duilib 使用图片素材或者算法给窗体增加阴影（源码和demo）

转载请说明原出处，谢谢：http://blog.csdn.net/zhuhongshu/article/details/42580877

之前我写的程序使用阴影时，一直是使用codeproject网站上的WndShadow类，并且把它当作单独的模块来使用，后来觉得使用阴影的情况非常多，所以今天就把这个类改写了一下，让他融入到duilib，并且可以直接使用xml来描述阴影，不需要写任何c++代码。

以前的WndShadow类是用算法来计算阴影，灵活性很大，但是缺点就是效果不够理想，所以我另外给他附加了使用图片素材来贴阴影的功能。最终的新类名为CShadowUI。这个类可以单独使用，我把他集成到了自己的库里。为了融合到Duilib我修改了UiLib.h文件、UIDlgBuilder.cpp文件、UIManager.h文件、UIManager.cpp文件。

先贴两张效果图，以下是素材阴影和算法阴影的效果图：

通过设置xml的Window标签可以添加阴影，阴影的xml属性描述如下：

		<Attribute name="showshadow" default="false" type="BOOL" comment="是否启用窗体阴影"/>
		<Attribute name="shadowimage" default="" type="STRING" comment="阴影图片，使用此属性后自动屏蔽算法阴影(不支持source等属性设置)"/>
		<Attribute name="shadowcorner" default="0,0,0,0" type="RECT" comment="图片阴影的九宫格描述"/>
		<Attribute name="shadowsize" default="0" type="BYTE" comment="算法阴影的宽度(-20到20)"/>
		<Attribute name="shadowsharpness" default="255" type="BYTE" comment="算法阴影的锐度"/>
		<Attribute name="shadowdarkness" default="255" type="BYTE" comment="算法阴影的深度(相当于透明度)"/>
		<Attribute name="shadowpositon" default="0,0" type="SIZE" comment="算法阴影的偏移量"/>
		<Attribute name="shadowcolor" default="0x000000" type="DWORD" comment="算法阴影的颜色，RGB格式，不支持透明度，使用shadowdarkness设置透明度"/>

前面的两个效果图的对应xml描述如下：

<!-- 图片阴影 -->
<Window size="840,600" sizebox="4,4,4,4" caption="0,0,0,75" mininfo="840,600" showshadow="true" shadowimage="shadow.png" shadowcorner="23,13,23,33">
<!-- 算法阴影 -->
<Window size="840,600" sizebox="4,4,4,4" caption="0,0,0,75" mininfo="840,600" showshadow="true" shadowsize="5" shadowpositon="1,1" shadowcolor="#333333">

源码：

       UIShadow.h源码为：

// WndShadow.h : header file
//
// Version 0.1
//
// Copyright (c) 2006 Perry Zhu, All Rights Reserved.
//
// mailto:perry@live.com
//
//
// This source file may be redistributed unmodified by any means PROVIDING
// it is NOT sold for profit without the authors expressed written
// consent, and providing that this notice and the author's name and all
// copyright notices remain intact. This software is by no means to be
// included as part of any third party components library, or as part any
// development solution that offers MFC extensions that are sold for profit.
//
// If the source code is used in any commercial applications then a statement
// along the lines of:
//
// "Portions Copyright (c) 2006 Perry Zhu" must be included in the "Startup
// Banner", "About Box" or "Printed Documentation". This software is provided
// "as is" without express or implied warranty. Use it at your own risk! The
// author accepts no liability for any damage/loss of business that this
// product may cause.
//
/////////////////////////////////////////////////////////////////////////////
//****************************************************************************

/********************************************************************
	created:	2015/01/09
	filename: 	UIShadow.h
	author:		Redrain

	purpose:	DuiLib阴影类，在原WndShadow类的基础上，增加了通过PNG图片设置阴影的功能，并且把代码与DuiLib融合
*********************************************************************/

#ifndef __UISHADOW_H__
#define __UISHADOW_H__

#pragma once
#include "map"

namespace DuiLib
{
typedef BOOL (WINAPI *pfnUpdateLayeredWindow)(HWND hWnd, HDC hdcDst, POINT *pptDst,
		SIZE *psize, HDC hdcSrc, POINT *pptSrc, COLORREF crKey,
		BLENDFUNCTION *pblend, DWORD dwFlags);

class UILIB_API CShadowUI
{
public:
	friend class CPaintManagerUI;

	CShadowUI(void);
	virtual ~CShadowUI(void);

public:
	// bShow为真时才会创建阴影
	void ShowShadow(bool bShow);
	bool IsShowShadow() const;

	// 算法阴影的函数
	bool SetSize(int NewSize = 0);
	bool SetSharpness(unsigned int NewSharpness = 5);
	bool SetDarkness(unsigned int NewDarkness = 200);
	bool SetPosition(int NewXOffset = 5, int NewYOffset = 5);
	bool SetColor(COLORREF NewColor = 0);

	// 图片阴影的函数
	bool SetImage(LPCTSTR szImage);
	bool SetShadowCorner(RECT rcCorner);	// 九宫格方式描述阴影

protected:

	//	初始化并注册阴影类
	static bool Initialize(HINSTANCE hInstance);

	//	创建阴影窗体，由CPaintManagerUI自动调用
	void Create(CPaintManagerUI* pPaintManager);

	//	子类化父窗体
	static LRESULT CALLBACK ParentProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

	// 父窗体改变大小，移动，或者主动重绘阴影时调用
	void Update(HWND hParent);

	// 通过算法计算阴影
	void MakeShadow(UINT32 *pShadBits, HWND hParent, RECT *rcParent);

	// 计算alpha预乘值
	inline DWORD PreMultiply(COLORREF cl, unsigned char nAlpha)
	{
		return (GetRValue(cl) * (DWORD)nAlpha / 255) |
			(GetGValue(cl) * (DWORD)nAlpha / 255) << 8 |
			(GetBValue(cl) * (DWORD)nAlpha / 255) << 16 ;
	}

protected:
	enum ShadowStatus
	{
		SS_ENABLED = 1,				// Shadow is enabled, if not, the following one is always false
		SS_VISABLE = 1 << 1,		// Shadow window is visible
		SS_PARENTVISIBLE = 1<< 2	// Parent window is visible, if not, the above one is always false
	};

	// 保存已经附加的窗体句柄和与其关联的阴影类,方便在ParentProc()函数中通过句柄得到阴影类
	static std::map<HWND, CShadowUI *> *s_Shadowmap;
	static bool s_bHasInit;

	CPaintManagerUI	*m_pManager;		// 父窗体的CPaintManagerUI，用来获取素材资源和父窗体句柄
	HWND			 m_hWnd;			// 阴影窗体的句柄
	LONG			 m_OriParentProc;	// 子类化父窗体
	BYTE			 m_Status;
	bool			 m_bIsImageMode;	// 是否为图片阴影模式
	bool			 m_bIsShowShadow;	// 是否要显示阴影

	// 算法阴影成员变量
	unsigned char m_nDarkness;	// Darkness, transparency of blurred area
	unsigned char m_nSharpness;	// Sharpness, width of blurred border of shadow window
	signed char m_nSize;	// Shadow window size, relative to parent window size

	// The X and Y offsets of shadow window,
	// relative to the parent window, at center of both windows (not top-left corner), signed
	signed char m_nxOffset;
	signed char m_nyOffset;

	// Restore last parent window size, used to determine the update strategy when parent window is resized
	LPARAM m_WndSize;

	// Set this to true if the shadow should not be update until next WM_PAINT is received
	bool m_bUpdate;

	COLORREF m_Color;	// Color of shadow

	// 图片阴影成员变量
	CDuiString	m_sShadowImage;
	RECT		m_rcShadowCorner;
};

}

#endif //__UISHADOW_H__

       UIShadow.cpp源码为：

#include "StdAfx.h"
#include "UIShadow.h"
#include "math.h"
#include "crtdbg.h"
#include "Core/UIManager.h"

namespace DuiLib
{

const TCHAR *strWndClassName = _T("PerryShadowWnd");
std::map<HWND, CShadowUI *>* CShadowUI::s_Shadowmap = new std::map<HWND, CShadowUI *>;
bool CShadowUI::s_bHasInit = FALSE;

CShadowUI::CShadowUI(void)
: m_hWnd((HWND)NULL)
, m_OriParentProc(NULL)
, m_nDarkness(150)
, m_nSharpness(5)
, m_nSize(0)
, m_nxOffset(0)
, m_nyOffset(0)
, m_Color(RGB(0, 0, 0))
, m_WndSize(0)
, m_bUpdate(false)
, m_bIsImageMode(false)
, m_bIsShowShadow(false)
{
	::ZeroMemory(&m_rcShadowCorner, sizeof(RECT));
}

CShadowUI::~CShadowUI(void)
{
}

bool CShadowUI::Initialize(HINSTANCE hInstance)
{
	if (s_bHasInit)
		return false;

	// Register window class for shadow window
	WNDCLASSEX wcex;

	memset(&wcex, 0, sizeof(wcex));

	wcex.cbSize = sizeof(WNDCLASSEX);
	wcex.style			= CS_HREDRAW | CS_VREDRAW;
	wcex.lpfnWndProc	= DefWindowProc;
	wcex.cbClsExtra		= 0;
	wcex.cbWndExtra		= 0;
	wcex.hInstance		= hInstance;
	wcex.hIcon			= NULL;
	wcex.hCursor		= LoadCursor(NULL, IDC_ARROW);
	wcex.hbrBackground	= (HBRUSH)(COLOR_WINDOW+1);
	wcex.lpszMenuName	= NULL;
	wcex.lpszClassName	= strWndClassName;
	wcex.hIconSm		= NULL;

	RegisterClassEx(&wcex);

	s_bHasInit = true;
	return true;
}

void CShadowUI::Create(CPaintManagerUI* pPaintManager)
{
	if(!m_bIsShowShadow)
		return;

	// Already initialized
	_ASSERT(CPaintManagerUI::GetInstance() != INVALID_HANDLE_VALUE);
	_ASSERT(pPaintManager != NULL);
	m_pManager = pPaintManager;
	HWND hParentWnd = m_pManager->GetPaintWindow();
	// Add parent window - shadow pair to the map
	_ASSERT(s_Shadowmap->find(hParentWnd) == s_Shadowmap->end());	// Only one shadow for each window
	(*s_Shadowmap)[hParentWnd] = this;

	// Determine the initial show state of shadow according to parent window's state
	LONG lParentStyle = GetWindowLong(hParentWnd, GWL_STYLE);

	// Create the shadow window
	LONG styleValue = lParentStyle & WS_CAPTION;
	m_hWnd = CreateWindowEx(WS_EX_LAYERED | WS_EX_TRANSPARENT, strWndClassName, NULL,
		/*WS_VISIBLE | */styleValue | WS_POPUPWINDOW,
		CW_USEDEFAULT, 0, 0, 0, hParentWnd, NULL, CPaintManagerUI::GetInstance(), NULL);

	if(!(WS_VISIBLE & lParentStyle))	// Parent invisible
		m_Status = SS_ENABLED;
	else if((WS_MAXIMIZE | WS_MINIMIZE) & lParentStyle)	// Parent visible but does not need shadow
		m_Status = SS_ENABLED | SS_PARENTVISIBLE;
	else	// Show the shadow
	{
		m_Status = SS_ENABLED | SS_VISABLE | SS_PARENTVISIBLE;
		::ShowWindow(m_hWnd, SW_SHOWNA);
		Update(hParentWnd);
	}

	// Replace the original WndProc of parent window to steal messages
	m_OriParentProc = GetWindowLong(hParentWnd, GWL_WNDPROC);

#pragma warning(disable: 4311)	// temporrarily disable the type_cast warning in Win32
	SetWindowLong(hParentWnd, GWL_WNDPROC, (LONG)ParentProc);
#pragma warning(default: 4311)

}

LRESULT CALLBACK CShadowUI::ParentProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
	_ASSERT(s_Shadowmap->find(hwnd) != s_Shadowmap->end());	// Shadow must have been attached

	CShadowUI *pThis = (*s_Shadowmap)[hwnd];

	switch(uMsg)
	{
	case WM_MOVE:
		if(pThis->m_Status & SS_VISABLE)
		{
			RECT WndRect;
			GetWindowRect(hwnd, &WndRect);
			if (pThis->m_bIsImageMode)
			{
				SetWindowPos(pThis->m_hWnd, 0,
					WndRect.left - pThis->m_rcShadowCorner.left, WndRect.top - pThis->m_rcShadowCorner.top,
					0, 0, SWP_NOSIZE | SWP_NOACTIVATE);
			}
			else
			{
				SetWindowPos(pThis->m_hWnd, 0,
					WndRect.left + pThis->m_nxOffset - pThis->m_nSize, WndRect.top + pThis->m_nyOffset - pThis->m_nSize,
					0, 0, SWP_NOSIZE | SWP_NOACTIVATE);
			}
		}
		break;

	case WM_SIZE:
		if(pThis->m_Status & SS_ENABLED)
		{
			if(SIZE_MAXIMIZED == wParam || SIZE_MINIMIZED == wParam)
			{
				::ShowWindow(pThis->m_hWnd, SW_HIDE);
				pThis->m_Status &= ~SS_VISABLE;
			}
			else if(pThis->m_Status & SS_PARENTVISIBLE)	// Parent maybe resized even if invisible
			{
				// Awful! It seems that if the window size was not decreased
				// the window region would never be updated until WM_PAINT was sent.
				// So do not Update() until next WM_PAINT is received in this case
				if(LOWORD(lParam) > LOWORD(pThis->m_WndSize) || HIWORD(lParam) > HIWORD(pThis->m_WndSize))
					pThis->m_bUpdate = true;
				else
					pThis->Update(hwnd);
				if(!(pThis->m_Status & SS_VISABLE))
				{
					::ShowWindow(pThis->m_hWnd, SW_SHOWNA);
					pThis->m_Status |= SS_VISABLE;
				}
			}
			pThis->m_WndSize = lParam;
		}
		break;

	case WM_PAINT:
		{
			if(pThis->m_bUpdate)
			{
				pThis->Update(hwnd);
				pThis->m_bUpdate = false;
			}
			//return hr;
			break;
		}

		// In some cases of sizing, the up-right corner of the parent window region would not be properly updated
		// Update() again when sizing is finished
	case WM_EXITSIZEMOVE:
		if(pThis->m_Status & SS_VISABLE)
		{
			pThis->Update(hwnd);
		}
		break;

	case WM_SHOWWINDOW:
		if(pThis->m_Status & SS_ENABLED)
		{
			if(!wParam)	// the window is being hidden
			{
				::ShowWindow(pThis->m_hWnd, SW_HIDE);
				pThis->m_Status &= ~(SS_VISABLE | SS_PARENTVISIBLE);
			}
			else if(!(pThis->m_Status & SS_PARENTVISIBLE))
			{
				//pThis->Update(hwnd);
				pThis->m_bUpdate = true;
				::ShowWindow(pThis->m_hWnd, SW_SHOWNA);
				pThis->m_Status |= SS_VISABLE | SS_PARENTVISIBLE;
			}
		}
		break;

	case WM_DESTROY:
		DestroyWindow(pThis->m_hWnd);	// Destroy the shadow
		break;

	case WM_NCDESTROY:
		s_Shadowmap->erase(hwnd);	// Remove this window and shadow from the map
		break;

	}

#pragma warning(disable: 4312)	// temporrarily disable the type_cast warning in Win32
	// Call the default(original) window procedure for other messages or messages processed but not returned
	return ((WNDPROC)pThis->m_OriParentProc)(hwnd, uMsg, wParam, lParam);
#pragma warning(default: 4312)

}

void CShadowUI::Update(HWND hParent)
{

	RECT WndRect;
	GetWindowRect(hParent, &WndRect);
	int nShadWndWid;
	int nShadWndHei;
	if (m_bIsImageMode)
	{
		if(m_sShadowImage.IsEmpty())
			return;

		nShadWndWid = WndRect.right - WndRect.left + m_rcShadowCorner.left + m_rcShadowCorner.right;
		nShadWndHei = WndRect.bottom - WndRect.top + m_rcShadowCorner.top + m_rcShadowCorner.bottom;
	}
	else
	{
		nShadWndWid = WndRect.right - WndRect.left + m_nSize * 2;
		nShadWndHei = WndRect.bottom - WndRect.top + m_nSize * 2;
	}

	// Create the alpha blending bitmap
	BITMAPINFO bmi;        // bitmap header

	ZeroMemory(&bmi, sizeof(BITMAPINFO));
	bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	bmi.bmiHeader.biWidth = nShadWndWid;
	bmi.bmiHeader.biHeight = nShadWndHei;
	bmi.bmiHeader.biPlanes = 1;
	bmi.bmiHeader.biBitCount = 32;         // four 8-bit components
	bmi.bmiHeader.biCompression = BI_RGB;
	bmi.bmiHeader.biSizeImage = nShadWndWid * nShadWndHei * 4;

	BYTE *pvBits;          // pointer to DIB section
	HBITMAP hbitmap = CreateDIBSection(NULL, &bmi, DIB_RGB_COLORS, (void **)&pvBits, NULL, 0);
	HDC hMemDC = CreateCompatibleDC(NULL);
	HBITMAP hOriBmp = (HBITMAP)SelectObject(hMemDC, hbitmap);

	if (m_bIsImageMode)
	{
		RECT rcPaint = {0, 0, nShadWndWid, nShadWndHei};

		const TImageInfo* data = m_pManager->GetImageEx((LPCTSTR)m_sShadowImage, NULL, 0);

		if( !data )
			return;    

		RECT rcBmpPart = {0};
		rcBmpPart.right = data->nX;
		rcBmpPart.bottom = data->nY;

		CRenderEngine::DrawImage(hMemDC, data->hBitmap, rcPaint, rcPaint, rcBmpPart, m_rcShadowCorner, data->alphaChannel, 0xFF, true, false, false);

	}
	else
	{
		ZeroMemory(pvBits, bmi.bmiHeader.biSizeImage);
		MakeShadow((UINT32 *)pvBits, hParent, &WndRect);
	}

	POINT ptDst;
	if (m_bIsImageMode)
	{
		ptDst.x = WndRect.left - m_rcShadowCorner.left;
		ptDst.y = WndRect.top - m_rcShadowCorner.top;
	}
	else
	{
		ptDst.x = WndRect.left + m_nxOffset - m_nSize;
		ptDst.y = WndRect.top + m_nyOffset - m_nSize;
	}

	POINT ptSrc = {0, 0};
	SIZE WndSize = {nShadWndWid, nShadWndHei};
	BLENDFUNCTION blendPixelFunction= { AC_SRC_OVER, 0, 255, AC_SRC_ALPHA };

	MoveWindow(m_hWnd, ptDst.x, ptDst.y, nShadWndWid, nShadWndHei, FALSE);

	BOOL bRet= ::UpdateLayeredWindow(m_hWnd, NULL, &ptDst, &WndSize, hMemDC,
		&ptSrc, 0, &blendPixelFunction, ULW_ALPHA);

	_ASSERT(bRet); // something was wrong....

	// Delete used resources
	SelectObject(hMemDC, hOriBmp);
	DeleteObject(hbitmap);
	DeleteDC(hMemDC);

}

void CShadowUI::MakeShadow(UINT32 *pShadBits, HWND hParent, RECT *rcParent)
{
	// The shadow algorithm:
	// Get the region of parent window,
	// Apply morphologic erosion to shrink it into the size (ShadowWndSize - Sharpness)
	// Apply modified (with blur effect) morphologic dilation to make the blurred border
	// The algorithm is optimized by assuming parent window is just "one piece" and without "wholes" on it

	// Get the region of parent window,
	HRGN hParentRgn = CreateRectRgn(0, 0, 0, 0);
	GetWindowRgn(hParent, hParentRgn);

	// Determine the Start and end point of each horizontal scan line
	SIZE szParent = {rcParent->right - rcParent->left, rcParent->bottom - rcParent->top};
	SIZE szShadow = {szParent.cx + 2 * m_nSize, szParent.cy + 2 * m_nSize};
	// Extra 2 lines (set to be empty) in ptAnchors are used in dilation
	int nAnchors = max(szParent.cy, szShadow.cy);	// # of anchor points pares
	int (*ptAnchors)[2] = new int[nAnchors + 2][2];
	int (*ptAnchorsOri)[2] = new int[szParent.cy][2];	// anchor points, will not modify during erosion
	ptAnchors[0][0] = szParent.cx;
	ptAnchors[0][1] = 0;
	ptAnchors[nAnchors + 1][0] = szParent.cx;
	ptAnchors[nAnchors + 1][1] = 0;
	if(m_nSize > 0)
	{
		// Put the parent window anchors at the center
		for(int i = 0; i < m_nSize; i++)
		{
			ptAnchors[i + 1][0] = szParent.cx;
			ptAnchors[i + 1][1] = 0;
			ptAnchors[szShadow.cy - i][0] = szParent.cx;
			ptAnchors[szShadow.cy - i][1] = 0;
		}
		ptAnchors += m_nSize;
	}
	for(int i = 0; i < szParent.cy; i++)
	{
		// find start point
		int j;
		for(j = 0; j < szParent.cx; j++)
		{
			if(PtInRegion(hParentRgn, j, i))
			{
				ptAnchors[i + 1][0] = j + m_nSize;
				ptAnchorsOri[i][0] = j;
				break;
			}
		}

		if(j >= szParent.cx)	// Start point not found
		{
			ptAnchors[i + 1][0] = szParent.cx;
			ptAnchorsOri[i][1] = 0;
			ptAnchors[i + 1][0] = szParent.cx;
			ptAnchorsOri[i][1] = 0;
		}
		else
		{
			// find end point
			for(j = szParent.cx - 1; j >= ptAnchors[i + 1][0]; j--)
			{
				if(PtInRegion(hParentRgn, j, i))
				{
					ptAnchors[i + 1][1] = j + 1 + m_nSize;
					ptAnchorsOri[i][1] = j + 1;
					break;
				}
			}
		}
	}

	if(m_nSize > 0)
		ptAnchors -= m_nSize;	// Restore pos of ptAnchors for erosion
	int (*ptAnchorsTmp)[2] = new int[nAnchors + 2][2];	// Store the result of erosion
	// First and last line should be empty
	ptAnchorsTmp[0][0] = szParent.cx;
	ptAnchorsTmp[0][1] = 0;
	ptAnchorsTmp[nAnchors + 1][0] = szParent.cx;
	ptAnchorsTmp[nAnchors + 1][1] = 0;
	int nEroTimes = 0;
	// morphologic erosion
	for(int i = 0; i < m_nSharpness - m_nSize; i++)
	{
		nEroTimes++;
		//ptAnchorsTmp[1][0] = szParent.cx;
		//ptAnchorsTmp[1][1] = 0;
		//ptAnchorsTmp[szParent.cy + 1][0] = szParent.cx;
		//ptAnchorsTmp[szParent.cy + 1][1] = 0;
		for(int j = 1; j < nAnchors + 1; j++)
		{
			ptAnchorsTmp[j][0] = max(ptAnchors[j - 1][0], max(ptAnchors[j][0], ptAnchors[j + 1][0])) + 1;
			ptAnchorsTmp[j][1] = min(ptAnchors[j - 1][1], min(ptAnchors[j][1], ptAnchors[j + 1][1])) - 1;
		}
		// Exchange ptAnchors and ptAnchorsTmp;
		int (*ptAnchorsXange)[2] = ptAnchorsTmp;
		ptAnchorsTmp = ptAnchors;
		ptAnchors = ptAnchorsXange;
	}

	// morphologic dilation
	ptAnchors += (m_nSize < 0 ? -m_nSize : 0) + 1;	// now coordinates in ptAnchors are same as in shadow window
	// Generate the kernel
	int nKernelSize = m_nSize > m_nSharpness ? m_nSize : m_nSharpness;
	int nCenterSize = m_nSize > m_nSharpness ? (m_nSize - m_nSharpness) : 0;
	UINT32 *pKernel = new UINT32[(2 * nKernelSize + 1) * (2 * nKernelSize + 1)];
	UINT32 *pKernelIter = pKernel;
	for(int i = 0; i <= 2 * nKernelSize; i++)
	{
		for(int j = 0; j <= 2 * nKernelSize; j++)
		{
			double dLength = sqrt((i - nKernelSize) * (i - nKernelSize) + (j - nKernelSize) * (double)(j - nKernelSize));
			if(dLength < nCenterSize)
				*pKernelIter = m_nDarkness << 24 | PreMultiply(m_Color, m_nDarkness);
			else if(dLength <= nKernelSize)
			{
				UINT32 nFactor = ((UINT32)((1 - (dLength - nCenterSize) / (m_nSharpness + 1)) * m_nDarkness));
				*pKernelIter = nFactor << 24 | PreMultiply(m_Color, nFactor);
			}
			else
				*pKernelIter = 0;
			//TRACE("%d ", *pKernelIter >> 24);
			pKernelIter ++;
		}
		//TRACE("\n");
	}
	// Generate blurred border
	for(int i = nKernelSize; i < szShadow.cy - nKernelSize; i++)
	{
		int j;
		if(ptAnchors[i][0] < ptAnchors[i][1])
		{

			// Start of line
			for(j = ptAnchors[i][0];
				j < min(max(ptAnchors[i - 1][0], ptAnchors[i + 1][0]) + 1, ptAnchors[i][1]);
				j++)
			{
				for(int k = 0; k <= 2 * nKernelSize; k++)
				{
					UINT32 *pPixel = pShadBits +
						(szShadow.cy - i - 1 + nKernelSize - k) * szShadow.cx + j - nKernelSize;
					UINT32 *pKernelPixel = pKernel + k * (2 * nKernelSize + 1);
					for(int l = 0; l <= 2 * nKernelSize; l++)
					{
						if(*pPixel < *pKernelPixel)
							*pPixel = *pKernelPixel;
						pPixel++;
						pKernelPixel++;
					}
				}
			}	// for() start of line

			// End of line
			for(j = max(j, min(ptAnchors[i - 1][1], ptAnchors[i + 1][1]) - 1);
				j < ptAnchors[i][1];
				j++)
			{
				for(int k = 0; k <= 2 * nKernelSize; k++)
				{
					UINT32 *pPixel = pShadBits +
						(szShadow.cy - i - 1 + nKernelSize - k) * szShadow.cx + j - nKernelSize;
					UINT32 *pKernelPixel = pKernel + k * (2 * nKernelSize + 1);
					for(int l = 0; l <= 2 * nKernelSize; l++)
					{
						if(*pPixel < *pKernelPixel)
							*pPixel = *pKernelPixel;
						pPixel++;
						pKernelPixel++;
					}
				}
			}	// for() end of line

		}
	}	// for() Generate blurred border

	// Erase unwanted parts and complement missing
	UINT32 clCenter = m_nDarkness << 24 | PreMultiply(m_Color, m_nDarkness);
	for(int i = min(nKernelSize, max(m_nSize - m_nyOffset, 0));
		i < max(szShadow.cy - nKernelSize, min(szParent.cy + m_nSize - m_nyOffset, szParent.cy + 2 * m_nSize));
		i++)
	{
		UINT32 *pLine = pShadBits + (szShadow.cy - i - 1) * szShadow.cx;
		if(i - m_nSize + m_nyOffset < 0 || i - m_nSize + m_nyOffset >= szParent.cy)	// Line is not covered by parent window
		{
			for(int j = ptAnchors[i][0]; j < ptAnchors[i][1]; j++)
			{
				*(pLine + j) = clCenter;
			}
		}
		else
		{
			for(int j = ptAnchors[i][0];
				j < min(ptAnchorsOri[i - m_nSize + m_nyOffset][0] + m_nSize - m_nxOffset, ptAnchors[i][1]);
				j++)
				*(pLine + j) = clCenter;
			for(int j = max(ptAnchorsOri[i - m_nSize + m_nyOffset][0] + m_nSize - m_nxOffset, 0);
				j < min(ptAnchorsOri[i - m_nSize + m_nyOffset][1] + m_nSize - m_nxOffset, szShadow.cx);
				j++)
				*(pLine + j) = 0;
			for(int j = max(ptAnchorsOri[i - m_nSize + m_nyOffset][1] + m_nSize - m_nxOffset, ptAnchors[i][0]);
				j < ptAnchors[i][1];
				j++)
				*(pLine + j) = clCenter;
		}
	}

	// Delete used resources
	delete[] (ptAnchors - (m_nSize < 0 ? -m_nSize : 0) - 1);
	delete[] ptAnchorsTmp;
	delete[] ptAnchorsOri;
	delete[] pKernel;
	DeleteObject(hParentRgn);
}

void CShadowUI::ShowShadow(bool bShow)
{
	m_bIsShowShadow = bShow;
}

bool CShadowUI::IsShowShadow() const
{
	return m_bIsShowShadow;
}

bool CShadowUI::SetSize(int NewSize)
{
	if(NewSize > 20 || NewSize < -20)
		return false;

	m_nSize = (signed char)NewSize;
	if(m_hWnd != NULL && (SS_VISABLE & m_Status))
		Update(GetParent(m_hWnd));
	return true;
}

bool CShadowUI::SetSharpness(unsigned int NewSharpness)
{
	if(NewSharpness > 20)
		return false;

	m_nSharpness = (unsigned char)NewSharpness;
	if(m_hWnd != NULL && (SS_VISABLE & m_Status))
		Update(GetParent(m_hWnd));
	return true;
}

bool CShadowUI::SetDarkness(unsigned int NewDarkness)
{
	if(NewDarkness > 255)
		return false;

	m_nDarkness = (unsigned char)NewDarkness;
	if(m_hWnd != NULL && (SS_VISABLE & m_Status))
		Update(GetParent(m_hWnd));
	return true;
}

bool CShadowUI::SetPosition(int NewXOffset, int NewYOffset)
{
	if(NewXOffset > 20 || NewXOffset < -20 ||
		NewYOffset > 20 || NewYOffset < -20)
		return false;

	m_nxOffset = (signed char)NewXOffset;
	m_nyOffset = (signed char)NewYOffset;
	if(m_hWnd != NULL && (SS_VISABLE & m_Status))
		Update(GetParent(m_hWnd));
	return true;
}

bool CShadowUI::SetColor(COLORREF NewColor)
{
	m_Color = NewColor;
	if(m_hWnd != NULL && (SS_VISABLE & m_Status))
		Update(GetParent(m_hWnd));
	return true;
}

bool CShadowUI::SetImage(LPCTSTR szImage)
{
	if (szImage == NULL)
		return false;

	m_bIsImageMode = true;
	m_sShadowImage = szImage;
	if(m_hWnd != NULL && (SS_VISABLE & m_Status))
		Update(GetParent(m_hWnd));

	return true;
}
bool CShadowUI::SetShadowCorner(RECT rcCorner)
{
	if (rcCorner.left < 0 || rcCorner.top < 0 || rcCorner.right < 0 || rcCorner.bottom < 0)
		return false;

	m_rcShadowCorner = rcCorner;

	if(m_hWnd != NULL && (SS_VISABLE & m_Status))
		Update(GetParent(m_hWnd));

	return true;
}

} //namespace DuiLib

总结：

这个阴影使用双层窗体实现的，可以避免duilib在半透明窗体上的不足。但也由于使用双层窗体，导致窗体大小快速改变时会看出阴影改变的延迟 ，能不能接受这个延迟就看个人了，所以如果是固定大小的窗体使用阴影效果最好。具体的效果可以看我的demo。

完整的修改版的库代码和阴影的demo，可以下载我的库：点击打开链接