Sometimes, I need to take action on only those lines visible within a
RichEdit control. The top line is easily retrieved using the GetFirstVisibleLine
message, whereas a combination of messages is required to get the bottom
line.

Primary Code:
The CharFromPos message is used to get the character at the bottom of
the client area of the RichEdit control. If there is no character there, then
CharFromPos returns the closest character - from which the LineFromChar
message can be used to get the bottom-most visible line#.

The great thing about CharFromPos is that it returns the nearest character,
even if that character is not directly under the specified position. So this
code works even when the last visible line in the control is not at the bottom
of the RichEdit control client area.

The code is provided below, and is also available in the
gbSnippets PowerBASIC source code library (snippet# gbs_00407).
You can get the entire library by downloading gbSnippets or you
can view individual snippets online.

gbSnippets home page: http://www.garybeene.com/sw/gbsnippets.htm
Online source code listings: http://www.garybeene.com/power/code/

If you've already installed gbSnippets, you can ensure that your local
library is synchronized with the latest snippets on the gbSnippets server
by using the "Actions/Synchronize with gbSnippets Server" menu.

Here's the basic code:
Code:
Sub GetTopBottomLines(iTopLine&, iBottomLine&)
    'assumes hDlg, %IDC_RichEdit and hRichEdit Global variables
    Local P as Point, w as Long, h as Long
    Control Get Client hDlg, %IDC_RichEdit TO w,h
    P.x = w : P.y = h
    iTopLine& = SendMessage(hRichEdit, %EM_GetFirstVisibleLine,0,0)       'visible line# at top of control
    iBottomLine& = SendMessage(hRichEdit, %EM_CharFromPos, 0, VarPTR(P) )
    iBottomLine& = SendMessage(hRichEdit, %EM_LineFromChar, iBottomLine&, 0)
End Sub
Compilable Example:
And here's a compilable example:
Code:
'Compilable Example:
#Compile Exe
#Dim All
#Include "Win32API.inc"
#Include "RichEdit.inc"
#Include "CommCtrl.inc"
Global hDlg as DWord, hRichEdit as DWord
%ID_RichEdit = 500
Function PBMain() As Long
   Local style&, buf$, i As Long
   For i = 0 To 40 : buf$ = buf$ + Str$(i) + "line" + $CrLf : Next i : buf$ = Trim$(buf$, $crlf)
   style& = %WS_Child Or %WS_Visible Or %ES_MultiLine Or %WS_VScroll Or %ES_AutoHScroll _
             Or %WS_HScroll Or %ES_AutoVScroll Or %ES_WantReturn Or %ES_NoHideSel Or %WS_TabStop
   Dialog New Pixels, 0, "Test Code",300,300,200,150, %WS_OverlappedWindow To hDlg
   Control Add Button, hDlg, 100,"Push", 30,10,140,20
   LoadLibrary("riched32.dll") : InitCommonControls
   Control Add "RichEdit", hDlg, %ID_RichEdit, buf$,20,40,160,100, style&, %WS_EX_ClientEdge
   Control Handle hDlg, %ID_RichEdit To hRichEdit
   Dialog Show Modal hDlg Call DlgProc
End Function
CallBack Function DlgProc() As Long
   Local iTopLine&, iBottomLine&, P as Point, w as Long, h as Long
   Select Case CB.Msg
      Case %WM_Command
         If CB.Ctl = 100 AND CB.Ctlmsg = %BN_Clicked Then 
            GetTopBottomLines(iTopLine&, iBottomLine&)        
            ? Str$(iTopLine&) + " : " + Str$(iBottomLine&)
         End If
      Case %WM_Size
         Dialog Get Client hDlg To w,h
         Control Set Size hDlg, %ID_RichEdit, w-40, h-60
   End Select
End Function

Sub GetTopBottomLines(iTopLine&, iBottomLine&)
    'assumes hDlg, %ID_RichEdit and hRichEdit Global variables
    Local P as Point, w as Long, h as Long
    Control Get Client hDlg, %ID_RichEdit TO w,h
    P.x = w : P.y = h
    iTopLine& = SendMessage(hRichEdit, %EM_GetFirstVisibleLine,0,0)       'visible line# at top of control
    iBottomLine& = SendMessage(hRichEdit, %EM_CharFromPos, 0, VarPTR(P) )
    iBottomLine& = SendMessage(hRichEdit, %EM_LineFromChar, iBottomLine&, 0)
End Sub    

'gbs_00407