Scroll image horizontally - mfc

Question

I want to scroll image using scroll bar but when i used scrollwindow() function in OnHScroll method,it only scroll button present in dialog box not image.
I have used bitblt and stretchblt function to enlarge image using device context.I think by using dc information we can scroll image but i donot know i to do it.
Code of OnHScroll function is given below:
void CImgVeiwer::OnHScroll(UINT nSBCode, UINT nPos, CScrollBar* pcrollBar)
{
// TODO: Add your message handler code here and/or call default
int minpos;
int maxpos;
GetScrollRange(SB_HORZ, &minpos, &maxpos);
maxpos = GetScrollLimit(SB_HORZ);
CurPos = GetScrollPos(SB_HORZ);
switch (nSBCode)
{
case SB_LEFT: // Scroll to far left.
CurPos = minpos;
break;
case SB_RIGHT: // Scroll to far right.
CurPos = maxpos;
break;
case SB_ENDSCROLL: // End scroll.
break;
case SB_LINELEFT: // Scroll left.
if (CurPos > minpos)
CurPos--;
break;
case SB_LINERIGHT: // Scroll right.
if (CurPos < maxpos)
CurPos++;
break;
case SB_PAGELEFT: // Scroll one page left.
{
// Get the page size.
SCROLLINFO info;
GetScrollInfo(SB_HORZ, &info, SIF_ALL);
if (CurPos > minpos)
CurPos = max(minpos, CurPos - (int) info.nPage);
}
break;
case SB_PAGERIGHT: // Scroll one page right.
{
// Get the page size.
SCROLLINFO info;
GetScrollInfo(SB_HORZ, &info, SIF_ALL);
if (CurPos < maxpos)
CurPos = min(maxpos, CurPos + (int) info.nPage);
}
break;
case SB_THUMBPOSITION: // Scroll to absolute position. nPos is the position
CurPos = nPos; // of the scroll box at the end of the drag operation.
break;
case SB_THUMBTRACK: // Drag scroll box to specified position. nPos is the
CurPos = nPos; // position that the scroll box has been dragged to.
break;
}
// Set the new position of the thumb (scroll box).
m_HsrollFlag = TRUE;
SetScrollPos(SB_HORZ,CurPos);
ScrollWindow(-CurPos,0,0,0);
Invalidate();
CDialogEx::OnHScroll(nSBCode, nPos, pScrollBar);
}
Thanks In Advance

Answer 1

Finally ,I got solution to scroll image horizontally.
In above given code,remove the statement
ScrollWindow(-CurPos,0,0,0);
and add following statement in OnPaint() method, m_nWidth and nHeight are width and height of image you want to scroll.
dc.StretchBlt(ZERO - CurPos,FIFTY ,m_nWidth +1000,
nHeight+ 1000,
&memDC,ZERO,ZERO,m_nWidth,
m_nHeight,SRCCOPY);

Answer 2

By calling Invalidate() you cause the entire dialog to be repainted. So the ScrollWindow call is wasted: you are overpainting it in the subsequent WM_PAINT. Normally you would use ScrollWindow to scroll the visible part of the image, and then in WM_PAINT you only need to paint the uncovered edge left behind by the image scroll.
You should provide an lpRect parameter to ScrollWindow, and maybe lpClipRect as well. This will specify the area you want scrolled and also prevent the scrolling of child windows like buttons if they are outside of the image.