType <> teLineBreak then
            // there is still more on the line...
            CurrentLine.Wrapped := true
          else
            // the line ends after this one char or image, we can skip the line end
            NextP := NextP2;

          if CurrentElement.ElementType = teImage then
          begin
            // the only thing on the line is the image. so check height
            if Bitmap <> nil then
              if BitmapHeight > CurrentLine.Height then
                CurrentLine.Height := BitmapHeight;
          end;

          DoLine( NextP, NextP, WordStartX + WordX + CurrentCharWidth );
          WordStart := NextP;
          WordX := 0;
        end
        else
        begin
          CurrentLine.Wrapped := true;
          // at least 1 char fits
          // so draw up to, but not including this char
          DoLine( P,
                  P,
                  WordStartX + WordX );
          WordStart := P;
          WordX := CurrentCharWidth;
        end;
      end
      else
      begin
        // Normal wrap; at least one word fitted on the line
        CurrentLine.Wrapped := true;

        // take the width of the last space of the
        // previous word off the line width
        DoLine( WordStart, // current line ends at start of this word
                WordStart, // next line starts at start of this word
                WordStartX - FFontManager.CharWidth( ' ' ) );
        if CurrentElement.ElementType = teImage then
          if Bitmap <> nil then
            if BitmapHeight > CurrentLine.Height then
              CurrentLine.Height := BitmapHeight;

        // do NOT reset WordX to zero; as we are continuing
        // from partway thru the word on the next line.
        inc( WordX, CurrentCharWidth );
      end;
      WordStarted := true; // by definition, for wrapping
    end
    else
    begin
      // Character fits.
      inc( WordX, CurrentCharWidth );
      DisplayedCharsSinceFontChange := true;
      if CurrentElement.ElementType = teImage then
        if Bitmap <> nil then
          if BitmapHeight > CurrentLine.Height then
            CurrentLine.Height := BitmapHeight;
    end;

    P := NextP;
  until false; // loop is exited by finding end of text

  inc( FHeight, FRichTextSettings.Margins.Bottom );
ProfileEvent('DEBUG:  TRichTextLayout.Layout  <<<<');
End;

Function TRichTextLayout.GetStartX( Style: TTextDrawStyle;
                                    Line: TLayoutLine ): longint;
var
  SpaceOnLine: longint;
begin
  case Style.Alignment of
    taLeft:
      Result := Style.LeftMargin;

    taRight:
      Result :=   Style.LeftMargin + FLayoutWidth
                - Style.RightMargin - Line.Width;

    taCenter:
      begin
        // |<------layout width------------------>|
        // |                                      |
        // |<-lm->[aaaaaaaaaaaaaaa]<-space-><-rm->|
        // |<-----line width------>               |
        // space = layoutw-rm-linew
        SpaceOnLine := FLayoutWidth - Style.RightMargin - Line.Width; // Note: line width includes left margin
        Result := Style.LeftMargin + (SpaceOnLine div 2);
      end;
  end;
end;

Procedure TRichTextLayout.GetOffsetFromX( const XToFind: longint;
                                          const LineIndex: longint;
                                          Var Offset: longint;
                                          Var Link: string );
Var
  X: longint;
  P: PChar;
  NextP: PChar;
  EndP: PChar;
  Element: TTextElement;
  CurrentLink: string;
  Line: TLayoutLine;
  Style: TTextDrawStyle;
  NewMarginX: longint;
  StartedDrawing: boolean;
  fstyle: string;
begin
  Line  := FLines[LineIndex];
  P     := Line.Text;
  EndP  := Line.Text + Line.Length;
  Style := Line.Style;

  fStyle := Style.FontNameSize;
  ApplyFontAttributes(fStyle, Style.FontAttributes);
  FFontManager.SetFont( fStyle );

  StartedDrawing := false;
  Link := '';
  if Line.LinkIndex <> -1 then
    CurrentLink := FLinks[ Line.LinkIndex ]
  else
    CurrentLink := '';

  while P < EndP do
  begin
    Element := ExtractNextTextElement( P, NextP );

    case Element.ElementType of
      teWordBreak,
      teText,
      teImage:
      begin
        if not StartedDrawing then
        begin
          // we haven't yet started drawing:
          // so work out alignment
          X := GetStartX( Style, Line );

          if X > XToFind then
          begin
            // found before the start of the line
            // don't set link
            Offset := 0;
            exit;
          end;

          StartedDrawing := true;

        end;

        // Now find out how wide the thing is
        inc( X, GetElementWidth( Element ) );

        if X > XToFind then
        begin
          // found
          Offset := PCharDiff( P, Line.Text );
          Link := CurrentLink;
          exit;
        end;

      end;

      teStyle:
        case Element.Tag.TagType of
          ttBeginLink:
            CurrentLink := Element.Tag.Arguments;
          ttEndLink:
            CurrentLink := '';
          else
          begin
            if     ( Element.Tag.TagType = ttItalicOff )
               and ( faItalic in Style.FontAttributes )
               and ( not FFontManager.IsFixed ) then
              // end of italic; add a space
//              inc( X, FFontManager.CharWidth( ' ' )  );

            PerformStyleTag( Element.Tag, Style, X );
            NewMarginX := Style.LeftMargin;
            if NewMarginX > X then
            begin
              //skip across...
              X := NewMarginX;
            end;
          end;
        end;
    end;

    P := NextP;
  end;
  Offset := Line.Length;
end;

Procedure TRichTextLayout.GetXFromOffset( const Offset: longint;
                                          const LineIndex: longint;
                                          Var X: longint );
Var
  P: PChar;
  NextP: PChar;
  EndP: PChar;
  Element: TTextElement;
  StartedDrawing: boolean;
  Line: TLayoutLine;
  Style: TTextDrawStyle;
  NewMarginX: longint;
  fStyle: string;
begin
  Line := FLines[LineIndex];
  P := Line.Text;
  EndP := Line.Text + Line.Length;

  Style := Line.Style;
  fStyle := Style.FontNameSize;
  ApplyFontAttributes(fStyle, Style.FontAttributes);
  FFontManager.SetFont( fStyle );

  StartedDrawing := false;

  while P < EndP do
  begin
    Element := ExtractNextTextElement( P, NextP );

    case Element.ElementType of
      teWordBreak,
      teText,
      teImage:
      begin
        if not StartedDrawing then
        begin
          // we haven't yet started drawing:
          // so work out alignment
          X := GetStartX( Style, Line );
          StartedDrawing := true;
        end;

        if GetCharIndex( P ) - GetCharIndex( Line.Text ) >= Offset then
        begin
          // found
          exit;
        end;

        // Now find out how wide the thing is
        inc( X, GetElementWidth( Element ) );

      end;

      teStyle:
      begin
        if     ( Element.Tag.TagType = ttItalicOff )
           and ( faItalic in Style.FontAttributes )
           and ( not FFontManager.IsFixed ) then
          // end of italic; add a space
//          inc( X, FFontManager.CharWidth( ' ' )  );

        PerformStyleTag( Element.Tag, Style, X );

        NewMarginX := Style.LeftMargin;
        if NewMarginX > X then
        begin
          //skip across...
          X := NewMarginX;
        end;
      end;
    end;

    P := NextP;
  end;
  // went thru the whole line without finding the point,
  if not StartedDrawing then
    X := GetStartX( Style, Line );
end;

function TRichTextLayout.GetLineFromPosition( YToFind: longint;
                                              Var LineIndex: longint;
                                              Var Remainder: longint ): TTextPosition;
var
  Y: longint;
  LineHeight: longint;
begin
  LineIndex := 0;
  Remainder := 0;

  Y := FRichTextSettings.Margins.Top;

  if YToFind < Y then
  begin
    Result := tpAboveText;
    Exit;   //==>
  end;

  // TODO: Replace FNumLines with FLines.Count-1
  while LineIndex < FNumLines do
  begin
    LineHeight := FLines[LineIndex].Height;
    if     ( YToFind >= Y )
       and ( YToFind < (Y + LineHeight)) then
      begin
        // YToFind is within the line
        Result := tpWithinText;
        Remainder := YToFind - Y;
        exit;
      end;

    inc( Y, LineHeight );
    inc( LineIndex );
  end;

  LineIndex := FNumLines - 1;
  { check for a valid range }
  if (LineIndex < 0) or (LineIndex > FLines.Count-1) then
    Remainder := 0
  else
    Remainder := FLines[LineIndex].Height;

  Result := tpBelowText;
end;

function TRichTextLayout.FindPoint( XToFind, YToFind: longint;
                                    Var LineIndex: longint;
                                    Var Offset: longint;
                                    Var Link: string ): TTextPosition;
var
  Remainder: longint;
begin
  Link := '';
  Result := GetLineFromPosition(YToFind, LineIndex, Remainder);
  case Result of
    tpAboveText:
    begin
      Offset := 0;
      exit;
    end;

    tpBelowText:
    begin
      Offset := FLines[LineIndex].Length;
      exit;
    end;
  end;

  // found the line
  GetOffsetFromX( XToFind,
                  LineIndex,
                  Offset,
                  Link );
end;

function TRichTextLayout.GetLineFromCharIndex( Index: longint ): longint;
var
  LineCharIndex: longint;
  LineLength: longint;
begin
  Result := 0;
  if Index <= 0 then
    Exit;   //==>

  while Result < FNumLines do
  begin
    LineCharIndex := GetCharIndex(FLines[Result].Text );
    LineLength := FLines[Result].Length;
    if (LineCharIndex + LineLength) > Index then
    begin
      // found
      Exit; //==>
    end;
    inc( Result );
  end;
  Result := FNumLines - 1;
end;

function TRichTextLayout.GetOffsetFromCharIndex( Index: longint;
                                                 Line: longint ): longint;
begin
  Result := Index - GetCharIndex(FLines[Line].Text);
end;

function TRichTextLayout.GetElementWidth( Element: TTextElement ): longint;
var
  Bitmap: TfpgImage;
  BitmapIndex: longint;
begin
  // Now find out how wide the thing is
  case Element.ElementType of
    teImage:
    begin
      try
        BitmapIndex := StrToInt( Element.Tag.Arguments );
      except
        BitmapIndex := -1;
      end;
      if IsValidBitmapIndex( BitmapIndex ) then
      begin
        Bitmap := FImages.Items[BitmapIndex].Image;
        Result := Trunc(Bitmap.Width * FHorizontalImageScale);
      end;
    end;

    teText, teWordBreak:
      Result := FFontManager.CharWidth( Element.Character );

    else
      Assert( False ); // should never be trying to find the width of a style, etc

  end;
end;

Function TRichTextLayout.GetCharIndex( P: PChar ): longint;
begin
  Result := PCharDiff( P, FText );
end;

function TRichTextLayout.GetLinePosition( Line: longint ): longint;
begin
  Result := FRichTextSettings.Margins.Top;
  dec( line );
  while line >= 0 do
  begin
    inc( Result, Flines[Line].Height );
    dec( line );
  end;
end;

function TRichTextLayout.LinkFromIndex( const CharIndexToFind: longint): string;
Var
  P: PChar;
  NextP: PChar;
  EndP: PChar;
  Element: TTextElement;
  LineIndex: longint;
  Line: TLayoutLine;
begin
  if FNumLines = 0 then
  begin
    Result := '';
    Exit;   //==>
  end;

  LineIndex := GetLineFromCharIndex( CharIndexToFind );

  Line := FLines[LineIndex];
  P := Line.Text;
  EndP := Line.Text + Line.Length;

  if Line.LinkIndex <> -1 then
    Result := FLinks[ Line.LinkIndex ]
  else
    Result := '';

  while P < EndP do
  begin
    if GetCharIndex( P ) >= CharIndexToFind then
      exit;

    Element := ExtractNextTextElement( P, NextP );

    case Element.ElementType of
      teStyle:
        case Element.Tag.TagType of
          ttBeginLink:
            Result := Element.Tag.Arguments;
          ttEndLink:
            Result := '';
        end;
    end;

    P := NextP;
  end;
end;


end.