UpdateLayeredWindow和DrawText

Question

我正在使用UpdateLayeredWindow来显示应用程序窗口.我创建了自己的自定义按钮,我想创建自己的静态文本.问题是当我尝试在hdc上绘制文本时,DrawText或TextOut函数会覆盖我图片的alpha通道,文本将变为透明.我试图找到解决方案,但我找不到任何解决方案.我的自定义控件的设计方式使它们可以在名为Draw(HDC hDc)的成员函数中完成所有绘图,因此它们只能访问hdc.我想保留这个设计.谁能帮我？我正在使用MFC,我希望在不使用GDI +的情况下实现所需的结果.

Answer 1

我知道这是一个很老的帖子......但我只是遇到了同样的问题...而且它让我疯狂.

最后,我在近7年前偶然发现了Mike Sutton发给microsoft.public.win32.programmer.gdi新闻组的这篇文章!

基本上,DrawText(和TextOut)不能很好地与alpha通道和UpdateLayeredWindow一起使用...... 你需要用alpha通道预乘R,G和B通道.

在迈克的帖子中,他展示了他如何创建另一个DIB(设备无关位图),并在其上绘制文本......并且alpha将其混合到另一个位图中.

这样做之后,我的文字看起来很完美!

以防万一,新闻组帖子的链接死了......我将在这里包含代码.所有功劳都归功于Mike Sutton(@mikedsutton).

下面是创建带有文本的alpha混合位图的代码:

HBITMAP CreateAlphaTextBitmap(LPCSTR inText, HFONT inFont, COLORREF inColour)
{ 
    int TextLength = (int)strlen(inText); 
    if (TextLength <= 0) return NULL; 

    // Create DC and select font into it 
    HDC hTextDC = CreateCompatibleDC(NULL); 
    HFONT hOldFont = (HFONT)SelectObject(hTextDC, inFont); 
    HBITMAP hMyDIB = NULL; 

    // Get text area 
    RECT TextArea = {0, 0, 0, 0}; 
    DrawText(hTextDC, inText, TextLength, &TextArea, DT_CALCRECT); 
    if ((TextArea.right > TextArea.left) && (TextArea.bottom > TextArea.top))
    { 
        BITMAPINFOHEADER BMIH; 
        memset(&BMIH, 0x0, sizeof(BITMAPINFOHEADER)); 
        void *pvBits = NULL; 

        // Specify DIB setup 
        BMIH.biSize = sizeof(BMIH); 
        BMIH.biWidth = TextArea.right - TextArea.left; 
        BMIH.biHeight = TextArea.bottom - TextArea.top; 
        BMIH.biPlanes = 1; 
        BMIH.biBitCount = 32; 
        BMIH.biCompression = BI_RGB; 

        // Create and select DIB into DC 
        hMyDIB = CreateDIBSection(hTextDC, (LPBITMAPINFO)&BMIH, 0, (LPVOID*)&pvBits, NULL, 0); 
        HBITMAP hOldBMP = (HBITMAP)SelectObject(hTextDC, hMyDIB); 
        if (hOldBMP != NULL)
        { 
            // Set up DC properties 
            SetTextColor(hTextDC, 0x00FFFFFF); 
            SetBkColor(hTextDC, 0x00000000); 
            SetBkMode(hTextDC, OPAQUE); 

            // Draw text to buffer 
            DrawText(hTextDC, inText, TextLength, &TextArea, DT_NOCLIP); 
            BYTE* DataPtr = (BYTE*)pvBits; 
            BYTE FillR = GetRValue(inColour); 
            BYTE FillG = GetGValue(inColour); 
            BYTE FillB = GetBValue(inColour); 
            BYTE ThisA; 
            for (int LoopY = 0; LoopY < BMIH.biHeight; LoopY++) { 
                for (int LoopX = 0; LoopX < BMIH.biWidth; LoopX++) { 
                    ThisA = *DataPtr; // Move alpha and pre-multiply with RGB 
                    *DataPtr++ = (FillB * ThisA) >> 8; 
                    *DataPtr++ = (FillG * ThisA) >> 8; 
                    *DataPtr++ = (FillR * ThisA) >> 8; 
                    *DataPtr++ = ThisA; // Set Alpha 
                } 
            } 

            // De-select bitmap 
            SelectObject(hTextDC, hOldBMP); 
        } 
    } 

    // De-select font and destroy temp DC 
    SelectObject(hTextDC, hOldFont); 
    DeleteDC(hTextDC); 

    // Return DIBSection 
    return hMyDIB; 
}

以下是驱动CreateAlphaTextBitmap方法的代码:

void TestAlphaText(HDC inDC, int inX, int inY)
{ 
    const char *DemoText = "Hello World!\0"; 
    RECT TextArea = {0, 0, 0, 0}; 
    HFONT TempFont = CreateFont(50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "Arial\0"); 
    HBITMAP MyBMP = CreateAlphaTextBitmap(DemoText, TempFont, 0xFF); 
    DeleteObject(TempFont); 
    if (MyBMP)
    {
        // Create temporary DC and select new Bitmap into it 
        HDC hTempDC = CreateCompatibleDC(inDC); 
        HBITMAP hOldBMP = (HBITMAP)SelectObject(hTempDC, MyBMP); 
        if (hOldBMP)
        {
            // Get Bitmap image size
            BITMAP BMInf;
            GetObject(MyBMP, sizeof(BITMAP), &BMInf); 

            // Fill blend function and blend new text to window 
            BLENDFUNCTION bf; 
            bf.BlendOp = AC_SRC_OVER; 
            bf.BlendFlags = 0; 
            bf.SourceConstantAlpha = 0x80; 
            bf.AlphaFormat = AC_SRC_ALPHA; 
            AlphaBlend(inDC, inX, inY, BMInf.bmWidth, BMInf.bmHeight, hTempDC, 0, 0, BMInf.bmWidth, BMInf.bmHeight, bf); 

            // Clean up 
            SelectObject(hTempDC, hOldBMP); 
            DeleteObject(MyBMP); 
            DeleteDC(hTempDC); 
        } 
    } 
}