半透明或过滤某种颜色的实现

BOOL SetLayeredWindowAttributes(
　HWND hwnd, // handle to the layered window
　COLORREF crKey, // specifies the color key
　BYTE bAlpha, // value for the blend function
　DWORD dwFlags // action
);

Windows NT/2000/XP: Included in Windows 2000 and later.
Windows 95/98/Me: Unsupported.
Header: Declared in Winuser.h; include Windows.h.
Library: Use User32.lib.

　　一些常量:

　　WS_EX_LAYERED = 0x80000;
　　LWA_ALPHA = 0x2;
　　LWA_COLORKEY=0x1

　　其中dwFlags有LWA_ALPHA和LWA_COLORKEY。LWA_ALPHA被设置的话,通过bAlpha决定透明度，LWA_COLORKEY被设置的话,则指定被透明掉的颜色为crKey，其他颜色则正常显示。

　　注:要使使窗体拥有透明效果，首先要有WS_EX_LAYERED扩展属性(旧sdk也没有的)。 　
　
　　例子代码:

　　在OnInitDialog()加入:
　
//加入WS_EX_LAYERED扩展属性
SetWindowLong(this->GetSafeHwnd(),GWL_EXSTYLE,
GetWindowLong(this->GetSafeHwnd(),GWL_EXSTYLE)^0x80000);
HINSTANCE hInst = LoadLibrary("User32.DLL");
if(hInst)
{
　typedef BOOL (WINAPI *MYFUNC)(HWND,COLORREF,BYTE,DWORD);
　MYFUNC fun = NULL;
　//取得SetLayeredWindowAttributes函数指针
　fun=(MYFUNC)GetProcAddress(hInst, "SetLayeredWindowAttributes");
　if(fun)fun(this->GetSafeHwnd(),0,128,2);
　FreeLibrary(hInst);
}

第二种例子代码
在.h中加入
#define LWA_COLORKEY 0x00000001
#define WS_EX_LAYERED 0x00080000
typedef BOOL (WINAPI *lpfnSetLayeredWindowAttributes)(HWND hWnd, COLORREF crKey, BYTE bAlpha, DWORD dwFlags);
lpfnSetLayeredWindowAttributes SetLayeredWindowAttributes;

在.cpp中
COLORREF maskColor=RGB(0X80,0XC0,0XFF);
HMODULE hUser32 = GetModuleHandle("user32.dll");
SetLayeredWindowAttributes = (lpfnSetLayeredWindowAttributes)GetProcAddress(hUser32,"SetLayeredWindowAttributes");
SetWindowLong(GetSafeHwnd(), GWL_EXSTYLE, GetWindowLong(GetSafeHwnd(), GWL_EXSTYLE)|WS_EX_LAYERED);
SetLayeredWindowAttributes(GetSafeHwnd(), maskColor, 255, LWA_COLORKEY);
FreeLibrary(hUser32);