从png, winapi创建透明图像

create transparent image from png, winapi

本文关键字：透明 透明图 图像 创建 winapi png      更新时间：2023-10-16

我创建了一个简单的表单在winapi中进行测试:我在这里上传:http://pastebin.com/7dNjE1Tb

我想把一个简单的png文件到我的hwnd，例如这个图片:http://www.ledavi-network.com/includes/images/bg_shadow_png.png

我知道我应该使用这个:http://msdn.microsoft.com/en-us/library/windows/desktop/dd145141(v=vs.85).aspx但我是winapi的新手，我找不到任何例子如何使用这个transparent - blt函数。

谁能帮我创建一个非常简单的例子?

编辑:但是我想做什么呢?我想创建一个带有阴影的特殊背景按钮。如果有人知道更简单的方法，我会忘记使用TransparentBlt。还有别的办法吗?

这样就可以了。您需要确保为AlphaBlend链接了gdiplus和msimg32库(TransparentBlt假设图像中的单个 rgb颜色将被视为透明的)。也就是说，当使用transparent(完全不透明或完全透明)时，它只是1位透明度。

您将(大概)希望使用AlphaBlend来完成这项工作。

注意-我没有费心添加一个WM_ERASEBKGND到WndProc函数。因此，每次重新绘制图像时，它都会直接绘制在已经存在的图像的顶部(尝试调整窗口大小)。只要在erasebkg中执行FillRect，就可以了。

编辑:代码更新为使用带有NULL hbitmap的displayImage来做背景。

这里‘:

#define WIN32_LEAN_AND_MEAN
#define WINVER 0x0600       // needed for alphablend function..
#include <windows.h>
#include <gdiplus.h>
const char g_szClassName[] = "myWindowClass";

// BMP, GIF, JPEG, PNG, TIFF, Exif, WMF, and EMF
// requires GDIPlus
HBITMAP mLoadImg(WCHAR *szFilename)
{
   HBITMAP result=NULL;
   Gdiplus::Bitmap* bitmap = new Gdiplus::Bitmap(szFilename,false);
   bitmap->GetHBITMAP(NULL, &result);
   delete bitmap;
   return result;
}
//void CStaticImg::displayImage(HBITMAP mBmp, HWND mHwnd)
void displayImage(HBITMAP mBmp, HWND mHwnd)
{
    RECT myRect;
    BITMAP bm;
    HDC screenDC, memDC;
    HBITMAP oldBmp;
    BLENDFUNCTION bf;
    GetObject(mBmp, sizeof(bm), &bm);
    bf.BlendOp = AC_SRC_OVER;
    bf.BlendFlags = 0;
    bf.SourceConstantAlpha = 0xff;
    bf.AlphaFormat = AC_SRC_ALPHA;
    screenDC = GetDC(mHwnd);
    GetClientRect(mHwnd, &myRect);
    if (mBmp == NULL)
        FillRect(screenDC, &myRect, WHITE_BRUSH);
    else
    {
        memDC = CreateCompatibleDC(screenDC);
        oldBmp = (HBITMAP)SelectObject(memDC, mBmp);
        AlphaBlend (screenDC, 0, 0, myRect.right,myRect.bottom, memDC, 0, 0, bm.bmWidth,bm.bmHeight, bf);
        SelectObject(memDC, oldBmp);
        DeleteDC(memDC);
        ReleaseDC(mHwnd, screenDC);
    }
}

// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    static HBITMAP myImage;
    switch(msg)
    {
        case WM_CLOSE:
            DestroyWindow(hwnd);
        break;
        case WM_ERASEBKGND:
            displayImage(NULL, hwnd);
        break;
        case WM_CREATE:
            myImage = mLoadImg(L"bg_shadow_png.png");
        break;
        case WM_PAINT:
            //displayImage(HBITMAP mBmp, HWND mHwnd);
            displayImage(myImage, hwnd);
            ValidateRect(hwnd, NULL);
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
        break;
        default:
            return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;
    static Gdiplus::GdiplusStartupInput gdiplusStartupInput;
    static ULONG_PTR gdiplusToken;
    // so we can load all the image formats that windows supports natively - (I'm using a transparent PNG on the main dialog)
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    //Step 1: Registering the Window Class
    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = g_szClassName;
    wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);
    if(!RegisterClassEx(&wc))
    {
        MessageBox(NULL, "Window Registration Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }
    // Step 2: Creating the Window
    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        g_szClassName,
        "The title of my window",
        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);
    // Step 3: The Message Loop
    while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    Gdiplus::GdiplusShutdown(gdiplusToken);
    return Msg.wParam;
}
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