Scrollbars, part 2

Managing scrollbars is not hard in principle. The basic idea is not that difficult, but there are a lot of small details that need to be ironed out. If you don't get the details just right, your program will feel odd in a strange way that you often can't pinpoint, much like a subtle background hum that makes you feel uneasy without realizing it. Getting the details right is important to making your program feel crisp and clean.

Let's start with a basic program and gradually add scrollbar features to it. The basic program merely displays one hundred numbered lines. Add these variables to the scratch program:

HFONT g_hfList;         /* Font for list */
int g_cyLine;           /* Height of each line */
int g_cItems = 100;     /* Number of items */

and add these functions to the scratch program:

BOOL
OnCreate(HWND hwnd, LPCREATESTRUCT lpcs)
{
    /* Create the font we use for the list */
    LOGFONT lf;
    SystemParametersInfo(SPI_GETICONTITLELOGFONT, sizeof(lf), &lf, 0);
    g_hfList = CreateFontIndirect(&lf);
    if (!g_hfList) return 0;

    /* Compute the height for each line */
    HDC hdc = GetDC(hwnd);
    HFONT hfPrev = SelectFont(hdc, g_hfList);
    SelectFont(hdc, hfPrev);
    SIZE siz;
    GetTextExtentPoint(hdc, TEXT("0"), 1, &siz);
    g_cyLine = siz.cy;

    ReleaseDC(hwnd, hdc);

    return 1;
}

void
OnDestroy(HWND hwnd)
{
    DeleteObject(g_hfList);
    PostQuitMessage(0);
}

/* This is a separate function for now; you'll see why later */
void
PaintSimpleContent(HWND hwnd, PAINTSTRUCT *pps)
{
    HFONT hfPrev = SelectFont(pps->hdc, g_hfList);  /* Use the right font */
    for (int i = 0; i < g_cItems; i++) {            /* Print all the lines */
        char szLine[256];
        int cch = wsprintf(szLine, "This is line %d", i);
        TextOut(pps->hdc, 0, i * g_cyLine, szLine, cch);
    }

    SelectFont(pps->hdc, hfPrev);
}

void
PaintContent(HWND hwnd, PAINTSTRUCT *pps)
{
    PaintSimpleContent(hwnd, pps);
}

We now have a base program upon which to build.

I'm sorry this is taking so long to get off the ground. But things finally get interesting in part 4, honest.