正確使用 SetCapture ReleaseCapture [譯]「建议收藏」

#include <windows.h>

HINSTANCE g_hInstance = (HINSTANCE)GetModuleHandle(NULL);
HWND g_hMainWnd = NULL;
bool g_MovingMainWnd = false;
POINT g_OrigCursorPos;
POINT g_OrigWndPos;
LRESULT CALLBACK MainWndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
	switch (uMsg)
	{
	case WM_LBUTTONDOWN:
		// here you can add extra check and decide whether to start
		// the window move or not
		if (GetCursorPos(&g_OrigCursorPos))
		{
			RECT rt;
			GetWindowRect(hWnd, &rt);
			g_OrigWndPos.x = rt.left;
			g_OrigWndPos.y = rt.top;
			g_MovingMainWnd = true;
			SetCapture(hWnd);
		}
		return 0;
	// THE RIGHT WAY OF DOING IT:
	//*
	case WM_LBUTTONUP:
		ReleaseCapture();
		return 0;
	case WM_CAPTURECHANGED:
		g_MovingMainWnd = (HWND)lParam == hWnd;
		return 0;
	/**/
	// THE WRONG WAY OF DOING IT:
	/*
	case WM_LBUTTONUP:
		g_MovingMainWnd = false;
		ReleaseCapture();
		return 0;
	// buggy programs usually do not handle WM_CAPTURECHANGED at all
	case WM_CAPTURECHANGED:
		break;
	/**/
	case WM_MOUSEMOVE:
		if (g_MovingMainWnd)
		{
			POINT pt;
			if (GetCursorPos(&pt))
			{
				int wnd_x = g_OrigWndPos.x +
				  (pt.x - g_OrigCursorPos.x);
				int wnd_y = g_OrigWndPos.y +
				  (pt.y - g_OrigCursorPos.y);
				SetWindowPos(hWnd, NULL, wnd_x,
				  wnd_y, 0, 0, SWP_NOACTIVATE|
				  SWP_NOOWNERZORDER|SWP_NOZORDER|
				  SWP_NOSIZE);
			}
		}
		return 0;
	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	}
	return DefWindowProc(hWnd, uMsg, wParam, lParam);
}
bool CreateMainWnd()
{
	static const char CLASS_NAME[] = "MainWndClass";
	WNDCLASS wc;
	wc.cbClsExtra = 0;
	wc.cbWndExtra = 0;
	wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
	wc.hCursor = LoadCursor(NULL, IDC_ARROW);
	wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
	wc.hInstance = g_hInstance;
	wc.lpfnWndProc = &MainWndProc;
	wc.lpszClassName = CLASS_NAME;
	wc.lpszMenuName = NULL;
	wc.style = CS_HREDRAW | CS_VREDRAW | CS_DBLCLKS;
	if (!RegisterClass(&wc))
		return false;
	g_hMainWnd = CreateWindowEx(
		0,
		CLASS_NAME,
		"Main Window",
		WS_OVERLAPPED | WS_SYSMENU | WS_MINIMIZEBOX | WS_MAXIMIZEBOX,
		CW_USEDEFAULT, CW_USEDEFAULT, 300, 200,
		NULL,
		NULL,
		g_hInstance,
		NULL
		);
	return true;
}
int main()
{
	if (!CreateMainWnd())
		return -1;
	ShowWindow(g_hMainWnd, SW_SHOW);
	UpdateWindow(g_hMainWnd);
	MSG msg;
	while (GetMessage(&msg, NULL, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}
	return (int)msg.wParam;