WM_NCHITTEST返回命中测试结果不准确，调用默认窗口过程前是否需要调整lParam？

最近在调试WM_NCHITTEST的逻辑时遇到了一个头疼的问题：明明传入的光标坐标看起来是正确的，但手动发送WM_NCHITTEST消息返回的命中测试值总是有偏差。想请教各位，在把lParam传给默认窗口过程之前，是不是需要做什么特殊的坐标调整？

先给大家看一下我用来复现问题的代码：

#include <windows.h>
#include <cstdio>
#include <functional>

int main(int, char**) {
    WNDCLASSEX wc = { 0 };
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.lpszClassName = TEXT("MRE");
    wc.lpfnWndProc = [](HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) -> LRESULT {
        static LRESULT ht = HTNOWHERE;
        switch (msg) {
            case WM_DESTROY:
                PostQuitMessage(0);
                return (LRESULT)0;
            case WM_NCLBUTTONDOWN:
                if ((wParam == HTCLOSE) || (wParam == HTMINBUTTON)) {
                    std::printf("\nstart ht: %d\n", wParam);
                    SetCapture(hwnd);
                    ht = wParam;
                    return (LRESULT)0;
                }
                break;
            case WM_NCLBUTTONUP:
            case WM_LBUTTONUP:
                if (ht == HTNOWHERE) break;
                ReleaseCapture();
                ht = HTNOWHERE;
                RECT rect = { };
                GetWindowRect(hwnd, &rect);
                std::printf("window (%d x %d) at (%d, %d)\n", rect.right - rect.left, rect.bottom - rect.top, rect.left, rect.top );
                POINT p = { };
                bool bSuccess = GetCursorPos(&p);
                std::printf("%d at (%d, %d)\n", bSuccess, p.x, p.y);
                std::printf("end ht: %d\n", SendMessage(hwnd, WM_NCHITTEST, 0, MAKELPARAM(p.x, p.y)));
                break;
        }
        return DefWindowProc(hwnd, msg, wParam, lParam);
    };

    if (!RegisterClassEx(&wc)) return 1;

    const LONG styles = (WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_MINIMIZEBOX);
    RECT rectDimensions = { 0u, 0u, 640u, 480u };
    AdjustWindowRect(&rectDimensions, styles, false);
    HWND hwnd = CreateWindow(
        TEXT("MRE"), TEXT("mre"), styles,
        0, 0, (rectDimensions.right - rectDimensions.left), (rectDimensions.bottom - rectDimensions.top),
        nullptr, nullptr, GetModuleHandle(NULL), nullptr
    );

    MSG msg = { 0 };
    ShowWindow(hwnd, SW_NORMAL);
    while (GetMessage(&msg, nullptr, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return 0;
}

我运行这段代码后得到了以下测试结果：

注：start ht是默认窗口过程在WM_NCLBUTTONDOWN时返回的正确命中目标；end ht是我手动发送WM_NCHITTEST后得到的不准确结果；另外(2)对应HTCAPTION，(9)对应HTMAXBUTTON

测试场景1：左键按下最小化按钮（HTMINBUTTON=8），在屏幕左上角抬起左键 #

start ht: 8
window (656 x 519) at (1042, 297)
1 at (0, 0)
end ht: 0

测试场景2：抬起左键时期望命中HTMINBUTTON(8) #

理论上HTMINBUTTON应该在窗口原点右侧530px到576px的范围内，我测试的几次坐标都在这个区间里，但返回结果却不稳定：

start ht: 8
window (656 x 519) at (1042, 297)
1 at (1556, 315)
end ht: 2

start ht: 8
window (656 x 519) at (1042, 297)
1 at (1570, 308)
end ht: 2

start ht: 8
window (656 x 519) at (1042, 297)
1 at (1594, 312)
end ht: 8

测试场景3：抬起左键时期望命中HTCLOSE(20) #

同样出现了返回结果不符合预期的情况：

start ht: 20
window (656 x 519) at (1042, 297)
1 at (1646, 307)
end ht: 9

start ht: 20
window (656 x 519) at (1042, 297)
1 at (1664, 311)
end ht: 20

start ht: 20
window (656 x 519) at (1042, 297)
1 at (1683, 311)
end ht: 20

我确认了GetCursorPos()返回的屏幕坐标是正确的，而且我理解WM_NCHITTEST接收的就是屏幕坐标，所以直接用这个结果应该没问题。为了解决这个问题我已经尝试了几种方法，但都没有效果：

• 在程序开头调用SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2)开启Per-Monitor V2的DPI感知（因为用应用清单的方式不可行）
• 使用PhysicalToLogicalPointForPerMonitorDPI()转换光标坐标后再传入WM_NCHITTEST：

  POINT p = { };
  bool bResult = ((GetCursorPos(&p)) && (PhysicalToLogicalPointForPerMonitorDPI(hwnd, &p)));
  std::printf("%d at (%d, %d)\n", bResult, p.x, p.y);
  std::printf("end ht: %d\n", SendMessage(hwnd, WM_NCHITTEST, 0, MAKELPARAM(p.x, p.y)));
  

• 直接使用WM_NCLBUTTONUP消息的lParam作为坐标：
  修改了窗口过程中WM_NCLBUTTONUP的处理逻辑，直接从lParam提取坐标，结果和GetCursorPos()返回的完全一致，但问题依旧存在。

现在实在是搞不懂问题出在哪了，有没有大佬能帮忙分析下？是不是我对WM_NCHITTEST的坐标要求理解错了，或者确实需要对lParam做什么特殊的调整？

内容来源于stack exchange