2.填充黑色 因为Alpha通道黑色+前景色黑色时会完全透明

3.用滤镜做如下效果

4.选择全部区域并复制 增加Alpha通道

5.通道中只选Alpha通道 并粘贴选择区域

6.存盘为BMP格式 这是Alpha通道自动选择

7.BMP选项为Windows 32位

8.效果图 边沿透明不规则

说明：UpdateLayeredWindow函数做透明处理时有两个参数可以调整透明度
一个是BMP中的Alpha通道的参数，还有一个是BLENDFUNCTION结构中的SourceConstantAlpha参数

pre { color: rgba(32, 48, 64, 1); background-color: rgba(235, 243, 252, 1); border: 1px dashed rgba(47, 111, 171, 1); font-family: 宋体; font-size: 9pt; line-height: 1.2em; overflow: auto; padding: 0.2em; white-space: pre }

void CUpdateLayeredWindow_testDlg::Test()
{
	char bmpFileName[] = {"./back.bmp"};
	HWND hWnd = this->GetSafeHwnd();
	typedef BOOL (WINAPI *pfnUpdateLayeredWindow)(HWND hWnd, HDC hdcDst, POINT *pptDst,
		SIZE *psize, HDC hdcSrc, POINT *pptSrc, COLORREF crKey,
		BLENDFUNCTION *pblend, DWORD dwFlags);
	pfnUpdateLayeredWindow s_UpdateLayeredWindow;
	HMODULE hSysDll = LoadLibrary(_T("USER32.DLL"));
	if(!hSysDll) return;
	s_UpdateLayeredWindow = 
		(pfnUpdateLayeredWindow)GetProcAddress(hSysDll, 
		"UpdateLayeredWindow");
	if(!s_UpdateLayeredWindow) return;
	HBITMAP hbitmap = (HBITMAP)::LoadImage(AfxGetInstanceHandle(),bmpFileName,
		IMAGE_BITMAP,0,0,LR_LOADFROMFILE);
	if(!hbitmap) return;
	DWORD dwExStyle = ::GetWindowLong(hWnd, GWL_EXSTYLE);
	if ((dwExStyle & 0x80000) != 0x80000)
		::SetWindowLong(hWnd, GWL_EXSTYLE, dwExStyle ^ 0x80000);
	HDC hMemDC = CreateCompatibleDC(NULL);
	HBITMAP hOriBmp = (HBITMAP)SelectObject(hMemDC, hbitmap);
	BITMAP bi;
	CBitmap bm;
	bm.Attach(hbitmap);
	bm.GetBitmap(&bi);
	bm.Detach();
	SetWindowPos(NULL,0,0,bi.bmWidth,bi.bmHeight,0);
	RECT WndRect;
	::GetWindowRect(hWnd, &WndRect);
	POINT ptDst = {WndRect.left, WndRect.top};
	POINT ptSrc = {0, 0};
	SIZE WndSize = {WndRect.right-WndRect.left,WndRect.bottom-WndRect.top};
	#define AC_SRC_ALPHA 0x01
	#define ULW_ALPHA 0x00000002
	BLENDFUNCTION blendPixelFunction= { AC_SRC_OVER, 0, 255, AC_SRC_ALPHA };
	BOOL bRet= s_UpdateLayeredWindow(m_hWnd, NULL, &ptDst, &WndSize, hMemDC,
		&ptSrc, 0, &blendPixelFunction, 2);
	SelectObject(hMemDC, hOriBmp);
	DeleteObject(hbitmap);
	DeleteDC(hMemDC);
}

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