漸變填充

一、通過劃分成小個矩形進行漸變填充

	CRect rectangle;
	//分割客戶區域成小矩形，逐個填充
	for (int i = x1; i < x2; i++)
	{
		rectangle.SetRect(i, y1, i + 1, y2);
		m_pDC->FillSolidRect(&rectangle, RGB(255, 255, 255 - MulDiv(i, 255, x2-x1)));
	}