4

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：当我运行我的函数来绘制一个稍微透明的矩形时，它没有显示在我的窗口上。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什么才能让我的函数在窗口上绘制一个稍微透明的矩形吗？

我也知道 GDI+，但我现在想避免它，因为我在使用该库时遇到了很多编译/包含错误，而且我想在没有库的帮助的情况下尽可能低/原生我。

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;
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2 回答 2

5

这将起作用：

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)); 
}
于 2012-06-11T06:54:24.873 回答
3

CreateCompatibleDC 函数返回一个兼容的 dc，其默认位图大小为 1x1。为了画出有用的东西，首先你应该选择一个更合适的大小合适的位图。您可以使用CreateCompatibleBitmap函数。

基本上你应该做这样的事情：

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;

但认真地你应该重新考虑 GDI+，试着找出为什么你有所有这些编译器错误并修复它们。GDI 非常老旧，不太友好，需要手动管理资源，使用起来相当痛苦。

祝你好运。

于 2012-06-11T06:40:22.660 回答