par("uin") ? / brace function

The following works for me:

brace <- function (x1 = 0, y1 = 0, x2 = 0, y2 = 1, right = TRUE, rad = 
0.2)
{
   uin<-xyinch() # thanks to Paul's comment; I had forgotten xinch()
   ux <- uin[1]
   uy <- uin[2]
   dx <- x2 - x1
   dy <- y2 - y1
   alpha <- atan2(ux * dx, uy * dy)  # in R, we need atan2()
   scale <- sqrt((ux * dx)^2 + (uy * dy)^2)
   if (scale > 5 * rad)
       rad <- rad/scale
   qcirc <- cbind(cos((0:10) * pi/20), sin((0:10) * pi/20))
   qcircr <- cbind(cos((10:0) * pi/20), sin((10:0) * pi/20))
   rot <- function(theta) t(cbind(c(cos(theta), sin(theta)),
       c(-sin(theta), cos(theta))))
   seg1 <- t(t(rad * qcirc %*% rot(-pi/2)) + c(0, rad))
   seg4 <- t(t(rad * qcirc) + c(0, 1 - rad))
   seg3 <- t(t((rad * qcircr) %*% rot(pi)) + c(2 * rad, 0.5 +
       rad))
   seg2 <- t(t((rad * qcircr) %*% rot(pi/2)) + c(2 * rad, 0.5 -
       rad))
   bra <- rbind(seg1, seg2, seg3, seg4)
   if (!right)
       bra <- bra %*% diag(c(-1, 1))
   bra <- scale * bra %*% rot(-alpha)
   bra <- bra %*% diag(c(1/ux, 1/uy))
   bra <- t(t(bra) + c(x1, y1))
   bra
}

plot(...)
lines(brace(...))

For non-vertical/horizontal braces, the arcs at the ends
don't seem quite right to me. Also, it would seem useful
to be able to just define the cusp and the width of a
brace. I might have a look at that over the weekend.

 -Peter Ehlers


On 2010-07-19 9:20, Michael Friendly wrote:

I inherited a function written either for an older version of R or SPlus
to draw a brace, "{", in a graph. It uses par("uin") to determine the
scaling of the
quarter circles that make up segments of the brace, but that setting
doesn't
exist in current R.
I'm guessing that, in the function below, ux, uy can be defined from
par("usr") and par("pin"), but maybe someone remembers what par("uin")
was supposed to refer to.

brace <- function (x1 = 0, y1 = 0, x2 = 0, y2 = 1, right = TRUE, rad 
= 0.2)
{

[....]