c++ - 使用 BitBlt 获取另一个窗口的单个像素

Question

这是我目前正在做的:

• 通过GetWindowDC获取窗口DC
• 使用 CreateCompatibleDC 创建一个兼容的 DC
• 在我的兼容 DC 上调用 GetPixel

不幸的是，我所有的 GetPixel 调用都返回 CLR_INVALID。这是我的代码。

bool Gameboard::Refresh()
{
  bool  ret = false;
  HDC   context, localContext;

  context = GetWindowDC(m_window);
  if (context != NULL)
  {
    localContext = CreateCompatibleDC(context);
    if (localContext != NULL)
    {
      if (BitBlt(localContext, 0, 0, GameboardInfo::BoardWidth, GameboardInfo::BoardHeight,
        context, GameboardInfo::TopLeft.x, GameboardInfo::TopLeft.y, SRCCOPY))
      {
        ret = true;
        // several calls to GetPixel which all return CLR_INVALID
      }
      DeleteDC(localContext);
    }
    ReleaseDC(m_window, context);
  }
  return ret;
}

有什么想法吗？

Answer 1

我相信您需要在您的设备环境中选择一个位图。

“必须在设备上下文中选择位图，否则，将在所有像素上返回 CLR_INVALID。” - GetPixel()

bool Gameboard::Refresh()
{
  bool  ret = false;
  HDC   context, localContext;


  HGDIOBJ origHandle;


  context = GetWindowDC(m_window);
  if (context != NULL)
  {
    localContext = CreateCompatibleDC(context);


    origHandle = SelectObject(localcontext,CreateCompatibleBitmap(context, GameboardInfo::BoardWidth, GameboardInfo::BoardHeight));


    if (localContext != NULL)
    {
      if (BitBlt(localContext, 0, 0, GameboardInfo::BoardWidth, GameboardInfo::BoardHeight,
        context, GameboardInfo::TopLeft.x, GameboardInfo::TopLeft.y, SRCCOPY))
      {
        ret = true;
        // several calls to GetPixel which all return CLR_INVALID
      }

      SelectObject(localcontext, origHandle);


      DeleteDC(localContext);
    }
    ReleaseDC(m_window, context);
  }
  return ret;
}