RichEdit’s Nested Table Facility

One subject that seems to come up every other month or so is how RichEdit tables work. So I might as well post the answer. Hopefully RichEdit tables will eventually be described in the Windows SDK. They are not directly related to Math in Office, but I had mathematical expressions in mind when designing RichEdit’s table facility. Both mathematics and tables are recursive. For example you can have a fraction in the numerator of another fraction, and you can have a table in the cell of another table. So implementing tables seemed like a useful project that might also reveal how to implement a WYSIWYG implementation of mathematics. In fact, MathML <mtable>’s have a lot in common with general tables.

Most people at the time (1999) were recommending that a table cell should be represented by a whole RichEdit instance, which would give great generality. But I wanted a model that was much smaller, faster and worked with the built-in Find/Replace functionality and the RTF file converters. To this end, we needed a model, like Word’s, that was part of a single document instance, and could be overlaid on the existing paragraph structure. Accordingly RichEdit's table implementation is very efficient and fast, in fact, much faster than Word’s (although less general). Improvements have been made over the years, but the discussion that follows applies to RichEdit 4.0, which shipped with Office 2002, and RichEdit 4.1, which ships with Windows XP and Vista to this day. It also applies to later versions that ship with Office 2003 & 2007, which have additional features..

Specifically a cell containing a single line of text is represented only by that text, not by some larger structure. An empty cell consists of the single character, the cell mark U+0007. A cell containing multiple lines of text is expressed in terms of a structure that is substantially smaller than a complete edit instance, followed by the CELL mark. Tables can be nested up to 15 levels deep; higher nestings are represented by tab-delimited text. Cells can contain multiple paragraphs of any kind, e.g., bidirectional text, arbitrary tabs and alignments.

The Spring of 1999 was shortly after the Unicode Technical Committee added the U+FFF9..U+FFFB delimiter characters for describing ruby text in Japanese. These characters were available for more general use and seemed ideal for RichEdit’s internal table structure. This choice preceded the addition of the internal-use-only U+FDDO..U+FDEF characters that we use for mathematical structure characters, among other things.

In the (in-memory) backing store, a table row has the form

    {CR...}CR

 

where { stands for the Unicode STARTGROUP character U+FFF9, and CR is the ASCII Carriage Return character U+000D. The delimiter } stands for the Unicode ENDGROUP character U+FFFB and ... stands for a sequence of cells, each consisting of cell text terminated by the CELL mark U+0007. For example, a row with three empty cells has the plain text understructure U+FFF9 U+000D U+0007 U+0007 U+0007 U+FFFB U+000D. The start and end group character pairs are assigned identical PARAFORMAT2 information that describe the row and cell parameters. If rows with different parameters are needed, they may follow one another with appropriate PARAFORMAT2 parameters. A horizontally or vertically merged cell has two characters: NOTACHAR (0xFFFF) followed by CELL (0x7). Any text that appears in a merged cell is stored in the first cell of the set of merged cells.

 

One way to insert tables is to copy/paste tables from Word. RichEdit reads and writes table RTF. For more programmatic purposes, RichEdit 4.0 introduced the message EM_INSERTTABLE (WM_USER + 232), which acts similarly to EM_REPLACESEL but inserts one or more table rows with empty cells instead of plain text. Specifically it deletes the text (if any) currently selected by the selection and then inserts empty table row(s) with the row and cell parameters given by wparam and lparam, respectively, as defined below. It leaves the selection pointing to the start of the first cell in the first row. The client can then populate the table cells by pointing the selection at the various cell end marks and inserting and formatting the desired text. Such text can include nested table rows, etc. Since wparam and lparam point at row and cell parameter structures, this API isn't compatible with Visual Basic and can't be easily added to RichEdit’s object model TOM, although TOM2 does have a general set of table interfaces.

The TABLEROWPARMS and TABLECELLPARMS structures are defined as

typedef struct _tableRowParms

{ // EM_INSERTTABLE wparam is a (TABLEROWPARMS *)

    BYTE cbRow; // Count of bytes in this structure

    BYTE cbCell; // Count of bytes in TABLECELLPARMS

    BYTE cCell; // Count of cells

    BYTE cRow; // Count of rows

    LONG dxCellMargin; // Cell left/right margin (\trgaph)

    LONG dxIndent; // Row left (right if fRTL indent (similar to \trleft)

    LONG dyHeight; // Row height (\trrh)

    DWORD nAlignment:3; // Row alignment (like PARAFORMAT::bAlignment,

                            // \trql, trqr, \trqc)

    DWORD fRTL:1; // Display cells in RTL order (\rtlrow)

    DWORD fKeep:1; // Keep row together (\trkeep}

    DWORD fKeepFollow:1; // Keep row on same page as following row (\trkeepfollow)

    DWORD fWrap:1; // Wrap text to right/left (depending on bAlignment)

                           // (see \tdfrmtxtLeftN, \tdfrmtxtRightN)

    DWORD fIdentCells:1; // lparam points at single struct valid for all cells

} TABLEROWPARMS;

typedef struct _tableCellParms

{ // EM_INSERTTABLE lparam is a (TABLECELLPARMS *)

    LONG dxWidth; // Cell width (\cellx)

    WORD nVertAlign:2; // Vertical alignment (0/1/2 = top/center/bottom

                            // \clvertalt (def), \clvertalc, \clvertalb)

    WORD fMergeTop:1; // Top cell for vertical merge (\clvmgf)

    WORD fMergePrev:1; // Merge with cell above (\clvmrg)

    WORD fVertical:1; // Display text top to bottom, right to left (\cltxtbrlv)

    WORD wShading; // Shading in .01% (\clshdng) e.g., 10000 flips fore/back

    SHORT dxBrdrLeft; // Left border width (\clbrdrl\brdrwN) (in twips)

    SHORT dyBrdrTop; // Top border width (\clbrdrt\brdrwN)

    SHORT dxBrdrRight; // Right border width (\clbrdrr\brdrwN)

    SHORT dyBrdrBottom; // Bottom border width (\clbrdrb\brdrwN)

    COLORREF crBrdrLeft; // Left border color (\clbrdrl\brdrcf)

    COLORREF crBrdrTop; // Top border color (\clbrdrt\brdrcf)

    COLORREF crBrdrRight; // Right border color (\clbrdrr\brdrcf)

    COLORREF crBrdrBottom; // Bottom border color (\clbrdrb\brdrcf)

    COLORREF crBackPat; // Background color (\clcbpat)

    COLORREF crForePat; // Foreground color (\clcfpat)

} TABLECELLPARMS;

Note that paragraph-format information containing the TABLEROWPARMS and TABLECELLPARMS information is attached to the table-row delimiters as set up by the EM_ INSERTTABLE message, so merely duplicating the plain-text table structure in the backing store isn't enough to insert a working table. In fact, methods like ITextRange::SetText() convert the special delimiters U+FFF9.U+FFFB to spaces (U+0020). Note also that this table structure is nestable.

The definition of EM_INSERTTABLE is extensible, since in the future we'll probably have to support more parameters for table rows and cells. The API also inserts a consistent table row all at once, so that no illegal table parts are present on return. Hence if the document is saved after such an insertion, valid Word-compatible RTF will be written. lparam points at the TABLECELLPARMS structure for the first cell in an array of TABLECELLPARMS structures. It's important that cbCell = sizeof(TABLECELLPARMS). That way RichEdit knows how much cell information the client is specifying. In particular, in the future if more cell parameters are defined, older clients can get away with specifying less and the new RichEdit can assign default values for the new parameters. Similarly cbRow says how many bytes are defined by the client for TABLEROWPARMS, in case RichEdit is revised to support more row parameters that the client doesn't know about.

To make simple tables easier to define, if fIdenticalCells = 1, lparam points at a single TABLECELLPARMS structure that is valid for all cells in the row. Note that a nonzero cell border width is guaranteed to give at least a one-pixel border.

The colors are limited to the standard 16 colors defined by

      RGB( 0, 0, 0), // \red0\green0\blue0

      RGB( 0, 0, 255), // \red0\green0\blue255

      RGB( 0, 255, 255), // \red0\green255\blue255

      RGB( 0, 255, 0), // \red0\green255\blue0

      RGB(255, 0, 255), // \red255\green0\blue255

      RGB(255, 0, 0), // \red255\green0\blue0

      RGB(255, 255, 0), // \red255\green255\blue0

      RGB(255, 255, 255), // \red255\green255\blue255

      RGB( 0, 0, 128), // \red0\green0\blue128

      RGB( 0, 128, 128), // \red0\green128\blue128

      RGB( 0, 128, 0), // \red0\green128\blue0

      RGB(128, 0, 128), // \red128\green0\blue128

      RGB(128, 0, 0), // \red128\green0\blue0

      RGB(128, 128, 0), // \red128\green128\blue0

      RGB(128, 128, 128), // \red128\green128\blue128

      RGB(192, 192, 192), // \red192\green192\blue192

plus two custom colors. The border widths are limited to the range 0 to 255 twips.

If the color index is not in the range 1..18, then autocolor is used, which usually ends up being the system Text or Background colors.

Comments

• Anonymous
  September 15, 2008
  The comment has been removed

• Anonymous
  September 25, 2008
  After a bit of experimentation, it turns out that the message is WM_USER+232. The following code snippet works for me, inserting a 3x2 table. Neat :) TABLEROWPARMS rows; ZeroMemory(&rows,sizeof rows); rows.cbRow = sizeof (TABLEROWPARMS); rows.cbCell = sizeof (TABLECELLPARMS); rows.cCell = 3; rows.cRow = 2; rows.dxCellMargin = 50; rows.nAlignment = 1; rows.dyHeight = 400; rows.fIdentCells = 1; TABLECELLPARMS cells; ZeroMemory(&cells,sizeof cells); cells.dxWidth = 1000; cells.dxBrdrLeft = 1; cells.dyBrdrTop = 1; cells.dxBrdrRight = 1; cells.dyBrdrBottom = 1; cells.crBackPat = RGB(255,255,255); cells.crForePat = RGB(0,0,0); SendMessage(richHwnd,WM_USER+232,(WPARAM)&rows,(LPARAM)&cells);

• Anonymous
  September 25, 2008
  Please, could you tell when more info about RichEdit weill be posted? I mean messages' numeric values, table definitions and etc.

• Anonymous
  September 30, 2008
  Yes! I agree with Alex! I mean messages values (WM_INSERTTABLEROW)!

• Anonymous
  October 03, 2008
  I was playing around with David's code above and found that if you set rows.fIdentCells = 0 and then pass in a pointer to an array of N TABLECELLPARMS structures where N is the number of columns in the table, you can set the style of individual columns with a single EM_INSERTTABLEROW message.   I'm not sure how to set up individual rows to be different, or to have different types of cells.  Murray, are there any style setting messages for tables?

• Anonymous
  October 03, 2008
  Actually, I did find out how to make rows different -- insert a table and then insert another table with a new style, or geometry, right below the first one.  With the second table, set the fMergeTop and fMergePrev members to 1, and the new table will attach itself to the first table -- pretty cool!

• Anonymous
  October 05, 2008
  Tom: Ah, I hadn't figured out how to get that working. Excellent!

• Anonymous
  November 21, 2008
  What paragraphs are and how they are formatted are questions that continually come up both inside and

• Anonymous
  December 16, 2008
  One observation using msftedit 5.41.15.1515 (XP SP3): Test states "Specifically it deletes the text (if any) currently selected by the selection" but EM_INSERTTABLEROW throws an error (0x80004005) if you try to replace a selection. Is it only possible to use EM_INSERTTABLEROW on a degenerated selection. It is nice to insert tables in this way, but as long as there are no messages to manipulate rows and cells attributes later on. So if there are notifications or messages please tell.

• Anonymous
  December 18, 2008
  My alternate code for row insertion (C++). Run successfully bool RTFTableSupport::InsertRow(const HWND hwndRE) { ASSERT(IsWindow(hwndRE)); CHARRANGE cr; SendMessage(hwndRE,EM_EXGETSEL,0,(LPARAM)&cr); CComPtr<ITextRange> Range=CTomUtil::GetITextRange(hwndRE,cr); ASSERT(Range); if (!Range) return false; Range->SetStart(cr.cpMin); const HRESULT hr=Range->EndOf(tomRow,tomMove,NULL); if (S_OK==hr) { Range->GetEnd(&cr.cpMax); cr.cpMax-=2; cr.cpMin=cr.cpMax; SendMessage(hwndRE,EM_EXSETSEL,0,(LPARAM)&cr); SendMessage(hwndRE,WM_KEYDOWN,VK_RETURN,0); SendMessage(hwndRE,WM_KEYUP,VK_RETURN,0); } return (S_OK == hr); }

• Anonymous
  February 01, 2009
  Hi  Carc, can you please specify your use of the TOM ? I didn't find anything on the net of your usage CTomUtil::GetITextRange() I'm very much interested in table insertions in richedit controls. Thanks, Stev

• Anonymous
  February 02, 2009
  You all are solving varous problems quite ably. The table facility in RE 41 is fairly limited with regard to resizing, but you can insert rows by inserting CR (U+000D) when the insertion point is displayed at the end of the table (actually the insertion point is in between the final CELL mark and the table row end delimiter <U+FFFB U+000D>. The table rows do resize automatically in the vertical direction. You can get an ITextRange from an ITextDocument as is documented in the SDK. But ITextRange has very limited support for tables. I'm hoping we can satisfy your requests for better RichEdit documentation and functionality in Windows. But it takes time, partly because of the extensive testing required by security concerns.

• Anonymous
  February 02, 2009
  Hi, Stev. Sorry for the my short code sample. I use TOM (Text Object Model) very ofter. And I develome helper module for getting interface of TOM. This may be write e.g //getting ITextDocument interface from RichEdit (hwnd of RichEdit) ITextDocument* PlugTomUtil::GetDocument(const HWND hwnd) { IUnknown* pOle=NULL; if (!SendMessage(hwnd,EM_GETOLEINTERFACE,0,(LPARAM)&pOle)) return NULL; ITextDocument* pDoc=NULL; const HRESULT hr=pOle->QueryInterface(IID_ITextDocument,(void**)&pDoc); pOle->Release(); return (S_OK == hr ? pDoc : NULL); } and later ITextDocument* pDoc=PlugTomUtil::GetDocument(hwndRichEdit); ITextRange* pRange=NULL; pDoc->Range(begin_of_range_position,end_of_range_position,&pRange); ...

• Anonymous
  February 03, 2009
  2Murray

1. I use TOM for insertion CR symbols only at code way.
2. How to move table columns size (or rows) at mouse? (RichEdit 5.0, XP SP3). How to implement the feature?

• Anonymous
  February 03, 2009
  RichEdit 6.0 lets one resize table columns and rows by dragging column and row borders with the mouse, as in Word. This functionality isn't exposed programmatically yet, but the methods to handle it are part of TOM2. It isn't worth defining the methods, since they haven't been implemented to date.

• Anonymous
  February 03, 2009
  Thank You! Where get RichEdit 6.0 DLL? The DLL available in Windows XP?

• Anonymous
  February 03, 2009
  The earlier post "Some RichEdit History" http://blogs.msdn.com/murrays/archive/2006/10/20/some-richedit-history.aspx describes how RichEdit 6.0 has been shipped. Basically it's part of Office 2007.

• Anonymous
  February 03, 2009
  I can use RichEdit 6.0 from VC code? My application use detection algorithm for RichEdit version "on fly". If available - use "RICHEDIT50W", other "RichEdit20W", other "RICHEDIT" class name. How use window class name for RichEdit 6.0?

• Anonymous
  February 04, 2009
  How to disable Clear Type font method for RichEdit fonts?

• Anonymous
  March 12, 2009
  How do I specify a transparent color of the table cells?