void edge_d(double x1, double y1,
double x2, double y2)
{
if (m_Rasterizer.sorted()) reset();
m_VectorClipper.move_to(m_VectorClipper.upscale(x1), m_VectorClipper.upscale(y1));
m_VectorClipper.line_to(m_Rasterizer,
m_VectorClipper.upscale(x2),
m_VectorClipper.upscale(y2));
}