六、Windows编程之鼠标滑轮
与传统的鼠标相比，Microsoft IntelliMouse的特点是在两个键之间多了一个小滑轮。您可以按下这个滑轮，这时它的功能相当于鼠标按键的中键；或者您也可以用食指来转动它，这会产生一条特殊的消息，叫做WM_MOUSEWHEEL。使用鼠标滑轮的程序通过滚动或放大文件来响应此消息。它最初听起来像一个不必要的隐藏机关，但我必须承认，我很快就习惯于使用鼠标滑轮来滚动Microsoft Word和Microsoft Internet Explorer了。
我不想讨论鼠标滑轮的所有使用方法。实际上，我只是想告诉您如何在现有的程序（例如程序SYSMETS4）中添加鼠标滑轮处理程序，以便在显示区域中卷动数据。最终的SYSMETS程序如程序7-8所示。
程序7-8 SYSMETS4
SYSMETS.C
/*----------------------------------------------------------------------------
SYSMETS.C -- Final System Metrics Display Program
(c) Charles Petzold, 1998
----------------------------------------------------------------------------*/
#include <windows.h>
#include "sysmets.h"
LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;
int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
static TCHAR szAppName[] = TEXT ("SysMets") ;
HWND hwnd ;
MSG msg ;
WNDCLASS wndclass ;
wndclass.style = CS_HREDRAW | CS_VREDRAW ;
wndclass.lpfnWndProc = WndProc ;
wndclass.cbClsExtra = 0 ;
wndclass.cbWndExtra = 0 ;
wndclass.hInstance = hInstance ;
wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ;
wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ;
wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
wndclass.lpszMenuName = NULL ;
wndclass.lpszClassName = szAppName ;
if (!RegisterClass (&wndclass))
{
MessageBox ( NULL, TEXT ("Program requires Windows NT!"),
szAppName, MB_ICONERROR) ;
return 0 ;
}
hwnd = CreateWindow (szAppName, TEXT ("Get System Metrics"),
WS_OVERLAPPEDWINDOW | WS_VSCROLL | WS_HSCROLL,
CW_USEDEFAULT, CW_USEDEFAULT,
CW_USEDEFAULT, CW_USEDEFAULT,
NULL, NULL, hInstance, NULL) ;
ShowWindow (hwnd, iCmdShow) ;
UpdateWindow (hwnd) ;
while (GetMessage (&msg, NULL, 0, 0))
{
TranslateMessage (&msg) ;
DispatchMessage (&msg) ;
}
return msg.wParam ;
}
LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam,LPARAM lParam)
{
static int cxChar, cxCaps, cyChar, cxClient, cyClient, iMaxWidth ;
static int iDeltaPerLine, iAccumDelta ; // for mouse wheel logic
HDC hdc ;
int i, x, y, iVertPos, iHorzPos, iPaintBeg, iPaintEnd ;
PAINTSTRUCT ps ;
SCROLLINFO si ;
TCHAR szBuffer[10] ;
TEXTMETRIC tm ;
ULONG ulScrollLines ; // for mouse wheel logic
switch (message)
{
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 columns
iMaxWidth = 40 * cxChar + 22 * cxCaps ;
// Fall through for mouse wheel information
case WM_SETTINGCHANGE:
SystemParametersInfo (SPI_GETWHEELSCROLLLINES, 0, &ulScrollLines, 0) ;
// ulScrollLines usually equals 3 or 0 (for no scrolling)
// WHEEL_DELTA equals 120, so iDeltaPerLine will be 40
if (ulScrollLines)
iDeltaPerLine = WHEEL_DELTA / ulScrollLines ;
else
iDeltaPerLine = 0 ;
return 0 ;
case WM_SIZE:
cxClient = LOWORD (lParam) ;
cyClient = HIWORD (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 on
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. Due to adjustments
// by Windows it may not be the same as the value set.
si.fMask = SIF_POS ;
SetScrollInfo (hwnd, SB_VERT, &si, TRUE) ;
GetScrollInfo (hwnd, SB_VERT, &si) ;
// If the position has changed, scroll the window 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 vertical scroll bar information
si.cbSize = sizeof (si) ;
si.fMask = SIF_ALL ;
// Save the position for comparison later on
GetScrollInfo (hwnd, SB_HORZ, &si) ;
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. Due to adjustments
// by Windows it may not be the same as the value set.
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_KEYDOWN :
switch (wParam)
{
case VK_HOME :
SendMessage (hwnd, WM_VSCROLL, SB_TOP, 0) ;
break ;
case VK_END :
SendMessage (hwnd, WM_VSCROLL, SB_BOTTOM, 0) ;
break ;
case VK_PRIOR :
SendMessage (hwnd, WM_VSCROLL, SB_PAGEUP, 0) ;
break ;
case VK_NEXT :
SendMessage (hwnd, WM_VSCROLL, SB_PAGEDOWN, 0) ;
break ;
case VK_UP :
SendMessage (hwnd, WM_VSCROLL, SB_LINEUP, 0) ;
break ;
case VK_DOWN :
SendMessage (hwnd, WM_VSCROLL, SB_LINEDOWN, 0) ;
break ;
case VK_LEFT :
SendMessage (hwnd, WM_HSCROLL, SB_PAGEUP, 0) ;
break ;
case VK_RIGHT :
SendMessage (hwnd, WM_HSCROLL, SB_PAGEDOWN, 0) ;
break ;
}
return 0 ;
case WM_MOUSEWHEEL:
if (iDeltaPerLine == 0)
break ;
iAccumDelta += (short) HIWORD (wParam) ; // 120 or -120
while (iAccumDelta >= iDeltaPerLine)
{
SendMessage (hwnd, WM_VSCROLL, SB_LINEUP, 0) ;
iAccumDelta -= iDeltaPerLine ;
}
while (iAccumDelta <= -iDeltaPerLine)
{
SendMessage (hwnd, WM_VSCROLL, SB_LINEDOWN, 0) ;
iAccumDelta += iDeltaPerLine ;
}
return 0 ;
case WM_PAINT :
hdc = BeginPaint (hwnd, &ps) ;
// Get vertical scroll bar position
si.cbSize = sizeof (si) ;
si.fMask = SIF_POS ;
GetScrollInfo (hwnd, SB_VERT, &si) ;
iVertPos = si.nPos ;
// Get horizontal scroll bar position
GetScrollInfo (hwnd, SB_HORZ, &si) ;
iHorzPos = si.nPos ;
// 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,
lstrlen (sysmetrics[i].szLabel)) ;
TextOut ( hdc, x + 22 * cxCaps, y,
sysmetrics[i].szDesc,
lstrlen (sysmetrics[i].szDesc)) ;
SetTextAlign (hdc, TA_RIGHT | TA_TOP) ;
TextOut ( hdc, x + 22 * cxCaps + 40 * cxChar, y, szBuffer,
wsprintf (szBuffer, TEXT ("%5d"),
GetSystemMetrics (sysmetrics[i].iIndex))) ;
SetTextAlign (hdc, TA_LEFT | TA_TOP) ;
}
EndPaint (hwnd, &ps) ;
return 0 ;
case WM_DESTROY :
PostQuitMessage (0) ;
return 0 ;
}
return DefWindowProc (hwnd, message, wParam, lParam) ;
}
转动滑轮会导致Windows在有输入焦点的窗口（不是鼠标光标下面的窗口）产生WM_MOUSEWHEEL消息。与平常一样，lParam将获得鼠标的位置，当然坐标是相对于屏幕左上角的，而不是显示区域的。另外，wParam的低字组包含一系列的旗标，用于表示鼠标按键、Shift与Ctrl键的状态。
新的信息保存在wParam的高字组。其中有一个「delta」值，该值目前可以是120或-120，这取决于滑轮的向前转动（也就是说，向鼠标的前面，即带有按钮与电缆的一端）还是向后转动。值120或-120表示文件将分别向上或向下卷动三行。这里的构想是，以后版本的鼠标滑轮能有比现在的鼠标产生更精确的移动速度信息，并且用delta值，例如40和-40，来产生WM_MOUSEWHEEL消息。这些值能使文件只向上或向下卷动一行。
为使程序能在一般化环境执行，SYSMETS将在WM_CREATE和WM_SETTINGCHANGE消息处理时，以SPI_GETWHEELSCROLLLINES作为参数来呼叫SystemParametersInfo。此值说明WHEEL_DELTA的delta值将滚动多少行，WHEEL_DELTA在WINUSER.H中定义。WHEEL_DELTA等于120，并且，在内定情况下SystemParametersInfo传回3，因此与卷动一行相联系的delta值就是40。SYSMETS将此值保存在iDeltaPerLine。
在WM_MOUSEWHEEL消息处理期间，SYSMETS将delta值给静态变量iAccumDelta。然后，如果iAccumDelta大于或等于iDeltaPerLine（或者是小于或等于-iDeltaPerLin），SYSMETS用SB_LINEUP或SB_LINEDOWN值产生WM_VSCROLL消息。对于每一个WM_VSCROLL消息，iAccumDelta由iDeltaPerLine增加（或减少）。此代码允许delta值大于、小于或等于滚动一行所需要的delta值。
下面还有
还有一个引人注目的鼠标问题：建立自订鼠标光标。我将在第十章，与其它Windows资源一起讨论此问题。
