/*

so, we have a line.

from 0,0 to 10,0

and we want it to transform into a rectangle at about...

-1,-1 1,-1 1,11 -1,11

I guess we're taking each point and pushing it away from itself.

so 0,0... we can make into a square. we need to push in a direction based on the direction of the other half of the line

so a=points_to_angle(p1,p2)

which is 90deg in this case from 0,0 to 10,0
and we need to push 0,0 in two directions to create two new points
at angles...
90+135 and 90+135+90

a+135 and a+135+90

now to pick an emboldeness amount. sqrt(2) will get us to the original points I guessed at earlier.

#define embolden(p1,p2,angle,dist) 

if(s.len == 2) {
 a1=points_to_angle(p1,p2);
 a2=points_to_angle(p2,p1);
 d=1;//how far to embolden
 //a2 = (a1 + 180) % 360
 s[0]=c3_add(s.p[0],(c3_t){sin(a2+45)*d,cos(a2+45)*d,0})
 s[1]=c3_add(s.p[0],(c3_t){sin(a2-45)*d,cos(a2-45)*d,0})
 s[2]=c3_add(s.p[1],(c3_t){sin(a1+45)*d,cos(a1+45)*d,0})
 s[3]=c3_add(s.p[1],(c3_t){sin(a1-45)*d,cos(a1-45)*d,0})
}

//this can be a script. it'll turn lines into rectangles.
//could be done with awk probably.
//base it on offsetshape?
//maybe just do it in python.