判断鼠标是否点击矩形怎么实现

判断鼠标是否点击矩形，点击到矩形就变色，要怎么改？help

#include <windows.h>        

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
BOOL PtInRect(
    _In_ const RECT* lprc,  //矩形区域
    _In_       POINT pt   //当前点
);
int WINAPI WinMain(
    HINSTANCE hInstance,
    HINSTANCE hPrevInstance,
    PSTR szCmdLine,
    int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("HelloWin");
    HWND   hwnd;
    MSG    msg;
    WNDCLASS wndclass;
    wndclass.style = 0;
    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 = TEXT("MyClass");
    if (!RegisterClass(&wndclass))//(注册窗口类的API是RegisterClass)
    {
        MessageBox(NULL, TEXT("RegisterClass fail!"), szAppName, MB_ICONERROR);
        return 0;
    }
    //窗口起始位置(100,100)，大小300*400   
    hwnd = CreateWindow(
        TEXT("MyClass"),        // window class name
        szAppName,        // window caption
        WS_OVERLAPPEDWINDOW,    // window style
        100,            // initial x position
        100,            // initial y position
        630,            // initial x size
        520,            // initial y size
        NULL,                // parent window handle
        NULL,                // window menu handle
        hInstance,        // program instance handle
        NULL);            // creation parameters
    if (!hwnd)
    {
        MessageBox(NULL, TEXT("CreateWindow fail!!"), szAppName, MB_ICONERROR);
        return 0;
    }
    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)
{
    HDC hdc;
    PAINTSTRUCT ps;
    HPEN hOldPen, hPen1;
    static HBRUSH hBrush, hBrushR;
    switch (message)
    {
    case WM_CREATE:
        hBrush = (HBRUSH)GetStockObject(BLACK_BRUSH);
        hBrushR = CreateSolidBrush(RGB(255, 0, 0));
        return 0;



case WM_LBUTTONDOWN:
    {

        pt.x = LOWORD(lParam);   //当前鼠标位置
        pt.y = HIWORD(lParam);   //当前鼠标位置
        if (PtInRect(&hdc, pt)) {   //点击检测函数
            hBrush = hBrushR;
            break;
        }
 
    }break;


    case WM_LBUTTONUP: // 鼠标左键，抬起时刷新
        InvalidateRect(hwnd, NULL, FALSE);
        return 0;

    case WM_PAINT:

        hdc = BeginPaint(hwnd, &ps);
        hPen1 = CreatePen(HS_CROSS, 5, RGB(0, 0, 225));

        SelectObject(hdc, hBrush);

        //将hPen1选入设备环境
        hOldPen = (HPEN)SelectObject(hdc, hPen1);

        Rectangle(hdc, 50, 50, 150, 150);


        //删除创建的画刷
        DeleteObject(hBrush);

        //删除创建的画笔
        DeleteObject(hPen1);


        //释放设备环境
        EndPaint(hwnd, &ps);
        return 0;

        //恢复设备环境，将默认画笔选回
        SelectObject(hdc, hOldPen);

    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;

    case WM_KEYDOWN:
        hdc = GetDC(hwnd);
        ReleaseDC(hwnd, hdc);
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}

代码稍微修改了下，可以编译运行了，看注释

#include <windows.h>        

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
BOOL PtInRect(
    _In_ const RECT* lprc,  //矩形区域
    _In_       POINT pt   //当前点
);
int WINAPI WinMain(
    HINSTANCE hInstance,
    HINSTANCE hPrevInstance,
    PSTR szCmdLine,
    int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("HelloWin");
    HWND   hwnd;
    MSG    msg;
    WNDCLASS wndclass;
    wndclass.style = 0;
    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 = TEXT("MyClass");
    if (!RegisterClass(&wndclass))//(注册窗口类的API是RegisterClass)
    {
        MessageBox(NULL, TEXT("RegisterClass fail!"), szAppName, MB_ICONERROR);
        return 0;
    }
    //窗口起始位置(100,100)，大小300*400   
    hwnd = CreateWindow(
        TEXT("MyClass"),        // window class name
        szAppName,        // window caption
        WS_OVERLAPPEDWINDOW,    // window style
        100,            // initial x position
        100,            // initial y position
        630,            // initial x size
        520,            // initial y size
        NULL,                // parent window handle
        NULL,                // window menu handle
        hInstance,        // program instance handle
        NULL);            // creation parameters
    if (!hwnd)
    {
        MessageBox(NULL, TEXT("CreateWindow fail!!"), szAppName, MB_ICONERROR);
        return 0;
    }
    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)
{
    HDC hdc;
    PAINTSTRUCT ps;
    HPEN hOldPen, hPen1;
    static HBRUSH hBrush, hBrushR;
    switch (message)
    {
    case WM_CREATE:
        hBrush = (HBRUSH)GetStockObject(BLACK_BRUSH);
        hBrushR = CreateSolidBrush(RGB(255, 0, 0));
        return 0;



    case WM_LBUTTONDOWN:
    {
        //声明当前点变量
        POINT pt;
        //声明矩形框变量
        RECT rc;
        //矩形框变量赋值
        rc.left = 50;
        rc.top = 50;
        rc.right = 150;
        rc.bottom = 150;
        pt.x = LOWORD(lParam);   //当前鼠标位置
        pt.y = HIWORD(lParam);   //当前鼠标位置
        if (PtInRect(&rc, pt)) {   //点击检测函数
            hBrush = hBrushR;
            break;
        }

    }break;


    case WM_LBUTTONUP: // 鼠标左键，抬起时刷新
        InvalidateRect(hwnd, NULL, FALSE);
        return 0;

    case WM_PAINT:

        hdc = BeginPaint(hwnd, &ps);
        hPen1 = CreatePen(HS_CROSS, 5, RGB(0, 0, 225));

        SelectObject(hdc, hBrush);

        //将hPen1选入设备环境
        hOldPen = (HPEN)SelectObject(hdc, hPen1);

        Rectangle(hdc, 50, 50, 150, 150);


        //删除创建的画刷
        DeleteObject(hBrush);

        //删除创建的画笔
        DeleteObject(hPen1);


        //释放设备环境
        EndPaint(hwnd, &ps);
        return 0;

        //恢复设备环境，将默认画笔选回
        SelectObject(hdc, hOldPen);

    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;

    case WM_KEYDOWN:
        hdc = GetDC(hwnd);
        ReleaseDC(hwnd, hdc);
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}