![在 metapost 中获取笔划的路径](https://linux22.com/image/369713/%E5%9C%A8%20metapost%20%E4%B8%AD%E8%8E%B7%E5%8F%96%E7%AC%94%E5%88%92%E7%9A%84%E8%B7%AF%E5%BE%84.png)
假设我有一些相当简单的 metapost 代码:
outputformat := "svg";
outputtemplate := "%j-%c.svg";
beginfig(1);
pickup pencircle scaled .2in yscaled .2 rotated 30;
u := 36;
z0 = (0,0);
z1 = (0,1u);
z2 = (1u,0);
z3 = (0,-1u);
z4 = (-1u,0);
draw z1 -- z3 withcolor .7white;
draw z2 -- z4 withcolor .7white;
dotlabels.top(0,1,2,3,4);
endfig;
end
这将输出一个与原点相交的十字图形z0
。
仅作为说明性示例,假设我想使两个笔画之间的交点变得平滑:我需要两个笔画之间的交点,然后是沿路径的点,如下所示:
红点为交点,蓝点为笔触路径。
我觉得如果能够获得笔触的路径,那么实现我的想法就非常容易了。
答案1
下面是如何使用 new 运算符的示例envelope
。
outputformat := "svg";
outputtemplate := "%j-%c.svg";
beginfig(1);
% pickup pencircle scaled .2in yscaled .2 rotated 30;
% this only works with a polygonal pen, so lets make a close approximation to pencircle...
pen knib;
knib = makepen((for t=0 upto 30: right scaled 7.2 rotated 12t -- endfor cycle) yscaled 1/5 rotated 30);
pickup knib;
u := 36;
z0 = (0,0);
z1 = (0,1u);
z2 = (1u,0);
z3 = (0,-1u);
z4 = (-1u,0);
draw z1 -- z3 withcolor .7white;
draw z2 -- z4 withcolor .7white;
% switch back to the default pen
pickup defaultpen;
draw envelope knib of (z1--z3) withcolor red;
draw envelope knib of (z2--z4) withcolor blue;
dotlabels.top(0,1,2,3,4);
endfig;
end.
这产生了这个(剪辑和字体由 imagemagick 提供...):
这或多或少是 OP 想要的。
下一步是将返回的路径保存envelope
为path
变量,并用它intersectionpoint
来查找它们的交叉点。您可能需要明智地使用subpath
来获得所需的准确交叉点。
我正在使用 MP 2.000
toby$ mpost --v
MetaPost 2.000 (TeX Live 2017) (kpathsea version 6.2.3)
The MetaPost source code in the public domain.
MetaPost also uses code available under the
GNU Lesser General Public License (version 3 or later);
therefore MetaPost executables are covered by the LGPL.
There is NO warranty.
For more information about these matters, see the file
COPYING.LESSER or <http://gnu.org/licenses/lgpl.html>.
Original author of MetaPost: John Hobby.
Author of the CWEB MetaPost: Taco Hoekwater.
Current maintainer of MetaPost: Luigi Scarso.
Compiled with cairo 1.14.8; using 1.14.8
Compiled with pixman 0.34.0; using 0.34.0
Compiled with libpng 1.6.29; using 1.6.29
Compiled with zlib 1.2.11; using 1.2.11
Compiled with mpfr 3.1.5; using 3.1.5
Compiled with gmp 6.1.2; using 6.1.2