Tri_cont
The following code:
import gr
import sequtils, sugar, math, random
let n = 100
var x = newSeq[float](n)
var y = newSeq[float](n)
var z = newSeq[float](n)
for i in 0..<n:
x[i] = 8.0 * rand(1.0) - 4.0
y[i] = 8.0 * rand(1.0) - 4.0
z[i] = sin(x[i]) + cos(y[i])
tri_cont(x,y,z)
discard readLine(stdin)
grm_finalize()
creates the following window: