metapost 宏用于绘制实心圆不起作用

Question

以下宏仅在第一次调用时绘制一个黑色圆圈。其余三个圆圈未填充。我哪里做错了？

def big(expr z) = 
begingroup
save a;
path a;
a = fullcircle scaled 3mm;
fill a withcolor black;
draw a shifted z;
endgroup
enddef;

beginfig(1)

big(origin); %black circle drawn
big((1cm,0)); % unfilled circle
big((2.5cm,0)); % unfilled circle
big((3cm,0)); % unfilled circle

endfig;
end;

Answer 1

第一个命令

fill a withcolor black;

绘制一个以原点为中心的实心圆。第二个命令

draw a shifted z;

绘制移动了 的圆z。您想要的是也移动实心圆：

fill a shifted z withcolor black;
draw a shifted z;

或者更简单地说：

def big(expr z) = 
    begingroup
    save a; path a;
    a = fullcircle shifted z scaled 3mm;
    fill a withcolor black;
    draw a;
    endgroup
enddef;