使用 metapost 填充曲线之间的区域

Question

我怎样才能填充 p2 和 p3 之间的区域？我尝试使用buildcycle宏，但没有用。

path p[];
p1 = fullcircle xscaled 1.2in yscaled 0.6in;

p2 = (-1cm, 0)..(0cm, -0.2cm)..(1cm, 0) shifted up;
p3 = p2 rotatedaround(center p1, 180) shifted down cutbefore p2 cutafter p2;

fill buildcycle(p2, p3) withcolor red;

draw p1 scaled 1.2; draw p2 scaled 1.2;
draw p3 scaled 1.2;

Answer 1

buildcycle在修剪之前使用p3- 否则它们不会重叠，正如错误消息所说的那样。

这是一个包含其他一些建议的优化的版本。

prologues := 3;
outputtemplate := "%j%c.%{outputformat}";
beginfig(1);
path p[];
p1 = fullcircle xscaled 1.2in yscaled 0.6in;
p2 = (-1cm, 0)..(0cm, -0.2cm)..(1cm, 0) shifted up;
p3 = p2 rotatedaround(center p1, 180) shifted down;
% scale all the paths
for i=1,2,3: p[i] := p[i] scaled 2; endfor

% now make the path round the middle
fill buildcycle(p2, p3) withcolor red;

% now trim the upper path
p3 := p3 cutbefore p2 cutafter p2;

% finally draw them all.
draw p1; 
draw p2;
draw p3;

endfig;
end.

使用 进行编译mpost，然后使用epstopdf或类似的工具来获得以下内容：

Answer 2

fill buildcycle(reverse p2, p3) scaled 1.2 withcolor red;