绘制线WINAPI

Question

我想通过点击并将光标从一个点移动到另一个点来画一条线，我刚刚复制了下面的代码，我的WindowProcedure看起来是这样的：

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{   
    //PAINTSTRUCT ps;
    HDC hdc;
    bool draw = false;
    int x = 0, y=0;

    //InvalidateRect(hwnd, NULL, true);
    switch (uMsg)
    {
    case WM_LBUTTONDOWN:
            draw = true;
            x = LOWORD(lParam);
            y = HIWORD(lParam);
            return 0;

    case WM_LBUTTONUP:
        if (draw)
        {
            hdc = GetDC(hwnd);
            MoveToEx(hdc, x, y, NULL);
            LineTo(hdc, LOWORD(lParam), HIWORD(lParam));
            ReleaseDC(hwnd, hdc);
        }
        draw = FALSE;
        return 0;

    case WM_MOUSEMOVE:
        if (draw)
        {
            hdc = GetDC(hwnd);
            MoveToEx(hdc, x, y, NULL);
            LineTo(hdc, x = LOWORD(lParam), y = HIWORD(lParam));
            ReleaseDC(hwnd, hdc);
        }
        return 0;


    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;

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

但是当我点击的时候，什么都没有发生，就像一次只能处理一个案例，对吗？当我注释前两个案例时，它会画线，所以它会进入switch，但这不是我想要做的。有什么建议吗？

Answer 1

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{   
    //PAINTSTRUCT ps;
    HDC hdc;
    static bool draw = false;  // ←static
    static int x = 0, y=0;     // ←

这个怎么样？