Someone guide me here..

Alright, Here's the deal. I'm a C programmer. I've been programming C for two years now, and I have decided to jump into Windows Programming. I bought the book "Windows Programming" by Charles Petzold. It seems pretty straight forward but I've hit a bump, a very hard one. I'm stuck on chapter 4 - SYSMETS3.C.. It bascially teaches how to use and implement Scroll Bars in your app' but, I'm having a hard time understanding some of the stuff in the example - It's very frustrating. :mad:

What I want to know is: Would it be ok to skip Scroll Bars for the time being and move on? .. and later on when I'm through with the book, I can go back to Scroll bars? I really don't have much use for scroll bars ATM (but would definetl like to learn to use them) and the latter chapters only have 2/3 more examples with some scroll bar implementation in them so IMO, I think skipping Scroll bars would'nt really hamper my GUI progress. What do you think? should skip or not?

Thanks for reading this ;)

Yes, skip ahead if you want.

What is the problem you are having with scroll bars though?

Yes, it's entirely okay if you skip it. I did when I first read that book. In fact, I skipped alot of chapters in that book initially.

I only read those sections properly when I had to use topics discussed in them many months later.

Sorry, I meant to reply sooner but something came up so I could'nt.

I understand most of the code in the books scroll bars example now (thank goodness) but there's a few things still that I don't quite get how they work so here it ish:

Code:

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iPaintBeg = max(0, iVertPos + ps.rcPaint.top / cyChar);
iPaintEnd = min(NUMLINES - 1, iVertPos + ps.rcPaint.bottom / cyChar);

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This little peice of code was taken from charles petzolds chapter 4 - SYSMETS3.C example. If you could explain to me why I need to calculate ps.rcPaint.top and divide it by cyChar to find the painting limit and aslo for the one below it. I know that's meant to find the painting limits, but I don't get how it works. It's probably obvious to you guys but I don't see it.
Even though I seem to understand how to setp and use scroll bars, I still find it quite intimidating... it's a little hard to remember all this scroll bar stuff when there's so many parts to remember to get one simple app with scroll bars working. Know what I mean?

Here' the rest of the code:

Code:

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LRESULT CALLBACK WndProc(HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
        HDC                                hdc;
        PAINTSTRUCT                ps;
        RECT                        rect;
        TEXTMETRIC                tm;
        SCROLLINFO                si;
        static int cxChar, cyChar, cxCaps;
        static int cyClient, cxClient, iMaxWidth;
        int i, x, y, iVertPos, iHorzPos, iPaintBeg, iPaintEnd;
        char szBuffer[10];

        switch ( iMsg )
        {

        case WM_CREATE :
                hdc = GetDC(hwnd);

                GetTextMetrics(hdc, &tm);

                cxChar = tm.tmAveCharWidth;
                cxCaps = (tm.tmPitchAndFamily & 1 ? 3 : 2) * cxChar / 2;
                cyChar = tm.tmHeight + tm.tmExternalLeading;

                ReleaseDC(hwnd, hdc);

                // Save the width of the three colums
                iMaxWidth = 22 * cxCaps + 40 * cxChar; // In Pixels
                return 0;

        case WM_SIZE :
                cyClient = HIWORD(lParam);
                cxClient = LOWORD(lParam);

                // Set vertical scroll bar range and page size
                si.cbSize        = sizeof(si);
                si.fMask        = SIF_RANGE | SIF_PAGE;
                si.nMin                = 0;
                si.nMax                = NUMLINES - 1;
                si.nPage        = cyClient / cyChar;
                SetScrollInfo(hwnd, SB_VERT, &si, TRUE);

                // Set Horizontal scroll bar range and page size
                si.cbSize        = sizeof(si);
                si.fMask        = SIF_RANGE | SIF_PAGE;
                si.nMin                = 0;
                si.nMax                = 2 + iMaxWidth / cxChar;
                si.nPage        = cxClient / cxChar;
                SetScrollInfo(hwnd, SB_HORZ, &si, TRUE);
                return 0;

        case WM_VSCROLL :
                // Get all the vertical scroll bar information

                si.cbSize        = sizeof(si);
                si.fMask        = SIF_ALL;
                GetScrollInfo(hwnd, SB_VERT, &si);

                // Save the position for comparison later
                iVertPos = si.nPos;

                switch ( LOWORD(wParam) )
                {

                case SB_TOP :
                        si.nPos = si.nMin;
                        break;

                case SB_BOTTOM :
                        si.nPos = si.nMax;
                        break;

                case SB_LINEUP :
                        si.nPos -= 1;
                        break;

                case SB_LINEDOWN :
                        si.nPos += 1;
                        break;

                case SB_PAGEUP :
                        si.nPos -= si.nPage;
                        break;

                case SB_PAGEDOWN :
                        si.nPos += si.nPage;
                        break;

                case SB_THUMBTRACK :
                        si.nPos = si.nTrackPos;
                        break;

                default :
                        break;
                }

                // Set the position and then retrieve it
                si.fMask = SIF_POS;
                SetScrollInfo(hwnd, SB_VERT, &si, TRUE);
                GetScrollInfo(hwnd, SB_VERT, &si);

                // If the position has changed, scroll the widow and update it

                if ( si.nPos != iVertPos )
                {
                        ScrollWindow(hwnd, 0, cyChar * (iVertPos - si.nPos),
                                NULL, NULL);

                        UpdateWindow(hwnd);
                }
                return 0;

        case WM_HSCROLL :
                // Get all the horizontal bar information

                si.cbSize = sizeof(si);
                si.fMask = SIF_ALL;
                GetScrollInfo(hwnd, SB_HORZ, &si);

                // Save the position for comparinson later
                iHorzPos = si.nPos;

                switch ( LOWORD(wParam) )
                {
                       
                case SB_LINELEFT :
                        si.nPos -= 1;
                        break;

                case SB_LINERIGHT :
                        si.nPos += 1;
                        break;

                case SB_PAGELEFT :
                        si.nPos -= si.nPage;
                        break;
                       
                case SB_PAGERIGHT :
                        si.nPos += si.nPage;
                        break;

                case SB_THUMBPOSITION :
                        si.nPos = si.nTrackPos;
                        break;

                default :
                        break;
                }

                // Set the position and then retrieve it
                si.fMask = SIF_POS;
                SetScrollInfo(hwnd, SB_HORZ, &si, TRUE);
                GetScrollInfo(hwnd, SB_HORZ, &si);

                // If the position has changed, Scroll the window

                if ( si.nPos != iHorzPos )
                {
                        ScrollWindow(hwnd, cxChar * (iHorzPos - si.nPos),
                                0, NULL, NULL);
                }
                return 0;

        case WM_PAINT :
                hdc = BeginPaint(hwnd, &ps);

                // Get vertical scroll bar position
                si.fMask = SIF_POS;
                GetScrollInfo(hwnd, SB_VERT, &si);
                iVertPos = si.nPos;

                // Get Horizontal scroll bar position
                si.fMask = SIF_POS;
                GetScrollInfo(hwnd, SB_HORZ, &si);
                iHorzPos = si.nPos;

                //-- Can't seem to get how this code below works
                // Find painting limits
                iPaintBeg = max(0, iVertPos + ps.rcPaint.top / cyChar);
                iPaintEnd = min(NUMLINES - 1,
                        iVertPos + ps.rcPaint.bottom / cyChar);

                for ( i = iPaintBeg; i <= iPaintEnd; ++i )
                {
                        x = cxChar * (1 - iHorzPos);
                        y = cyChar * (i - iVertPos);

                        TextOut(hdc, x, y,
                                sysMetrics[i].szLabel,
                                strlen(sysMetrics[i].szLabel));

                        TextOut(hdc, x + 22 * cxCaps, y,
                                sysMetrics[i].szDescr,
                                strlen(sysMetrics[i].szDescr));

                        SetTextAlign(hdc, TA_TOP | TA_RIGHT);

                        TextOut(hdc, x + 22 * cxCaps + 40 * cxChar, y, szBuffer,
                                sprintf(szBuffer, "%d", GetSystemMetrics(sysMetrics[i].iIndex)));

                        SetTextAlign(hdc, TA_TOP | TA_LEFT);
                }

               
                EndPaint(hwnd, &ps);

                return 0;

        case WM_DESTROY :
                PostQuitMessage(0);
                return 0;

        default :
                break;
                }

                return DefWindowProc(hwnd, iMsg, wParam, lParam);
}

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Thanks in advanced.
xeddiex.