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# GFR Rettangoli.

# Rettangolo come c(bs,bd,ad,as)
# per poter applicare polygon.
Gfr = function (dx=NA,dy=NA,
  x1=NA,x2=NA,y1=NA,y2=NA,centro=NA)
{if (P.def(centro))
{x=Re(centro); y=Im(centro)
x1=x-dx/2; x2=x+dx/2
y1=y-dy/2; y2=y+dy/2}
else if (P.def(x1,y1,dx,dy))
{x2=x1+dx; y2=y1+dy}
else if (P.def(x1,y2,dx,dy))
{x2=x1+dx; y1=y2-dy}
else if (P.def(x2,y1,dx,dy))
{x1=x2-dx; y2=y1+dy}
else if (P.def(x2,y2,dx,dy))
{x1=x2-dx; y1=y2-dy}
bs=x1+1i*y1; bd=x2+1i*y1
as=x1+1i*y2; ad=x2+1i*y2
c(bs,bd,ad,as)}

Gfr.centro = function (r) (r[1]+r[3])/2

Gfr.dx = function (r) Re(r[2]-r[1])

Gfr.dy = function (r) Im(r[3]-r[2])

Gfr.x1 = function (r) Re(r[1])

Gfr.x2 = function (r) Re(r[2])

Gfr.y1 = function (r) Im(r[1])

Gfr.y2 = function (r) Im(r[3])