使用AlphaBlend绘制略微透明的矩形失败

Question

我试图在Native Win32 C++中绘制一个稍微透明的蓝色矩形.我正在使用函数AlphaBlend()但它没有在窗口上绘制任何东西,没有任何反应.

我的问题:当我运行我的函数绘制一个稍微透明的矩形时,它不会显示在我的窗口上.我有一种感觉我做错了,也许我应该使用HBITMAP？

你能告诉我我需要做些什么来让我的功能在窗口上绘制一个稍微透明的矩形吗？

我也知道GDI +,但我现在想要避免使用它,因为当我使用该库时我会得到很多编译/包含错误,而且我希望尽可能低或原生,而不需要库的帮助.我.

bool paintRect(HDC hdc, RECT dim, COLORREF penCol, COLORREF brushCol, unsigned int opacity)
{
    HDC tempHdc         = CreateCompatibleDC(hdc);
    BLENDFUNCTION blend = {AC_SRC_OVER, 0, 127, AC_SRC_ALPHA};

    SetDCPenColor(tempHdc, RGB(255,255,0));
    SetDCBrushColor(tempHdc, RGB(255,255,0));
    Rectangle(tempHdc, dim.left, dim.top, dim.right, dim.bottom);

    return bool(AlphaBlend(hdc, dim.left, dim.top, dim.right, dim.bottom, tempHdc, dim.left, dim.top, dim.right, dim.bottom, blend)); 
}
// Usage
case WM_PAINT:
{
   HDC hdc;
   PAINTSTRUCT ps;
   hdc = BeginPaint(hwnd, &ps);

   RECT a = {0,0,100,100};
   paintRect(hdc, a, RGB(255,255,0), RGB(255,255,0), 127); // 127 is 50% transparency right?

   EndPaint(hwnd, &ps);
}
break;

Answer 1

这将有效:

bool paintRect(HDC hdc, RECT dim, COLORREF penCol, COLORREF brushCol, unsigned int opacity)
{
        HDC tempHdc         = CreateCompatibleDC(hdc);
        BLENDFUNCTION blend = {AC_SRC_OVER, 0, 127, 0};

        HBITMAP hbitmap;       // bitmap handle 
        BITMAPINFO bmi;        // bitmap header 
        // zero the memory for the bitmap info 
        ZeroMemory(&bmi, sizeof(BITMAPINFO));

        // setup bitmap info  
        // set the bitmap width and height to 60% of the width and height of each of the three horizontal areas. Later on, the blending will occur in the center of each of the three areas. 
        bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
        bmi.bmiHeader.biWidth = dim.right-dim.left;
        bmi.bmiHeader.biHeight = dim.bottom-dim.top;
        bmi.bmiHeader.biPlanes = 1;
        bmi.bmiHeader.biBitCount = 32;         // four 8-bit components 
        bmi.bmiHeader.biCompression = BI_RGB;
        bmi.bmiHeader.biSizeImage = (dim.right-dim.left) * (dim.bottom-dim.top) * 4;

        // create our DIB section and select the bitmap into the dc 
        hbitmap = CreateDIBSection(tempHdc, &bmi, DIB_RGB_COLORS, NULL, NULL, 0x0);
        SelectObject(tempHdc, hbitmap);

        SetDCPenColor(tempHdc, RGB(0,0,255));
        SetDCBrushColor(tempHdc, RGB(0,0,255));
        FillRect(tempHdc, &dim, CreateSolidBrush(RGB(0,0,255)));

        return bool(AlphaBlend(hdc, dim.left, dim.top, dim.right, dim.bottom, tempHdc, dim.left, dim.top, dim.right, dim.bottom, blend)); 
}