如何在DC上绘制上百万级的点

// 绘制轨迹图像
void CImageLayerView::DrawTrackImage(CDC& dc_)
{
	if (m_vecTrackImage.empty())
	{
		return;
	}

	DWORD _dwBegin = GetTickCount();
	
	CRect _rcClient;
	GetClientRect(&_rcClient);

	BITMAP _info;
	CBitmap _bitmapTemp;
	_bitmapTemp.CreateBitmap(_rcClient.Width(), _rcClient.Height(), 1, 32, NULL);

	_bitmapTemp.GetBitmap(&_info);

	CBitmap _bitmap;
	CDC _dcMemory;  
	const int c_nSize = _rcClient.Width() * _rcClient.Height()*4;
	BYTE* _pBits = (BYTE*)new BYTE[c_nSize];
	//::ZeroMemory(_pBits, c_nSize); 
	memset(_pBits, 0xffffffff, _rcClient.Width() * _rcClient.Height()*4);

	/*for (int i = 0;i < _info.bmWidth;++i)  
	{  
		for (int j = 0;j < _info.bmHeight;++j)  
		{  
			_pBits[i * 4 + j * _info.bmWidthBytes + 2] = 0;
			_pBits[i * 4 + j * _info.bmWidthBytes + 1] = 0;
			_pBits[i * 4 + j * _info.bmWidthBytes + 0] = 255;
		}
	} */

	
	for (int _j=0; _j<int(m_vecTrackImage.size()); _j++)
	{
		for (int _k=0;_k<int(m_vecTrackImage[_j].vecImageColor.size()); _k++)
		{
				FCDoub2D _pt;
				//_pt.x = m_vecTrackImage[_j].vecImageColor[_k].x;
				//_pt.y = m_vecTrackImage[_j].vecImageColor[_k].y;
				//
				_pt.x = _rcClient.right * m_fScale - (m_vecTrackImage[_j].vecImageColor[_k].x * m_fScale - m_ptMoveOffst.x);
				_pt.y = _rcClient.bottom * m_fScale - (m_vecTrackImage[_j].vecImageColor[_k].y * m_fScale - m_ptMoveOffst.y);


				if (_pt.x < 0. || 
					_pt.y < 0. ||
					_pt.x > _info.bmWidth ||
					_pt.y > _info.bmHeight)
				{
					continue;
				}

				_pBits[int(_pt.x) * 4 + int(_pt.y) * _info.bmWidthBytes + 2] = GetRValue(m_vecTrackImage[_j].vecImageColor[_k].color);
				_pBits[int(_pt.x) * 4 + int(_pt.y) * _info.bmWidthBytes + 1] = GetGValue(m_vecTrackImage[_j].vecImageColor[_k].color);
				_pBits[int(_pt.x) * 4 + int(_pt.y) * _info.bmWidthBytes + 0] = GetBValue(m_vecTrackImage[_j].vecImageColor[_k].color);
		}
	}

	DWORD _dwEnd = GetTickCount() - _dwBegin;

	_bitmap.CreateBitmap(_rcClient.Width(), _rcClient.Height(), 1, 32, _pBits);
	_bitmap.SetBitmapBits(c_nSize, _pBits); 
	_dcMemory.CreateCompatibleDC(&dc_); 

	CBitmap *pbmpOld = _dcMemory.SelectObject(&_bitmap);  
	dc_.BitBlt(0, 0, _rcClient.Width(), _rcClient.Height(), &_dcMemory, 0, 0, SRCCOPY);  
	_dcMemory.SelectObject(pbmpOld); 

	delete _pBits;
	_pBits = NULL;
}