使用AlphaBlend绘制稍微透明的矩形失败 [英] Using AlphaBlend to draw slightly transparent rectangle fails

问题描述

我试图在Native Win32 C ++中绘制一个稍微透明的蓝色矩形。我使用的功能AlphaBlend（），但它没有绘制任何东西到窗口，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，它不会显示在我的窗口。我有一个感觉，我做错了，也许我应该使用HBITMAP？

你能告诉我我需要做什么，在窗口上绘制一个稍微透明的矩形？

还有我知道GDI +，但我想避免它，

$ b

  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 ））; 
} 
 //用法
 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是50％的透明度吗？ 
 
 EndPaint（hwnd，& ps）; 
} 
 break; 
  

解决方案

这将工作：

<$ c $ p> 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; //位图句柄
BITMAPINFO bmi; // bitmap header
//零位图信息的内存
ZeroMemory（& bmi，sizeof（BITMAPINFO））;

//设置位图信息
//将位图宽度和高度设置为三个水平区域的宽度和高度的60％。之后，混合将发生在三个区域中的每一个的中心。
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; //四个8位组件
bmi.bmiHeader.biCompression = BI_RGB;
bmi.bmiHeader.biSizeImage =（dim.right-dim.left）*（dim.bottom-dim.top）* 4;

//创建我们的DIB节，并选择位图到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 ））;
}


I am attempting to draw a slightly transparent blue rectangle in Native Win32 C++. I am using the function AlphaBlend() but its not drawing anything onto the window, nothing happens.

My Problem: When I run my function to draw a slightly transparent rectangle, it doesn't get shown on my window. I have a feeling I am doing this wrong, maybe I should be using a HBITMAP?

Can you tell me what I need to do to get my function to draw a slightly transparent rectangle on the window?

Also I'm aware of GDI+ but I want to avoid it for now because I am getting alot of compile/include errors when I use that library plus I want to go as low/native as possible without the help of libraries that do everything for me.

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;

解决方案

This will work:

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)); 
}

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