使用MFC实现上面的按钮半透明效果能看到父窗口中的内容，上面是效果图(一个是带背景图片的、另一个是不带的)。
控件继承自CWnd类(彩色的部分是窗口的背景图片、按钮是PNG图片，第二个图标是鼠标指向时的效果)。
图标的绘制使用GDI+绘制PNG图片，在此不多说了(处理WM_PAINT消息):
1 void PNGButton::OnPaint()
2 {
3 CPaintDC dc(this);
4 Graphics g(dc.m_hDC);
5 if(DrawBorder){
6 g.DrawImage(hoverBg,0,0);//画鼠标指向时的亮色背景
7 }
8 g.DrawImage(this->bg,0,0);//画按钮图标
9 g.ReleaseHDC(dc.m_hDC);
10 }
透明的关键：注意后面调用此方法的代码
关键在于InvalidateRect函数:通知父窗口重新绘制特定区域,执行此函数后按钮所在区域就被父窗口绘制的内容覆盖.在父窗口绘制完成后,
按钮也会收到WM_PAINT消息,执行上面的一段OnPaint代码.
1 void PNGButton::PaintParent()
2 {
3 CRect rect;
4 GetWindowRect(&rect);
5 GetParent()-> ScreenToClient(&rect);
6 GetParent()-> InvalidateRect(&rect);
7 }
捕获鼠标指向或移出事件(处理WM_MOUSEMOVE,WM_MOUSEOVER,WM_MOUSELEAVE消息)：
1 void PNGButton::OnMouseHover(UINT nFlags, CPoint point)
2 {
3 DrawBorder=true;
4 PaintParent();//通知父窗口重绘特定区域，会引发控件自身的重绘
5 }
6
7
8 void PNGButton::OnMouseLeave()
9 {
10 m_is_mouse_over = false;
11 m_is_tracked = false;
12 DrawBorder=false;
13 PaintParent(); //通知父窗口重绘特定区域，会引发控件自身的重绘
14 CWnd::OnMouseLeave();
15 }
16
17
18 void PNGButton::OnMouseMove(UINT nFlags, CPoint point)
19 {
20 m_is_mouse_over = true;
21 if(!m_is_tracked)
22 {
23 TRACKMOUSEEVENT tme;
24 tme.cbSize = sizeof(TRACKMOUSEEVENT);
25 tme.dwFlags = TME_LEAVE|TME_HOVER;
26 tme.hwndTrack = GetSafeHwnd();
27 tme.dwHoverTime = 80;
28 _TrackMouseEvent(&tme);
29 m_is_tracked = true;
30 }
31 CWnd::OnMouseMove(nFlags, point);
32 }
附：
从资源加载PNG图片
1 #pragma once
2 #include "stdafx.h"
3 using namespace Gdiplus;
4
5 static bool ImageFromIDResource(UINT nID, LPCTSTR sTR,Image * &pImg)
6 {
7 HINSTANCE hInst = AfxGetResourceHandle();
8 HRSRC hRsrc = ::FindResource (hInst,MAKEINTRESOURCE(nID),sTR); // type
9 if (!hRsrc)
10 return FALSE;
11 // load resource into memory
12 DWORD len = SizeofResource(hInst, hRsrc);
13 BYTE* lpRsrc = (BYTE*)LoadResource(hInst, hRsrc);
14 if (!lpRsrc)
15 return FALSE;
16 // Allocate global memory on which to create stream
17 HGLOBAL m_hMem = GlobalAlloc(GMEM_FIXED, len);
18 BYTE* pmem = (BYTE*)GlobalLock(m_hMem);
19 memcpy(pmem,lpRsrc,len);
20 IStream* pstm;
21 CreateStreamOnHGlobal(m_hMem,FALSE,&pstm);
22 // load from stream
23 pImg=Gdiplus::Image::FromStream(pstm);
24 // free/release stuff
25 GlobalUnlock(m_hMem);
26 pstm->Release();
27 FreeResource(lpRsrc);
28 return TRUE;
29 }
平铺图片的代码
1 CPaintDC dc(this);
2 CRect rect;
3 GetClientRect(rect);
4 CBrush bs(RGB(240,240,240));//窗口背景色
5 dc.FillRect(&rect,&bs); //窗口着色
6 //填充背景图片：平铺
7 Graphics g(dc.m_hDC);
8 if(has_bg) g.DrawImage(this->bg,0,0);
9 Gdiplus::TextureBrush bbs(this->img);
10 g.FillRectangle(&bbs,0,0,rect.Width(),this->img->GetHeight());
11 g.ReleaseHDC(dc.m_hDC);
12 //TRACE(L"CMainFrame::OnPaint\r\n");