title: Using AlphaBlend to draw slightly transparent rectangle fails
body: <p>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. </p>
  
  <p><strong>My Problem:</strong> 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?</p>
  
  <p><strong>Can you tell me what I need to do to get my function to draw a slightly transparent rectangle on the window?</strong></p>
  
  <p><em>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.</em></p>
  
  <pre><code>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, &amp;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, &amp;ps);
  }
  break;
  </code></pre>