Round corner key box in gnuplot

In a previous post I talked about create a round corner rectangle in gnuplot. But none application was involved in that post. Today I use the method to create a round corner key box.

###############################################
#Variables:
##(a,b) is the low left vertex of the rectangle
##(c,d) is the up right vertex of the rectangle
##rx is the radius along x-axis
##ry is the radius along y-axis
##x is the independent variable of the curve
f_low(a,b,c,d,rx,ry,x)=a<x && x<a+rx ? \
     -ry*sqrt(1-((x-a-rx)/rx)**2)+b+ry : \
     a+rx<x && x<c-rx ? b :c-rx<x && x<c ?\
     -ry*sqrt(1-((x-c+rx)/rx)**2)+b+ry : 1/0
#The low curve of a round corner rectangle
f_up(a,b,c,d,rx,ry,x)=a<x && x<a+rx ?\
     ry*sqrt(1-((x-a-rx)/rx)**2)+d-ry : \
     a+rx<x && x<c-rx ? d :c-rx<x && x<c ?\
     ry*sqrt(1-((x-c+rx)/rx)**2)+d-ry : 1/0
#The up curve of a round corner rectangle
###############################################
reset
set term png font "Times,18"    #terminal and output file
set output "round_corner_rectangle_key_box.png"
set tics out nomirror
unset key    #key will be created manually
set sample 1000    #samples
#Setting the back ground color
set object 1 rect from graph 0,0 to graph 1,1 back
set object 1 rect fc rgb "#AAAAFF" fillstyle solid 1.0
#The text of the key (some people call it legend)
set label center "y=f(x)" at 5.75,0.7 front
#x and y label
set xlabel "x"
set ylabel "y=f(x)"
#Plot the curve,round corner rectangle and sample line of key
plot sin(5.*x)*exp(-x*x/20.) w l lw 2 lc rgb"green",\
     '+' u 1:(f_low(3.5,0.5,9,0.9,0.5,0.05,$1)):\
     (f_up(3.5,0.5,9,0.9,0.5,0.05,$1)) w filledcurve\
     lc rgb"pink" notitle,\
     x>7.5 && x<8.5 ?0.7:1/0 w l lw 2 lc rgb"green"

Nothing new in this script. The only important and difficult thing is deciding the position of the key text, key sample line and key box. At last we get a picture like this one.

Round corner key box in gnuplot