As Chris surmised, 'StretchDIBits' is required for Vista. I had to change only the following callback function to incorporate that API. I'm embarrassed to admit how many hours I required getting there, even making heavy use of Poffs2, and for that reason, I thought others might benefit from the code.
Code:
TYPE MyBITMAPINFO
bmiHeader AS BITMAPINFOHEADER
bmiColors(0 TO 1) AS RGBQUAD
END TYPE
CALLBACK FUNCTION printPreviewProc()
LOCAL hdc AS DWORD, xppi, yppi, hPrnDC, hOldBmp, result AS LONG
LOCAL ps AS PAINTSTRUCT, s AS STRING, wi, ht AS SINGLE
STATIC bm AS BITMAP 'bitmap of rich edit page
STATIC bmBits AS STRING 'string serving as memory for DIB bits
STATIC bmSize AS LONG 'space needed by bitmap bits
STATIC bmInfo AS myBITMAPINFO 'structure defining properties of a DIB
STATIC bitsPtr AS STRING PTR 'pointer to string memory
STATIC nWi, nHt, nx, ny, xp, yp, x, y, kx, ky AS DWORD
STATIC nPage, numPages, dPages, lastPage, hVScroll, hHScroll AS LONG
STATIC memdc, hBmp AS DWORD, zoom AS SINGLE, si, ssi AS SCROLLINFO, r AS rect
SELECT CASE CBMSG
CASE %WM_INITDIALOG
'create window that proportionally matches printed paper
'with hidden scrollbars for zoom feature
IF PRINTERCOUNT = 0 THEN
MSGBOX "No windows printers are connected", %MB_ICONERROR, "Initialize Print Preview"
DIALOG END CBHNDL: EXIT FUNCTION
END IF
XPRINT ATTACH DEFAULT
XPRINT GET CLIENT TO wi, ht
XPRINT GET DC TO hPrnDC
hdc = GetDC(CBHNDL)
xppi = GetDeviceCaps(hdc, %LOGPIXELSX)
yppi = GetDeviceCaps(hdc, %LOGPIXELSY)
nHt = .90 * GetDeviceCaps(hdc, %VERTRES) - 90
nWi = (wi/ht) * (xppi / yppi) * nHt
x = MAX(460, nWi + 60)
DIALOG SET CLIENT CBHNDL, x, nHt + 60
DIALOG SET LOC CBHNDL, 100, 10
nx = (x - nWi - 9)/2: ny = 30
CONTROL SET SIZE CBHNDL, %IDC_VScroll, 18, nHt
CONTROL SET LOC CBHNDL, %IDC_VScroll, nx + nWi, ny
CONTROL SET SIZE CBHNDL, %IDC_HScroll, nWi, 18
CONTROL SET LOC CBHNDL, %IDC_HScroll, nx, nHt + ny
CONTROL SHOW STATE CBHNDL, %IDC_VScroll, %SW_HIDE
CONTROL SHOW STATE CBHNDL, %IDC_HScroll, %SW_HIDE
CONTROL HANDLE CBHNDL, %IDC_VScroll TO hVScroll
CONTROL HANDLE CBHNDL, %IDC_HScroll TO hHScroll
memdc = CreateCompatibleDC(hPrnDC)
hBmp = CreateCompatibleBitmap(hPrnDC, wi, ht)
SelectObject memdc, hBmp
'initialize info for DIB (device independent bitmap)
bmInfo.bmiHeader.biSize = SIZEOF(bmInfo.bmiHeader)
bmInfo.bmiHeader.biWidth = wi
bmInfo.bmiHeader.biHeight = ht
bmInfo.bmiHeader.biPlanes = 1
bmInfo.bmiHeader.biBitCount = 1 'monochrome
bmInfo.bmiHeader.biCompression = %BI_RGB
bmInfo.bmiColors(0).rgbBlue = 255
bmInfo.bmiColors(0).rgbGreen = 255
bmInfo.bmiColors(0).rgbRed = 255
bmInfo.bmiColors(1).rgbBlue = 0
bmInfo.bmiColors(1).rgbGreen = 0
bmInfo.bmiColors(1).rgbRed = 0
'create string for DIB memory space [bmBits]
'and calculate size needed it [bmSize]
bmBits = STRING$(SIZEOF(BITMAPINFOHEADER), 0)
bmSize = wi
bmSize = (bmSize + 1) / 8
bmSize = ((bmSize + 3) / 4) * 4
bmSize = bmSize * ht
bmBits = bmBits + STRING$(bmSize, 0)
bitsPtr = STRPTR(bmbits) + SIZEOF(BITMAPINFOHEADER)
'initialize top controls for specifying pages to preview
xp = wi: yp = ht: zoom = 1: x = 0: y = 0
numPages = printRTF(hPrnDC, -1, 0, -1)
IF numPages THEN
nPage = 1: CONTROL SET TEXT CBHNDL, %IDC_PageNo, " 1": GOSUB previewPage
END IF
dPages = MAX(numPages / 10, 5)
r.nLeft = nx: r.nTop = ny
r.nRight = r.nLeft + nWi: r.nBottom = r.nTop + nHt
CONTROL SET TEXT CBHNDL, %IDC_NumPages, "of" + STR$(numPages) + " pages"
CONTROL SEND CBHNDL, %IDC_PageNo, %EM_SETSEL, -1, 0
CONTROL SET FOCUS CBHNDL, %IDC_PageNo
CASE %WM_PAINT
hdc = BeginPaint(CBHNDL, ps)
result = StretchDIBits(hdc, nx, ny, nWi, nHt, x, y, xp/zoom, yp/zoom, _
BYVAL bitsPtr, BYVAL VARPTR(bmInfo), %DIB_RGB_COLORS, %SRCCOPY)
EndPaint CBHNDL, ps
CASE %WM_COMMAND
IF CBCTL = %IDC_Fwd THEN
IF nPage < numPages THEN INCR nPage: GOSUB previewPage
ELSEIF CBCTL = %IDC_Bwd THEN
IF nPage > 1 THEN DECR nPage: GOSUB previewPage
ELSEIF CBCTL = %IDC_FastFwd THEN
nPage = MIN(nPage + dPages, numPages)
IF nPage <> lastPage THEN GOSUB previewPage
ELSEIF CBCTL = %IDC_FastBwd THEN
nPage = MAX(nPage - dPages, 1)
IF nPage <> lastPage THEN GOSUB previewPage
ELSEIF CBCTL = %IDOK THEN 'clicked ENTER key
CONTROL GET TEXT CBHNDL, %IDC_PageNo TO s
IF VAL(s) THEN
nPage = MAX(1, MIN(VAL(s), numPages))
CONTROL SET TEXT CBHNDL, %IDC_PageNo, STR$(nPage)
IF nPage <> lastPage THEN
lastPage = nPage: zoom = 2.25
GOSUB previewPage
END IF
END IF
ELSEIF CBCTL = %IDCANCEL THEN 'clicked ESC key
DIALOG END CBHNDL
ELSEIF CBCTL = %IDC_Zoom THEN
zoom = 1.5 * zoom: IF zoom > 2.25 THEN zoom = 1
IF zoom > 1 THEN
CONTROL SHOW STATE CBHNDL, %IDC_VScroll, %SW_SHOW
CONTROL SHOW STATE CBHNDL, %IDC_HScroll, %SW_SHOW
si.cbSize = LEN(si)
si.fMask = %SIF_ALL
si.nPage = (1 - 1/zoom)*yp/4
si.nMax = 5 * si.nPage
si.nPos = 0 'ky * si.nPage
SetScrollInfo hVScroll, %SB_CTL, si, 1
ssi.cbSize = LEN(ssi)
ssi.fMask = %SIF_ALL
ssi.nPage = (1 - 1/zoom)*xp/4
ssi.nMax = 5 * ssi.nPage
ssi.nPos = 0 'kx * ssi.nPage
SetScrollInfo hHScroll, %SB_CTL, ssi, 1
x = ssi.nPos: y = 4 * si.nPage 'y = si.nPos
ELSE
x = 0: y = 0
CONTROL SHOW STATE CBHNDL, %IDC_VScroll, %SW_HIDE
CONTROL SHOW STATE CBHNDL, %IDC_HScroll, %SW_HIDE
END IF
InvalidateRect CBHNDL, r, 0
ELSEIF CBCTL = %IDC_Print THEN
printFile
ELSE
EXIT FUNCTION
END IF
IF zoom > 1 AND CBCTL < %IDC_Zoom THEN
zoom = 2.25: DIALOG SEND CBHNDL, %WM_COMMAND, %IDC_Zoom, 0
END IF
IF CBCTL < %IDC_Print THEN 'clear visible focus of buttons pressed
CONTROL SEND CBHNDL, CBCTL, %BM_SETSTYLE, %BS_PUSHBUTTON, %TRUE
END IF
CASE %WM_VSCROLL
SELECT CASE LOWRD(CBWPARAM)
CASE %SB_LINEDOWN, %SB_PAGEDOWN
si.nPos = MAX(si.nPos + si.nPage, si.nMin): y = y - si.nPage
CASE %SB_LINEUP, %SB_PAGEUP
si.nPos = MIN(si.nPos - si.nPage, si.nMax - si.nPage): y = y + si.nPage
CASE %SB_THUMBTRACK
si.nPos = MIN(HIWRD(CBWPARAM), si.nMax - si.nPage): y = 4 * si.nPage - si.nPos
CASE ELSE
EXIT FUNCTION
END SELECT
InvalidateRect CBHNDL, r, 0
si.cbSize = SIZEOF(si)
si.fMask = %SIF_POS OR %SIF_PAGE
SetScrollInfo hVScroll, %SB_CTL, si, 1
CASE %WM_HSCROLL
SELECT CASE LOWRD(CBWPARAM)
CASE %SB_LINEDOWN, %SB_PAGEDOWN
ssi.nPos = MIN(ssi.nPos + ssi.nPage, ssi.nMax - ssi.nPage): x = x + ssi.nPage
CASE %SB_LINEUP, %SB_PAGEUP
ssi.nPos = MAX(ssi.nPos - ssi.nPage, ssi.nMin): x = x - ssi.nPage
CASE %SB_THUMBTRACK
ssi.nPos = MIN(HIWRD(CBWPARAM), ssi.nMax - ssi.nPage): x = ssi.nPos
CASE ELSE
EXIT FUNCTION
END SELECT
InvalidateRect CBHNDL, r, 0
ssi.cbSize = SIZEOF(ssi)
ssi.fMask = %SIF_POS OR %SIF_PAGE
SetScrollInfo hHScroll, %SB_CTL, ssi, 1
CASE %WM_DESTROY
DeleteDC memdc
DeleteObject hBmp
XPRINT CANCEL
END SELECT
EXIT FUNCTION
previewPage:
IF nPage THEN
PatBlt memdc, 0, 0, xp, yp, %PATCOPY
printRTF memdc, 0, pageEnd(nPage-1) + 1, pageEnd(nPage)
GetDIBits(memDC, hBmp, 0, yp, BYVAL bitsPtr, BYVAL VARPTR(bmInfo), %DIB_RGB_COLORS)
InvalidateRect CBHNDL, r, 0: lastPage = nPage
CONTROL SET TEXT CBHNDL, %IDC_PageNo, STR$(MIN(nPage, numPages))
END IF
RETURN
END FUNCTION
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