MFC中透明位图原理

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总之，就是不断反复遮罩“过滤掉”透明色就行，先来整段代码，后面再详细介绍。

void CTransDlg::OnPaint() {CPaintDC dc(this);CMemDC m_dc;if(!m_dc)m_dc.LoadBitmap(IDB_BITMAP4);CMemDC dcImage(100,100,&dc);CBitmap bmpMask;bmpMask.CreateBitmap(100,100,1,1,NULL);CDC dcMask;dcMask.CreateCompatibleDC(&dc);dcMask.SelectObject(bmpMask);dcImage.BitBlt(0,0,100,100,&m_dc,0,0,SRCCOPY);dc.BitBlt(10,10,100,100,&m_dc,0,0,SRCCOPY);         //显示图1dc.BitBlt(120,10,100,100,&dcMask,0,0,SRCCOPY);      //显示图2dcImage.SetBkColor(RGB(255,0,0));dcMask.BitBlt(0,0,100,100,&dcImage,0,0,SRCCOPY);dc.BitBlt(230,10,100,100,&dcMask,0,0,SRCCOPY);      //显示图3dc.BitBlt(340,10,100,100,&dcImage,0,0,SRCCOPY);      //显示图4dcImage.SetBkColor(RGB(0,0,0));dcImage.SetTextColor(RGB(255,255,255));dc.BitBlt(450,10,100,100,&dcImage,0,0,SRCCOPY);//显示图5dcImage.BitBlt(0,0,100,100,&dcMask,0,0,SRCAND);dc.BitBlt(10,120,100,100,&dcImage,0,0,SRCCOPY);//显示图6dc.BitBlt(120,120,100,100,&dcMask,0,0,SRCCOPY);//显示图7dc.SetBkColor(RGB(255,255,255));dc.BitBlt(230,120,100,100,&dcMask,0,0,SRCAND);//显示图8dc.BitBlt(230,120,100,100,&dcImage,0,0,SRCPAINT);//显示图8}

m_dc.LoadBitmap(IDB_BITMAP4);     //加载原图，就是下面这张，由红，绿，黄组成的，白色的是背景，不算原图

CMemDC dcImage(100,100,&dc);//演示原理中一共用到了三个DC，DC就理解成一张画布，dcImage是一个临时DC，也可以理解成为一张100X100的临时画布，原图没有这么大，所以会露出背景；

CBitmap bmpMask;

CBitmap bmpMask;bmpMask.CreateBitmap(100,100,1,1,NULL);    //创建一张单色位图，位图要想看到，必须画在画布上，也就是复制到（BitBlt）DC上CDC dcMask;dcMask.CreateCompatibleDC(&dc);           //创建一张掩码用的画布dcMask.SelectObject(bmpMask);             //把那张单色位图画在画布上dcImage.BitBlt(0,0,100,100,&m_dc,0,0,SRCCOPY);   //m_dc这张画布上的原图COPY到临时画布dcImage上<pre name="code" class="cpp">dc.BitBlt(10,10,100,100,&m_dc,0,0,SRCCOPY);         //在最终画布dc上显示原图dc.BitBlt(120,10,100,100,&dcMask,0,0,SRCCOPY);      //在最终画布dc上显示单色掩码位图

dcImage.SetBkColor(RGB(255,0,0));              //把红色设置成dcImage这张画布的背景色，也就是透明色dcMask.BitBlt(0,0,100,100,&dcImage,0,0,SRCCOPY); //dcImage把自己复制给dcMask时，告诉他红色是背景色，dcMask只能显示两种颜色，所以dcImage上红色的地方变白色，其他地方是黑色dc.BitBlt(230,10,100,100,&dcMask,0,0,SRCCOPY);      //显示dcMask这张画布dc.BitBlt(340,10,100,100,&dcImage,0,0,SRCCOPY);      //显示显示dcImage这张画布

dcImage.SetBkColor(RGB(0,0,0));              //dcImage将黑色设置成背景色dcImage.SetTextColor(RGB(255,255,255));dc.BitBlt(450,10,100,100,&dcImage,0,0,SRCCOPY);//显示dcImage

dcImage.BitBlt(0,0,100,100,&dcMask,0,0,SRCAND);//dcImage与dcMask相与，注意此时dcImage的透明色是黑色，所以dcMask中的黑色到了dcImage上就成了透明色dc.BitBlt(10,120,100,100,&dcImage,0,0,SRCCOPY);//显示dcImagedc.BitBlt(120,120,100,100,&dcMask,0,0,SRCCOPY);//显示dcMask  第一张是原来的dcImage,第二张是dcMask，第三张是相与以后的dcImage

dc.SetBkColor(RGB(255,255,255));<span style="white-space:pre"></span>//最终画布dc的透明色设置成白色dc.BitBlt(230,120,100,100,&dcMask,0,0,SRCAND);//dcMask与最终画布相与dc.BitBlt(230,120,100,100,&dcImage,0,0,SRCPAINT);//dcImage与最终画布相或   第一张是dcMask,第二张是dcImage，第三张是最终效果

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