Error to fill non convex polygon in opengl

[GabrielLasso]

Instead it fills the convex hull of the polygon

Example:

import drawim

proc draw() =
  background(220)
  fill(255,0,0)
  beginFilledShape()

  vertex(100, 100)
  vertex(300, 300)
  vertex(500, 100)
  vertex(300, 200)

  endFilledShape()

run(600, 400, draw)

In js it works

[GabrielLasso]

https://www.flipcode.com/archives/Efficient_Polygon_Triangulation.shtml

This might work, and the code is clean. Saving here to study it later