How-to draw using "canvas_item_add_triangle_array" ?

I am currently facing a roadblock preventing me to draw custom triangulated polygons.

a little background:
i got some vector data containing lots polygons from all kinds of sizes, so large, it's even exceeding the compatibility mode's 'item_buffer_size'.
But that aside i found that when adding a dense polygon using the Polygon2D node or RenderServer-canvas_item_add_polygon, the application would hang. so i timed the functions and found that for a PackedVector2Array consisting of 32173 point, took nearly 16 seconds to triangulate! so this made me decide to create a gdextension that will provide triangulation methods from delaunator-cpp and that reduced the processing time to 32ms!!. so now i triangulated the polygon using a different way, but i had no idea to actually draw this triangulated polyon. so ofcourse with today's AI i found out about RenderServer canvas_item_add_triangle_array so i ended up with the following code

func poly_to_render(polygon: PackedVector2Array, parentn: Node, color: Color):
	var startt = Time.get_ticks_msec()
	var indices = Delaunay.triangulate(polygon) # our gdextension

	var pi_rid = RenderingServer.canvas_item_create()
	RenderingServer.canvas_item_set_parent(pi_rid, parentn.get_canvas_item())

	var colors = PackedColorArray()
	colors.append(color)

	var uvs = PackedVector2Array()

	if indices.size() % 3 == 0: #Make sure the triangulation was successful
		print("Adding polygon!")
		RenderingServer.canvas_item_add_triangle_array(pi_rid, indices, polygon, colors)

	var endt = Time.get_ticks_msec()
	print("Finished Poly To Render / Duration: ", endt - startt, " Amount of points: ", polygon.size())

altough the code runs without errors, this time it won't draw. what am i missing ?