I thought I'd write this up after jumping through all kinds of hoops to make this work.
I needed to know the line spacing in a RichEdit control. Reason was I'm implementing line #s in my editor (EdAsm, described elsewhere here). I needed the line spacing so the line #s would align with the lines of text in the control.
I tried 3 methods, none of which worked correctly:
- Using GetTextMetrics() on the edit control's device context, and using the values returned (tmHeight, tmAscent, tmInternalLeading). No combination of these worked.
- Using the line-spacing values from the PARAFORMAT2 structure, returned by EM_GETPARAFORMAT for RichEdit controls. Not only did this not work, I found out that this whole method is screwed up and doesn't work as advertised by Micro$oft.
- The method used by Ketil0 in his line-numbering scheme (which does work for him, apparently), that uses GetTextExtentPoint32() on a buffer with 4 "W"s in it.
These methods came close (but no cigar, as they say): the line #s simply didn't line up with the control text.
I exchanged some PMs with JJ, who suggested I try EM_LINEINDEX and EM_POSFROMCHAR. At first I didn't see how this could possibly help me, but after scratching my head it dawned on me: assuming your edit control has at least 2 lines of text in it, you find one line of text in the control, get the y-coordinate of the 1st character on the line, do the same for the next line of text, subtract the 2 y-coords., and bingo, there's your line spacing.
It works. But wait a second: what if your edit control is empty? Doesn't work because there ain't no text in it. So I came up with a somewhat ugly but valid work-around: if the edit control has fewer than 2 lines of text in it, I
- Save the "modified" status of the control
- Extract the text, if any, from the control and store in a buffer
- Plug in dummy text consisting of 2 lines of text ("x", CR/LF, "x")
- Measure the line spacing as described above
- Restore the original text, if any
- Restore the original "modified" status
This all works well. Here's the code, including all the "doesn't work" code:
LineSpacingMeasureTxt DB "x", $CRLF, "x", 0 ;Two lines of text.
;====================================
; GetEditLineHeight()
;
; Gets the line height of the current edit font.
;====================================
GetEditLineHeight PROC
LOCAL pt:POINTL, dummyTextFlag:DWORD, modifyFlag:DWORD, buffer[1024]:BYTE
MOV dummyTextFlag, FALSE
INVOKE SendMessage, EditHandle, EM_GETLINECOUNT, 0, 0
CMP EAX, 2 ;At least 2 lines?
JAE enough
; One or no lines in control: extract text from control, add 2 dummy lines,
; measure line spacing, then replace existing text:
INVOKE SendMessage, EditHandle, EM_GETMODIFY, 0, 0
MOV modifyFlag, EAX
INVOKE GetWindowText, EditHandle, ADDR buffer, SIZEOF buffer
INVOKE SetWindowText, EditHandle, OFFSET LineSpacingMeasureTxt
MOV dummyTextFlag, TRUE
;***** This method works, but requires at least 2 lines of text in the control: *****
enough: INVOKE SendMessage, EditHandle, EM_LINEINDEX, 1, 0 ;Line 2.
INVOKE SendMessage, EditHandle, EM_POSFROMCHAR, ADDR pt, EAX
MOV EAX, pt.y
MOV EditLineHeight, EAX
INVOKE SendMessage, EditHandle, EM_LINEINDEX, 0, 0 ;Line 1.
INVOKE SendMessage, EditHandle, EM_POSFROMCHAR, ADDR pt, EAX
MOV EAX, pt.y
SUB EditLineHeight, EAX
; See if we need to remove dummy text:
CMP dummyTextFlag, TRUE
JNE @F
INVOKE SetWindowText, EditHandle, ADDR buffer
INVOKE SendMessage, EM_SETMODIFY, EditHandle, modifyFlag, 0
@@: RET
;***** DOESN'T WORK! *****
; INVOKE GetDC, EditHandle
; MOV hDC, EAX
; INVOKE GetTextMetrics, hDC, ADDR tm
; MOV EAX, tm.tmInternalLeading
; MOV EAX, tm.tmHeight
; SUB EAX, tm.tmInternalLeading
; MOV EditLineHeight, EAX
; INVOKE ReleaseDC, EditHandle, hDC
; From MSDN (https://learn.microsoft.com/en-us/windows/win32/controls/em-getparaformat):
;***** DOESN'T WORK! *****
; MOV pf2.cbSize, SIZEOF PARAFORMAT2
; MOV pf2.dwMask, PFM_LINESPACING
; MOV pf2.bLineSpacingRule, 2 ;Set spacing as twips/20.
; MOV pf2.dyLineSpacing, 30
; INVOKE SendMessage, EditHandle, EM_SETPARAFORMAT, 0, ADDR pf2
; MOV pf2.bLineSpacingRule, 4 ;Get spacing in twips.
; INVOKE SendMessage, EditHandle, EM_GETPARAFORMAT, 0, ADDR pf2
; MOV EAX, pf2.dyLineSpacing
; MOV EditLineHeight, EAX
; invoke wsprintf, addr buffer, offset lsfmt, EditLineHeight
; invoke MessageBox, NULL, addr buffer, NULL, MB_OK
; Ketil0's method:
;***** DOESN'T WORK! *****
; MOV EAX, 'WWWW'
; MOV DWORD PTR buffer, EAX
; INVOKE GetTextExtentPoint32, hDC, ADDR buffer, 4, ADDR pt
; MOV EAX, pt.y
; MOV EditLineHeight, EAX
GetEditLineHeight ENDP