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画一个稍微透明的矩形吗？

我也知道GDI +，但我现在想避免使用它，因为当我使用该库时，我会收到很多编译/包含错误，而且我希望在没有帮助的情况下尽可能低/本地为我做一切的图书馆。

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)); 
}

Answer 2

CreateCompatibleDC函数返回一个兼容的dc，其中包含一个大小为1x1的defualt位图。为了首先绘制有用的东西，你应该选择一个合适大小的更合适的位图。您可以使用CreateCompatibleBitmap功能。

基本上你应该这样做：

HDC tempHdc         = CreateCompatibleDC(hdc);
// create a bitmap of a size you need, let's say it 100x100
int width = 100;
int height = 100;
HBITMAP canvas = CreateCompatibleBitmap(hdc, width, height);
// select new bitmap into context, don't forget to save old bitmap handle
HBITMAP oldBmp = SelectObject(tepmHdc, canvas);

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);

bool res = AlphaBlend(hdc, dim.left, dim.top, dim.right, dim.bottom, tempHdc, dim.left, dim.top, dim.right, dim.bottom, blend);
// reset the old bitmap
SelectObect(tempHdc, oldBmp);
// canvas is no longer needed and should be deleted to avoid GDI leaks
DeleteObject(canvas);

return res;

但严重的是你应该重新考虑GDI +，试着找出你为什么会遇到所有这些编译错误并修复它们。 GDI很老，不太友好，手动资源管理，使用起来非常痛苦。

祝你好运。

使用AlphaBlend绘制略微透明的矩形失败

2 个答案: