mapping fixed font to pixels

[Chris Holbrook]

Working on my hexdump application, which draws a page of hex data using a fixed font (Courier New), I wanted to ignore clicks on the whitespace between the columns. The character spacing is fixed, so asking Windows for the horizontal size, rather than using a number which seemed to fit my console, seemed like a good idea. However, the character size returned by GetTextMetrics is too small, and GetTextCharacterExtra returns zero.

my question is: is there a reliable way of predicting the pixel position of fixed-font text, and if so, what is it?

here's a compileable example, click on the data part of the display and metrics appear in the dialog caption.

' Does GetTextMetrics lie?
' to investigate mapping pixel positions to characters displayed in a LABEL
' Chris Holbrook Sep 2008
'
#COMPILE EXE
#DIM ALL
#INCLUDE "WIN32API.INC"
%IDD_DIALOG1 =  101
%IDC_LABEL1  = 1001

'----------------------------------------------------------------------
FUNCTION MakeFont(BYVAL fName AS STRING, BYVAL ptSize AS LONG, _
                  OPT BYVAL attr AS STRING) AS DWORD
   '--------------------------------------------------------------------
   ' Create a desired font and return its handle.
   ' attr = "biu" for bold, italic, and underlined (any order)
   '--------------------------------------------------------------------
   LOCAL hDC AS DWORD, CharSet AS LONG, CyPixels AS LONG
   LOCAL BOLD, italic, uLine AS LONG
    LOCAL tm AS TEXTMETRIC
   IF LEN(attr) THEN
      IF INSTR(LCASE$(attr), "b") THEN BOLD = %FW_BOLD
      IF INSTR(LCASE$(attr), "i") THEN italic = 1
      IF INSTR(LCASE$(attr), "u") THEN uLine = 1
   END IF
   hDC = GetDC(%HWND_DESKTOP)
   CyPixels  = GetDeviceCaps(hDC, %LOGPIXELSY)
   ReleaseDC %HWND_DESKTOP, hDC
   PtSize = 0 - (ptSize * CyPixels) \ 72
   FUNCTION = CreateFont(ptSize, 0, 0, 0, BOLD, italic, uLine, _
             %FALSE, CharSet, %OUT_TT_PRECIS, _
             %CLIP_DEFAULT_PRECIS, %DEFAULT_QUALITY, _
             %FF_MODERN , BYCOPY fName)
END FUNCTION
'-------------------------------------------------------------------------
CALLBACK FUNCTION ShowDIALOG1Proc()
    LOCAL s, stopline AS STRING
    LOCAL i, j, l, x, y, row, col AS LONG
    LOCAL ppage AS DWORD
    LOCAL q AS BYTE PTR
    LOCAL buffer AS STRING
    LOCAL pt AS POINTAPI
    LOCAL hFont, lcolor AS DWORD
    LOCAL tm AS TEXTMETRIC
    STATIC charwidth, rowheight AS LONG
    LOCAL hdc AS DWORD
    LOCAL m AS LONG
    

    SELECT CASE AS LONG CBMSG
        CASE %WM_INITDIALOG
            FOR i = 1 TO 256
                buffer = buffer + CHR$(i)
            NEXT
            ppage = STRPTR(buffer)
            hDC = getDC(getdlgitem(CBHNDL,%IDC_LABEL1))
            GetTextmetrics hDc, tm
            rowheight = tm.tmheight
            LOCAL intercharspace AS LONG
            intercharspace = GetTextCharacterExtra ( hdc)
            charwidth = tm.tmAveCharWidth + intercharspace'its a fixed font, so all chars should have the same width
            GOSUB drawlabel

        CASE %WM_LBUTTONDOWN
            pt.X = LO(WORD,CBLPARAM): pt.Y = HI(WORD,CBLPARAM)
            X = pt.X - (11*charwidth)
            ' 11 characters precede the data block but this only gets us to char 10!
            ' try to work out if click was on whitespace or on a value
            m = x MOD (3*charwidth)
            col = x \ 3*charwidth ' assume first char width in 3-char column is a space
            IF m > charwidth THEN
                 DIALOG SET TEXT CBHNDL, "charwidth =" + STR$(charwidth) + _
                                         " pos in row =" + STR$(x) + _
                                         " pos in block =" + STR$(m) + _
                                         " column = " + STR$(col)
            ELSE
                DIALOG SET TEXT CBHNDL, SPACE$(100)
            END IF
            row = (pt.Y - (2*rowheight)) \ rowheight

    END SELECT
    EXIT FUNCTION
drawlabel:
    s = STRING$(80 * 16, $SPC)
    FOR i = 0 TO 15
        FOR j = 0 TO 15
            q = ppage + (i*16) + j
            MID$(s, (i * 80) + (j*3)+ 10, 2) = HEX$(@q,2)
            IF INSTR ( "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"" £$%^&*()_+{}[]:@~;'#,./\<>?`¬",CHR$(@q)) <> 0 THEN
                MID$(s, (i * 80) + 59 + j, 1) = CHR$(@q)
            ELSE
                MID$(s, (i * 80) + 59 + j, 1) = "."
            END IF
        NEXT
        MID$(s, ((i) * 80) + 1, 11) = HEX$(ppage + i*16, 8)
        MID$(s, ((i + 1) * 80) -2, 2) = $CRLF
    NEXT
    stopline = SPACE$(11)
    FOR i = 0 TO 15
        stopline = stopline + HEX$(((ppage AND &HF) + i ) AND &HF)+ "  "
    NEXT
    s = stopline + _
        $CRLF + STRING$(57,"-") + "  " + STRING$(16,"-") + $CRLF + " " + s
    CONTROL SET TEXT CBHNDL, %idc_label1,  s
    RETURN
END FUNCTION
'-------------------------------------------------------------------------------
FUNCTION ShowDIALOG1(BYVAL hParent AS DWORD) AS LONG
    LOCAL lRslt AS LONG

    LOCAL hDlg   AS DWORD
    LOCAL hFont1 AS DWORD

    DIALOG NEW hParent, "character and pixel positioning                             Chris Holbrook Sep 2008", _
        70, 70, 430, 207, _
        %WS_POPUP OR %WS_BORDER OR _
        %WS_DLGFRAME OR %WS_SYSMENU OR %WS_CLIPSIBLINGS OR %WS_VISIBLE OR _
        %DS_MODALFRAME OR %DS_3DLOOK OR %DS_NOFAILCREATE OR %DS_SETFONT, _
        %WS_EX_CONTROLPARENT OR %WS_EX_LEFT OR %WS_EX_LTRREADING OR %WS_EX_RIGHTSCROLLBAR, TO hDlg
    CONTROL ADD LABEL, hDlg, %IDC_LABEL1, "", _
        5, 5, 420, 200, _
        %WS_CHILD OR %WS_VISIBLE 'OR %SS_NOWORDWRAP

    hFont1 = makefont("Courier New",10)
    CONTROL SEND hDlg, %IDC_LABEL1, %WM_SETFONT, hFont1, 0
    DIALOG SHOW MODAL hDlg, CALL ShowDIALOG1Proc TO lRslt
    DeleteObject hFont1
    FUNCTION = lRslt
END FUNCTION
'------------------------------------------------------------
FUNCTION PBMAIN()
    ShowDIALOG1 %HWND_DESKTOP
END FUNCTION

[Chris Holbrook]

Forget the above, an array of 256 labels works much better.