鼠标消息

对于所有的鼠标消息，其lParam值均含有鼠标位置：低字组为x坐标，高字组为y坐标，这两个坐标是相对于窗口显示区域左上角的位置。可以用LOWORD和HIWORD宏来提取这些值：

x = LOWORD(lParam);

y = HIWORD(lParam);

wParam值指示鼠标按键以及Shift和Ctrl键的状态。可以用WINUSER.H中定义的位屏蔽来测试wParam。例如：

收到了WM_LBUTTONDOWN的消息，而且值 wParam &ＭＫ＿ＳＨＩＦＴ是TRUE，就知道当左键按下时也按下了Ｓｈｉｆｔ键。

#include <windows.h>
#define MAXPOINTS 1000
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
	static TCHAR szAppName[] = TEXT("Connect");
	HWND hwnd;
	MSG msg;
	WNDCLASS wndclass;
	
	wndclass.style = CS_HREDRAW | CS_VREDRAW;
	wndclass.lpfnWndProc = WndProc;
	wndclass.cbClsExtra = 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("Context-the-Points Mouse Demo"),
		WS_OVERLAPPEDWINDOW, 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 POINT pt[MAXPOINTS];
	static int iCount;
	HDC hdc;
	int i, j;
	PAINTSTRUCT ps;
	switch (message)
	{
	case WM_LBUTTONDOWN:
		iCount = 0;
		InvalidateRect(hwnd, NULL, TRUE);
		return 0;
	case WM_MOUSEMOVE:
		if (wParam & MK_LBUTTON && iCount < MAXPOINTS)
		{
			pt[iCount].x = LOWORD(lParam);
			pt[iCount++].y = HIWORD(lParam);
			hdc = GetDC(hwnd);
			SetPixel(hdc, LOWORD(lParam), HIWORD(lParam), 0);
			ReleaseDC(hwnd, hdc);
		}
		return 0;

	case WM_LBUTTONUP:
		InvalidateRect(hwnd, NULL, FALSE);
		return 0;

	case WM_PAINT:
		hdc = BeginPaint(hwnd, &ps);
		SetCursor(LoadCursor(NULL, IDC_WAIT));
		ShowCursor(TRUE);
		for (i = 0; i < iCount - 1; ++i)
		{
			for (j = i + 1; j < iCount; ++j)
			{
				MoveToEx(hdc, pt[i].x, pt[i].y, NULL);
				LineTo(hdc, pt[j].x, pt[j].y);
			}
		}
		ShowCursor(FALSE);
		SetCursor(LoadCursor(NULL, IDC_ARROW));
		EndPaint(hwnd, &ps);
		return 0;

	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	}
	return DefWindowProc(hwnd, message, wParam, lParam);
}