Delphi, VirtualStringTree - handling simple text styles (like bbcode)

what would be best way to handle simple text styles like bbcode allowing bold italic etc inside of the text? what I did is dividing the text into parts, each part has assigned style and then I textout each piece, starting from Rect.Left + Canvas.TextWidth(Texts[i-1]). This however is probably quite slow, moreover I have no idea how to text it out in case of VirtualStringTree. It has OnBeforeItemPaint but the callback is not aware of column index. The OnBeforeCellPaint however doesn't expose the variable to say VST I did painted on my own, therefore it paints on my text...

Anyone, please? :)

regards, Michal

I've done something similar using a simple subset of HTML tags. Here's the code to draw the text:

function TMyVST.DrawHTML(const ARect: TRect; const ACanvas: TCanvas; const Text: String): Integer;
(*DrawHTML - Draws text on a canvas using tags based on a simple subset of HTML/CSS

  <B> - Bold e.g. <B>This is bold</B>
  <I> - Italic e.g. <I>This is italic</I>
  <U> - Underline e.g. <U>This is underlined</U>
  <font-color=x> Font colour e.g.
                <font-color=clRed>Delphi red</font-color>
                <font-color=#FFFFFF>Web white</font-color>
                <font-color=$000000>Hex black</font-color>
  <font-size=x> Font size e.g. <font-size=30>This is some big text</font-size>
  <font-family> Font family e.g. <font-family=Arial>This is arial</font-family>*)

  function CloseTag(const ATag: String): String;
  begin
    Result := concat('/', ATag);
  end;

  function GetTagValue(const ATag: String): String;
  var
    p: Integer;
  begin
    p := pos('=', ATag);

    if p = 0 then
      Result := ''
    else
      Result := copy(ATag, p + 1, MaxInt);
  end;

  function ColorCodeToColor(const Value: String): TColor;
  var
    HexValue: String;
  begin
    Result := 0;

    if Value <> '' then
    begin
      if (length(Value) >= 2) and (copy(Uppercase(Value), 1, 2) = 'CL') then
      begin
        // Delphi colour
        Result := StringToColor(Value);
      end else
      if Value[1] = '#' then
      begin
        // Web colour
        HexValue := copy(Value, 2, 6);

        Result := RGB(StrToInt('$'+Copy(HexValue, 1, 2)),
                      StrToInt('$'+Copy(HexValue, 3, 2)),
                      StrToInt('$'+Copy(HexValue, 5, 2)));
      end
      else
        // Hex or decimal colour
        Result := StrToIntDef(Value, 0);
    end;
  end;

const
  TagBold = 'B';
  TagItalic = 'I';
  TagUnderline = 'U';
  TagBreak = 'BR';
  TagFontSize = 'FONT-SIZE';
  TagFontFamily = 'FONT-FAMILY';
  TagFontColour = 'FONT-COLOR';
  TagColour = 'COLOUR';

var
  x, y, idx, CharWidth, MaxCharHeight: Integer;
  CurrChar: Char;
  Tag, TagValue: String;
  PreviousFontColour: TColor;
  PreviousFontFamily: String;
  PreviousFontSize: Integer;
  PreviousColour: TColor;

begin
  ACanvas.Font.Size := Canvas.Font.Size;
  ACanvas.Font.Name := Canvas.Font.Name;
  ACanvas.Font.Color := Canvas.Font.Color;
  ACanvas.Font.Style := Canvas.Font.Style;

  PreviousFontColour := ACanvas.Font.Color;
  PreviousFontFamily := ACanvas.Font.Name;
  PreviousFontSize := ACanvas.Font.Size;
  PreviousColour := ACanvas.Brush.Color;

  x := ARect.Left;
  y := ARect.Top + 1;
  idx := 1;

  MaxCharHeight := ACanvas.TextHeight('Ag');

  While idx <= length(Text) do
  begin
    CurrChar := Text[idx];

    // Is this a tag?
    if CurrChar = '<' then
    begin
      Tag := '';

      inc(idx);

      // Find the end of then tag
      while (Text[idx] <> '>') and (idx <= length(Text)) do
      begin
        Tag := concat(Tag,  UpperCase(Text[idx]));

        inc(idx);
      end;

      ///////////////////////////////////////////////////
      // Simple tags
      ///////////////////////////////////////////////////
      if Tag = TagBold then
        ACanvas.Font.Style := ACanvas.Font.Style + [fsBold] else

      if Tag = TagItalic then
        ACanvas.Font.Style := ACanvas.Font.Style + [fsItalic] else

      if Tag = TagUnderline then
        ACanvas.Font.Style := ACanvas.Font.Style + [fsUnderline] else

      if Tag = TagBreak then
      begin
        x := ARect.Left;

        inc(y, MaxCharHeight);
      end else

      ///////////////////////////////////////////////////
      // Closing tags
      ///////////////////////////////////////////////////
      if Tag = CloseTag(TagBold) then
        ACanvas.Font.Style := ACanvas.Font.Style - [fsBold] else

      if Tag = CloseTag(TagItalic) then
        ACanvas.Font.Style := ACanvas.Font.Style - [fsItalic] else

      if Tag = CloseTag(TagUnderline) then
        ACanvas.Font.Style := ACanvas.Font.Style - [fsUnderline] else

      if Tag = CloseTag(TagFontSize) then
        ACanvas.Font.Size := PreviousFontSize else

      if Tag = CloseTag(TagFontFamily) then
        ACanvas.Font.Name := PreviousFontFamily else

      if Tag = CloseTag(TagFontColour) then
        ACanvas.Font.Color := PreviousFontColour else

      if Tag = CloseTag(TagColour) then
        ACanvas.Brush.Color := PreviousColour else

      ///////////////////////////////////////////////////
      // Tags with values
      ///////////////////////////////////////////////////
      begin
        // Get the tag value (everything after '=')
        TagValue := GetTagValue(Tag);

        if TagValue <> '' then
        begin
          // Remove the value from the tag
          Tag := copy(Tag, 1, pos('=', Tag) - 1);

          if Tag = TagFontSize then
          begin
            PreviousFontSize := ACanvas.Font.Size;
            ACanvas.Font.Size := StrToIntDef(TagValue, ACanvas.Font.Size);
          end else

          if Tag = TagFontFamily then
          begin
            PreviousFontFamily := ACanvas.Font.Name;
            ACanvas.Font.Name := TagValue;
          end;

          if Tag = TagFontColour then
          begin
            PreviousFontColour := ACanvas.Font.Color;

            try
              ACanvas.Font.Color := ColorCodeToColor(TagValue);
            except
              //Just in case the canvas colour is invalid
            end;
          end else

          if Tag = TagColour then
          begin
            PreviousColour := ACanvas.Brush.Color;

            try
              ACanvas.Brush.Color := ColorCodeToColor(TagValue);
            except
              //Just in case the canvas colour is invalid
            end;
          end;
        end;
      end;
    end
    else
    // Draw the character if it's not a ctrl char
    if CurrChar >= #32 then
    begin
      CharWidth := ACanvas.TextWidth(CurrChar);

      if x + CharWidth > ARect.Right then
      begin
        x := ARect.Left;

        inc(y, MaxCharHeight);
      end;

      if y + MaxCharHeight < ARect.Bottom then
      begin
        ACanvas.Brush.Style := bsClear;

        ACanvas.TextOut(x, y, CurrChar);
      end;

      x := x + CharWidth;
    end;

    inc(idx);
  end;

  Result := x;
end;

... and the DoAfterCellPaint call

procedure TMyVST.DoAfterCellPaint(Canvas: TCanvas;
  Node: PVirtualNode; Column: TColumnIndex; CellRect: TRect);
begin
  inherited;

  DrawHTML(CellRect, Canvas, 'HTML <B>tagged</B> string');
end;