agg_math_stroke.h

windows ce 下的画各种b样条曲线

                //-----------------
                add_vertex(vc, v1.x + dx1, v1.y - dy1);
                miter_limit_exceeded = false;
            }
        }

        if(miter_limit_exceeded)
        {
            // Miter limit exceeded
            //------------------------
            switch(lj)
            {
            case miter_join_revert:
                // For the compatibility with SVG, PDF, etc, 
                // we use a simple bevel join instead of
                // "smart" bevel
                //-------------------
                add_vertex(vc, v1.x + dx1, v1.y - dy1);
                add_vertex(vc, v1.x + dx2, v1.y - dy2);
                break;

            case miter_join_round:
                calc_arc(vc, v1.x, v1.y, dx1, -dy1, dx2, -dy2);
                break;

            default:
                // If no miter-revert, calculate new dx1, dy1, dx2, dy2
                //----------------
                if(intersection_failed)
                {
                    mlimit *= m_width_sign;
                    add_vertex(vc, v1.x + dx1 + dy1 * mlimit, 
                                   v1.y - dy1 + dx1 * mlimit);
                    add_vertex(vc, v1.x + dx2 - dy2 * mlimit, 
                                   v1.y - dy2 - dx2 * mlimit);
                }
                else
                {
                    double x1 = v1.x + dx1;
                    double y1 = v1.y - dy1;
                    double x2 = v1.x + dx2;
                    double y2 = v1.y - dy2;
                    di = (lim - dbevel) / (di - dbevel);
                    add_vertex(vc, x1 + (xi - x1) * di, 
                                   y1 + (yi - y1) * di);
                    add_vertex(vc, x2 + (xi - x2) * di, 
                                   y2 + (yi - y2) * di);
                }
                break;
            }
        }
    }

    //--------------------------------------------------------stroke_calc_cap
    template<class VC> 
    void math_stroke<VC>::calc_cap(VC& vc,
                                   const vertex_dist& v0, 
                                   const vertex_dist& v1, 
                                   double len)
    {
        vc.remove_all();

        double dx1 = (v1.y - v0.y) / len;
        double dy1 = (v1.x - v0.x) / len;
        double dx2 = 0;
        double dy2 = 0;

        dx1 *= m_width;
        dy1 *= m_width;

        if(m_line_cap != round_cap)
        {
            if(m_line_cap == square_cap)
            {
                dx2 = dy1 * m_width_sign;
                dy2 = dx1 * m_width_sign;
            }
            add_vertex(vc, v0.x - dx1 - dx2, v0.y + dy1 - dy2);
            add_vertex(vc, v0.x + dx1 - dx2, v0.y - dy1 - dy2);
        }
        else
        {
            double da = acos(m_width_abs / (m_width_abs + 0.125 / m_approx_scale)) * 2;
            double a1;
            int i;
            int n = int(pi / da);

            da = pi / (n + 1);
            add_vertex(vc, v0.x - dx1, v0.y + dy1);
            if(m_width_sign > 0)
            {
                a1 = atan2(dy1, -dx1);
                a1 += da;
                for(i = 0; i < n; i++)
                {
                    add_vertex(vc, v0.x + cos(a1) * m_width, 
                                   v0.y + sin(a1) * m_width);
                    a1 += da;
                }
            }
            else
            {
                a1 = atan2(-dy1, dx1);
                a1 -= da;
                for(i = 0; i < n; i++)
                {
                    add_vertex(vc, v0.x + cos(a1) * m_width, 
                                   v0.y + sin(a1) * m_width);
                    a1 -= da;
                }
            }
            add_vertex(vc, v0.x + dx1, v0.y - dy1);
        }
    }

    //-----------------------------------------------------------------------
    template<class VC> 
    void math_stroke<VC>::calc_join(VC& vc,
                                    const vertex_dist& v0, 
                                    const vertex_dist& v1, 
                                    const vertex_dist& v2,
                                    double len1, 
                                    double len2)
    {
        double dx1 = m_width * (v1.y - v0.y) / len1;
        double dy1 = m_width * (v1.x - v0.x) / len1;
        double dx2 = m_width * (v2.y - v1.y) / len2;
        double dy2 = m_width * (v2.x - v1.x) / len2;

        vc.remove_all();

        double cp = cross_product(v0.x, v0.y, v1.x, v1.y, v2.x, v2.y);
        if(cp != 0 && (cp > 0) == (m_width > 0))
        {
            // Inner join
            //---------------
            double limit = ((len1 < len2) ? len1 : len2) / m_width_abs;
            if(limit < m_inner_miter_limit)
            {
                limit = m_inner_miter_limit;
            }

            switch(m_inner_join)
            {
            default: // inner_bevel
                add_vertex(vc, v1.x + dx1, v1.y - dy1);
                add_vertex(vc, v1.x + dx2, v1.y - dy2);
                break;

            case inner_miter:
                calc_miter(vc,
                           v0, v1, v2, dx1, dy1, dx2, dy2, 
                           miter_join_revert, 
                           limit, 0);
                break;

            case inner_jag:
            case inner_round:
                cp = (dx1-dx2) * (dx1-dx2) + (dy1-dy2) * (dy1-dy2);
                if(cp < len1 * len1 && cp < len2 * len2)
                {
                    calc_miter(vc,
                               v0, v1, v2, dx1, dy1, dx2, dy2, 
                               miter_join_revert, 
                               limit, 0);
                }
                else
                {
                    if(m_inner_join == inner_jag)
                    {
                        add_vertex(vc, v1.x + dx1, v1.y - dy1);
                        add_vertex(vc, v1.x,       v1.y      );
                        add_vertex(vc, v1.x + dx2, v1.y - dy2);
                    }
                    else
                    {
                        add_vertex(vc, v1.x + dx1, v1.y - dy1);
                        add_vertex(vc, v1.x,       v1.y      );
                        calc_arc(vc, v1.x, v1.y, dx2, -dy2, dx1, -dy1);
                        add_vertex(vc, v1.x,       v1.y      );
                        add_vertex(vc, v1.x + dx2, v1.y - dy2);
                    }
                }
                break;
            }
        }
        else
        {
            // Outer join
            //---------------

            // Calculate the distance between v1 and 
            // the central point of the bevel line segment
            //---------------
            double dx = (dx1 + dx2) / 2;
            double dy = (dy1 + dy2) / 2;
            double dbevel = sqrt(dx * dx + dy * dy);

            if(m_line_join == round_join || m_line_join == bevel_join)
            {
                // This is an optimization that reduces the number of points 
                // in cases of almost collinear segments. If there's no
                // visible difference between bevel and miter joins we'd rather
                // use miter join because it adds only one point instead of two. 
                //
                // Here we calculate the middle point between the bevel points 
                // and then, the distance between v1 and this middle point. 
                // At outer joins this distance always less than stroke width, 
                // because it's actually the height of an isosceles triangle of
                // v1 and its two bevel points. If the difference between this
                // width and this value is small (no visible bevel) we can 
                // add just one point. 
                //
                // The constant in the expression makes the result approximately 
                // the same as in round joins and caps. You can safely comment 
                // out this entire "if".
                //-------------------
                if(m_approx_scale * (m_width_abs - dbevel) < m_width_eps)
                {
                    if(calc_intersection(v0.x + dx1, v0.y - dy1,
                                         v1.x + dx1, v1.y - dy1,
                                         v1.x + dx2, v1.y - dy2,
                                         v2.x + dx2, v2.y - dy2,
                                         &dx, &dy))
                    {
                        add_vertex(vc, dx, dy);
                    }
                    else
                    {
                        add_vertex(vc, v1.x + dx1, v1.y - dy1);
                    }
                    return;
                }
            }

            switch(m_line_join)
            {
            case miter_join:
            case miter_join_revert:
            case miter_join_round:
                calc_miter(vc, 
                           v0, v1, v2, dx1, dy1, dx2, dy2, 
                           m_line_join, 
                           m_miter_limit,
                           dbevel);
                break;

            case round_join:
                calc_arc(vc, v1.x, v1.y, dx1, -dy1, dx2, -dy2);
                break;

            default: // Bevel join
                add_vertex(vc, v1.x + dx1, v1.y - dy1);
                add_vertex(vc, v1.x + dx2, v1.y - dy2);
                break;
            }
        }
    }




}

#endif