Author: Jonas Bilinkevicius

How to detect a mouse movement over a word in a TRichEdit

Answer:

Solve 1:

How can I detect when the mouse runs over a word or an expression in a TRichEdit?

You start by adding a handler to the TRichEdit's OnMouseMove event. In the handler 
you get to the character under the mouse with:

1   uses
2     richedit; {for EM_EXLINEFROMCHAR}
3   
4   var
5     pt: TPoint;
6     charindex, lineindex, charoffset: Integer;
7   begin
8     pt := Point(X, Y);
9     charindex := richedit.perform(Messages.EM_CHARFROMPOS, 0, integer(@pt));
10    if charindex >= 0 then
11    begin
12      lineindex := richedit.perform(EM_EXLINEFROMCHAR, 0, charindex);
13      charoffset := charindex - richedit.perform(EM_LINEINDEX, lineindex, 0);
14    end;
15  end;


Lineindex and charoffset now allow you to get the line out of the richedit.Lines 
array and look at the characters value. Note that you have to use charoffset+1 as 
index into the string, e.g.:

16  S := richedit.lines[lineindex];
17  charundercursor := S[charoffset + 1];


If charundercursor is a letter (IsCharAlpha( charundercursor )) you could now walk 
backwards in S to find the start of the word and forward to find its end. Similar 
for an "expression" (whatever that may mean in your context).


Solve 2:

Using the source code above, how can I determine, whether the mouse is over a 
phrase like 'Inprise Delphi', which has the text attribute Bold and the colour Lime?

Well, you have to jump through some hoops, I'm afraid. The TRichEdit component has 
a method FindText that can be used to search for text, ignoring any text 
attributes. It would go something like this:

18  {additional vars required}
19  S: string;
20  foundPos, oldSelStart: Integer;
21  
22  {after determining charindex as above}
23  S := 'Inprise Delphi'; {text to search for}
24  foundpos := richedit.FindText(S, charindex - Length(S) + 1, charindex + Length(S),
25    [stWholeWord, stMatchCase]);
26  if foundpos > = 0 then
27  begin
28    {found the text, check attributes}
29    {for this we need to select the text}
30    oldSelStart := richedit.SelStart;
31    richedit.SelStart := foundPos;
32    richedit.SelLength := Length(S);
33    with richedit.SelAttributes do
34      if ((ConsistentAttributes * [caBold, caColor]) = [caBold, caColor]) and
35        (Color = clLime) and (fsBold in Style) then
36        {we have a match!}
37      else
38        SelStart := oldSelStart;
39  end;



Solve 3:

How can I tell from a WM_MOUSEMOVE message that the mouse cursor is over a 
particular character or line of a TRichedit? I am simulating a very simplistic 
browser and want to know when the user is over a "hyperlink" which is really just a 
TRichedit with some of the text underlined. That way I can tell the cursor to 
change from crHand and back.

40  uses
41    richedit;
42  
43  var
44    pt: TPoint;
45    charindex, row, col: Integer;
46  
47  { ... }
48  GetCursorPos(pt);
49  pt := richedit.screentoclient(pt);
50  charindex := richedit1.perform(Messages.EM_CHARFROMPOS, 0, integer(@pt));
51  Row := richedit1.PerForm(EM_EXLINEFROMCHAR, 0, charindex);
52  Col := charindex - richedit1.Perform(EM_LINEINDEX, Row, 0);


Solve 4:

Looking for a way to find the character position the mouse is over during a 
TRichEdit.onMouseMove event.

53  var
54    msg: TMessage;
55    pt: TPoint;
56    pos: integer; {offset into RichEdit.Text}
57  
58  { ... }
59  pt.x := X;
60  pt.y := Y;
61  msg.Result := SendMessage(RichEdit.handle, EM_CHarFromPos, 0, Integer(@pt));
62  pos := msg.ResultLo;
63  if RichEdit.Text[pos] = '?' then
64    { ... }