[c++] gdiplus绘制透明异型窗口

本来是想使用 GDI+ 制作一个透明窗口，然后使用 SetWindowDisplayAffinity 来实现反截屏的目的，但是遗憾的是针对 WS_EX_LAYERED 属性的窗口，SetWindowDisplayAffinity 的调用总是会失败，返回错误码 ：8 。

但是写都写了，就记录下来备忘吧。
（代码参考自网络，结构上做了一些小修改，侵删）

#include <iostream>
#include <Windows.h>
#include <gdiplus.h>

#pragma comment(lib,"gdiplus.lib")

typedef BOOL(*UPDATELAYEREDWINDOWFUNCTION)(HWND, HDC, POINT*, SIZE*, HDC, POINT*, COLORREF, BLENDFUNCTION*, DWORD);

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_DESTROY:
        PostQuitMessage(0);       
        break;
    case WM_LBUTTONDOWN:
        break;
    default:
        return DefWindowProc(hwnd, message, wParam, lParam);
    }
    return 0;
}

int main()
{
    //
    // 变量定义
    //

    ULONG_PTR gdiplusStartupToken;
    Gdiplus::GdiplusStartupInput gdiInput;
    HWND hwnd;
    MSG messages;
    WNDCLASSEX wincl;
    HINSTANCE hThisInstance = GetModuleHandle(0);
    char szClassName[] = "PNGDialog";
    RECT wndRect;
    SIZE wndSize;
    HDC hdc;
    HDC memDC;
    HBITMAP memBitmap;
    HMODULE hUser32;
    UPDATELAYEREDWINDOWFUNCTION UpdateLayeredWindow;
    HDC screenDC;
    POINT ptSrc;
    BLENDFUNCTION blendFunction;

    //
    // 初始化 GDI+
    //

    Gdiplus::GdiplusStartup(&gdiplusStartupToken, &gdiInput, NULL);

    //
    // 定义窗口结构
    //

    wincl.hInstance = hThisInstance; 
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;
    wincl.style = CS_DBLCLKS;
    wincl.cbSize = sizeof(WNDCLASSEX);
    wincl.hIcon = NULL;
    wincl.hIconSm = NULL;
    wincl.hCursor = NULL;
    wincl.lpszMenuName = NULL;
    wincl.cbClsExtra = 0;
    wincl.cbWndExtra = 0;
    wincl.hbrBackground = (HBRUSH)COLOR_BACKGROUND;

    //
    // 注册窗口类
    //

    if (!RegisterClassEx(&wincl))
    {
        printf("RegisterClassEx error : %d \n", GetLastError());
        return 0;
    }

    //
    // 创建窗口
    //
    
    hwnd = CreateWindowEx(
        WS_EX_LAYERED | WS_EX_TOOLWINDOW | WS_EX_TOPMOST,
        szClassName,
        "PNGDialog Example Application",    
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,
        CW_USEDEFAULT, 
        500,                
        500,                 
        HWND_DESKTOP,       
        NULL,               
        hThisInstance,      
        NULL              
    );

    //
    // 使窗口在屏幕上可见
    //

    ShowWindow(hwnd, SW_SHOW);
    LONG style = ::GetWindowLong(hwnd, GWL_STYLE);
    if (style & WS_CAPTION)
        style ^= WS_CAPTION;
    if (style & WS_THICKFRAME)
        style ^= WS_THICKFRAME;
    if (style & WS_SYSMENU)
        style ^= WS_SYSMENU;
    ::SetWindowLong(hwnd, GWL_STYLE, style);
    style = ::GetWindowLong(hwnd, GWL_EXSTYLE);
    if (style & WS_EX_APPWINDOW)
        style ^= WS_EX_APPWINDOW;
    ::SetWindowLong(hwnd, GWL_EXSTYLE, style);

    //
    // 使用 GDI+ 加载图片
    //

    ::GetWindowRect(hwnd, &wndRect);
    wndSize = { wndRect.right - wndRect.left,wndRect.bottom - wndRect.top };
    hdc = ::GetDC(hwnd);
    memDC = ::CreateCompatibleDC(hdc);
    memBitmap = ::CreateCompatibleBitmap(hdc, wndSize.cx, wndSize.cy);
    ::SelectObject(memDC, memBitmap);
    Gdiplus::Image image(L"pic.png");
    Gdiplus::Graphics graphics(memDC);
    graphics.DrawImage(&image, 0, 0, wndSize.cx, wndSize.cy);

    //
    // 获取 UpdateLayeredWindow 函数地址
    //

    hUser32 = ::LoadLibrary("User32.dll");
    if (!hUser32)
    {
        return FALSE;
    }
    UpdateLayeredWindow = (UPDATELAYEREDWINDOWFUNCTION)::GetProcAddress(hUser32, "UpdateLayeredWindow");
    if (!UpdateLayeredWindow)
    {
        return FALSE;
    }

    //
    // 获取屏幕 DC
    //

    screenDC = GetDC(NULL);
    ptSrc = { 0,0 };

    //
    // 绘制窗口
    //

    blendFunction.AlphaFormat = AC_SRC_ALPHA;
    blendFunction.BlendFlags = 0;
    blendFunction.BlendOp = AC_SRC_OVER;
    blendFunction.SourceConstantAlpha = 255;
    UpdateLayeredWindow(hwnd, screenDC, &ptSrc, &wndSize, memDC, &ptSrc, 0, &blendFunction, 2);
    ::DeleteDC(memDC);
    ::DeleteObject(memBitmap);

  
    //
    // 反截屏（会失败，原因是只能对 WS_EX_TOPMOST 类型的窗口使用）
    //

    /*if (!SetWindowDisplayAffinity(hwnd, WDA_MONITOR))
    {
        printf("SetWindowDisplayAffinity error : %d \n", GetLastError());
    }*/

    //
    // 进入消息循环
    //

    while (GetMessage(&messages, NULL, 0, 0))
    {
        TranslateMessage(&messages);
        DispatchMessage(&messages);
    }
    Gdiplus::GdiplusShutdown(gdiplusStartupToken);


    (void)getchar();
    return 0;
}

效果图：