具有透明背景的win32菜单项位图

Question

我尝试完成的工作非常简单：将图像添加到菜单项。我正在使用 win32 API 在 C 中编程。图像/位图显示，但背景是白色的。我想要的是把白色背景变成透明的。

我一直在阅读我能找到的所有信息，包括 stackoverflow，但信息似乎不一致。有人说位图不能具有任何形式的透明度，而另一些人则说它可以。例如看这个问题：

Simple way to show a bitmap next to a menu item in a CMenu with correct transparency

SetMenuItemBitmaps() 和 SetMenuItemInfo() 都提供白色背景。上面的链接说如果位图是 32bpp 的预乘 alpha，它应该正确显示。因此，要么根本不可能，要么我使用的 bmp 格式错误。任何人都可以对这个问题给出明确的答案。如果事实证明无法使用SetMenuItemInfo() 完成，那么解决此问题的最简单方法是什么？我尽量避免所有者绘制解决方案，因为我觉得这有点矫枉过正。此外，据我了解，所有者绘制的解决方案很难尊重 Windows 主题。

menubitmap.rc:

#include "menubitmap.h"

ID_ICON             ICON    DISCARDABLE "menu1.ico"
ID_BITMAP_EXIT      BITMAP  DISCARDABLE "Exit-icn.bmp"

ID_MENU MENU DISCARDABLE 
BEGIN
    POPUP "&File"
    BEGIN
        MENUITEM "E&xit",                       ID_FILE_EXIT
    END
END

menubitmap.c:

#include <windows.h>
#include "menubitmap.h"

const char g_szClassName[] = "myWindowClass";

LRESULT CALLBACK WndProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam)
{
    switch(Message)
    {
        case WM_CREATE:
        {
            HBITMAP btmp;
            MENUITEMINFOA miinfo;
            HMENU menu;

            btmp=LoadBitmap((HINSTANCE) GetModuleHandle (NULL), MAKEINTRESOURCE(ID_BITMAP_EXIT));
            menu=GetMenu(hwnd);
            miinfo.cbSize=sizeof(MENUITEMINFO);
            if(!GetMenuItemInfo(menu,ID_FILE_EXIT,FALSE,&miinfo)){
                    printf("getmenuiteminfo failed\r\n");
            }else{
                    miinfo.fMask |= MIIM_BITMAP;
                    miinfo.hbmpItem=btmp;
                    if(SetMenuItemInfo(menu,ID_FILE_EXIT,FALSE,&miinfo)){
                            printf("setmenuiteminfo");
                    }
            }

        }
        case WM_COMMAND:
            switch(LOWORD(wParam))
            {
                case ID_FILE_EXIT:
                    PostMessage(hwnd, WM_CLOSE, 0, 0);
                break;
            }
        break;
        case WM_CLOSE:
            DestroyWindow(hwnd);
        break;
        case WM_DESTROY:
            PostQuitMessage(0);
        break;
        default:
            return DefWindowProc(hwnd, Message, wParam, lParam);
    }
    return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;

    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(GetModuleHandle(NULL), MAKEINTRESOURCE(ID_ICON));
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
    wc.lpszMenuName  = MAKEINTRESOURCE(ID_MENU);
    wc.lpszClassName = g_szClassName;
    wc.hIconSm       = (HICON)LoadImage(GetModuleHandle(NULL), MAKEINTRESOURCE(ID_ICON), IMAGE_ICON, 16, 16, 0);

    if(!RegisterClassEx(&wc))
    {
        MessageBox(NULL, "Window Registration Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        g_szClassName,
        "A Menu",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 240, 120,
        NULL, NULL, hInstance, NULL);

    if(hwnd == NULL)
    {
        MessageBox(NULL, "Window Creation Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}

在这里你可以找到bitmap

这是 bas64 格式的位图：
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Answer 1

Windows 的 GDI 中的 Alpha 透明度是一个雷区。它添加得很晚，只有少数 API 调用真正能够处理专用的 Alpha 通道。 LoadBitmap 不是支持（或至少不破坏）alpha 透明度的那些之一。当您从应用程序的资源加载图像时，alpha 通道会丢失。

要解决这个问题，您必须使用LoadImage，并传入正确的标志。 LR_CREATEDIBSECTION 是重要的，因为它保留了源位图中的 Alpha 通道。

修复就像替换一样简单

LoadBitmap((HINSTANCE) GetModuleHandle (NULL), MAKEINTRESOURCE(ID_BITMAP_EXIT))

与

(HBITMAP)LoadImage(GetModuleHandle(NULL), MAKEINTRESOURCE(ID_BITMAP_EXIT),
                   IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION)

设置好之后，您将看到以每像素 Alpha 透明度显示的菜单图标：

Answer 2

您可以手动更改位图的背景颜色以实现透明度。

代码如下：

void swap_color(HBITMAP hbmp)
{
    if(!hbmp)
        return;
    HDC hdc = ::GetDC(HWND_DESKTOP);
    BITMAP bm;
    GetObject(hbmp, sizeof(bm), &bm);
    BITMAPINFO bi = { 0 };
    bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bi.bmiHeader.biWidth = bm.bmWidth;
    bi.bmiHeader.biHeight = bm.bmHeight;
    bi.bmiHeader.biPlanes = 1;
    bi.bmiHeader.biBitCount = 32;

    std::vector<uint32_t> pixels(bm.bmWidth * bm.bmHeight);
    GetDIBits(hdc, hbmp, 0, bm.bmHeight, &pixels[0], &bi, DIB_RGB_COLORS);

    //assume that the color at (0,0) is the background color
    uint32_t color_old = pixels[0];

    //this is the new background color
    uint32_t bk = GetSysColor(COLOR_MENU);

    //swap RGB with BGR
    uint32_t color_new = RGB(GetBValue(bk), GetGValue(bk), GetRValue(bk));

    for (auto &pixel : pixels)
        if(pixel == color_old)
            pixel = color_new;

    SetDIBits(hdc, hbmp, 0, bm.bmHeight, &pixels[0], &bi, DIB_RGB_COLORS);
    ::ReleaseDC(HWND_DESKTOP, hdc);
}

最少的代码示例：

HMENU m_hMenu;
HBITMAP g_BitMap;
...
case WM_CONTEXTMENU:
        {           
            m_hMenu = CreatePopupMenu();
            g_BitMap = (HBITMAP)LoadImage(NULL, L"UNTITLED.bmp", IMAGE_BITMAP, 16, 16, LR_LOADFROMFILE);
            swap_color(g_BitMap);
            InsertMenu(m_hMenu, 1, MF_BYPOSITION | MF_POPUP, NULL, L"Windows");
            MENUITEMINFO mii = { sizeof(MENUITEMINFO) };
            mii.fMask = MIIM_BITMAP;
            mii.hbmpItem = g_BitMap;
            SetMenuItemInfo(m_hMenu, 0, true, &mii);            
            TrackPopupMenu(m_hMenu, TPM_TOPALIGN | TPM_LEFTALIGN | TPM_HORPOSANIMATION, GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam), 0, hWnd, NULL);   
        }
        break;

调试：

您提到的link 中的img，我将其转换为32-bit BMP picture。

参考：How to show menu bitmaps with transparent background