void edge(int x1, int y1, int x2, int y2)
{
if (m_Rasterizer.sorted()) reset();
m_VectorClipper.move_to(m_VectorClipper.downscale(x1), m_VectorClipper.downscale(y1));
m_VectorClipper.line_to(m_Rasterizer,
m_VectorClipper.downscale(x2),
m_VectorClipper.downscale(y2));
}