在外网上看到了一篇关于透明位图的问题，但有一些地方不明白。望高手指点。
原文如下：
包含透明色的位图的绘制方法有多种，最简单的方法是调用现成的函数：TransparentBlt,也可以通过自己的代码实现类似TransparentBlt的功能，实现过程也有两种形式，一种是事先做一张掩码位图，另一种是动态生成掩码位图。本文将介绍动态生成掩码位图绘制具有透明区域位图的方法。

为了理解具有透明色位图的绘制过程，我们来亲手建立一个具有同TransparentBlt功能一致的实验函数，称之为TransparentBlt2。

实验素材：有两张位图：bk.bmp是背景位图，football.bmp包含透明区域，透明色为蓝色RGB(0,0,0xff)
实验目的：以bk.bmp为背景，将football.bmp绘制到背景中，形成如下的最终效果图。

[attachment=869801]


2.1 透明位图绘制原理
假设football.bmp ->载入 HBITMAP hImageBMP -> 选入 HDC hImageDC

2.1.1 生成足球的单色掩码位图，透明区域为白色（全1），非透明区域为黑色（全0) HBITMAP hMaskBMP = CreateBitmap(nWidthDest, nHeightDest, 1, 1, NULL); // 建立单色位图
SetBkColor(hImageDC, RGB(0,0,0xff)); // 设置背景色为蓝色
BitBlt(hMaskDC, 0, 0, nWidthDest, nHeightDest, hImageDC, 0, 0, SRCCOPY); // 拷贝到hMaskDC
这样足球位图中蓝色区域在掩码位图中成了白色，其它区域为黑色，此时hMaskBMP 如下图:
[attachment=869802] (图一)

2.1.2 设置背景色为黑色，前景色为白色，将掩码位图(图一)与足球位图相"与" SetBkColor(hImageDC, RGB(0,0,0));
SetTextColor(hImageDC, RGB(255,255,255));
BitBlt(hImageDC, 0, 0, nWidthDest, nHeightDest, hMaskDC, 0, 0, SRCAND);

这样，掩码位图中背景色（黑色）的区域在hImageBMP中被保留，前景色（白色）的部分变为黑色。 此时hImageBMP 如下图:
[attachment=869803] (图二)

2.1.3 设置背景色为白色，前景色为黑色，将掩码位图(图一)与背景进行“与”运算
SetBkColor(hdcDest,RGB(255,255,255));
SetTextColor(hdcDest,RGB(0,0,0));
BitBlt(hdcDest, nXOriginDest, nYOriginDest, nWidthDest, nHeightDest, hMaskDC, 0, 0, SRCAND);
掩码中白色区域（数据与1相“与”结果不变）使背景保持不变，黑色区域变成黑色，此时背景显示如下:
[attachment=869804] (图三)

2.1.4 将hImageBMP(图二)与背景(图三)进行“或”运算 BitBlt(hdcDest, nXOriginDest, nYOriginDest, nWidthDest, nHeightDest, hImageDC, 0, 0, SRCPAINT);
这样就将足球绘制到背景上了。

问题：这里，生成图一（掩码图）的原理我基本上搞清楚了，但是在生成图二和图三之前，为什么要先那样设置前景色和背景色就不明白了。望高手指点一二


[ 此贴被albert在2007-01-13 22:46重新编辑 ]

我一直还以为图像叠加起来是异或运算呢

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Quote:

引用第0楼albert于2007-01-13 22:33发表的[提问]关于位图:
在外网上看到了一篇关于透明位图的问题，但有一些地方不明白。望高手指点。
原文如下：
包含透明色的位图的绘制方法有多种，最简单的方法是调用现成的函数：TransparentBlt,也可以通过自己的代码实现类似TransparentBlt的功能，实现过程也有两种形式，一种是事先做一张掩码位图，另一种是动态生成掩码位图。本文将介绍动态生成掩码位图绘制具有透明区域位图的方法。

为了理解具有透明色位图的绘制过程，我们来亲手建立一个具有同TransparentBlt功能一致的实验函数，称之为TransparentBlt2。
.......

就是为了变于后面做运算啊，相当于一个filter

就是位运算而已。。。。没那么复杂