Error in drawing 2d polygon Invalid get index '-1' (on base: 'Array').

:information_source: Attention Topic was automatically imported from the old Question2Answer platform.
:bust_in_silhouette: Asked By primevolcano

I was following this tutorial
and have been slowly converting it to 4.0.3 for my project
But im running into the same bug “Invalid get index ‘-1’ (on base: ‘Array’).”
here is the code where it breaks

func draw_water_body():
	var curve = water_border.curve
	var points = Array(curve.get_baked_points())
	var water_polygon_points = points
	var first_index = 0
	var last_index = water_polygon_points.size()-1
	water_polygon_points.append(Vector2(water_polygon_points[last_index].x, bottom))
	water_polygon_points.append(Vector2(water_polygon_points[first_index].x, bottom))

This is the code for the water border
P.S. ‘Sorry its broken btw’

class_name SmoothPath
extends Path2D

@export var spline_length:float = 8
@export var _smooth: bool: set = smooth
@export var _straighten: bool: set = straighten
@export var color: Color = Color(1,1,1,1)
@export var width:float = 8

func straighten(value):
	if not value: return
	for i in curve.get_point_count():
		curve.set_point_in(i, Vector2())
		curve.set_point_out(i, Vector2())

func smooth(value):
	if not value: return
	var point_count = curve.get_point_count()
	for i in point_count:
		var spline = _get_spline(i)
		curve.set_point_in(i, -spline)
		curve.set_point_out(i, spline)

func _get_spline(i):
	var last_point = _get_point(i - 1)
	var next_point = _get_point(i + 1)
	var spline = last_point.direction_to(next_point) * spline_length
	return spline

func _get_point(i):
	var point_count = curve.get_point_count()
	i = wrapi(i, 0, point_count - 1)
	return curve.get_point_position(i)

func _draw():
	var points = curve.get_baked_points()
	if points:
		draw_polyline(points, Color.WHITE, 8, true)

Edited to fix forum code formatting.

jgodfrey | 2023-06-01 16:47

Just guessing, but I assume this:

var points = Array(curve.get_baked_points())

is returning an empty Array.

If that’s the case, then this:

var last_index = water_polygon_points.size()-1

Will generate a last_index value of -1.

And then this will generate the error you reported:

water_polygon_points.append(Vector2(water_polygon_points[last_index].x, bottom))

If that’s correct, then you need to determine why get_baked_points() isn’t returning anything. Are you sure the underlying curve is populated when that code is called?

jgodfrey | 2023-06-01 16:53

:bust_in_silhouette: Reply From: primevolcano

Turns out nothing is wrong
I just had to call the curve function before the body

func _physics_process(delta):
for i in springs:

var left_deltas = []
var right_deltas = []

for i in range(springs.size()):
for j in range(passes):
	for i in range(springs.size()):
		if i > 0:
			left_deltas[i] = spread * (springs[i].height - springs[i-1].height)
			springs[i-1].velocity += left_deltas[i]
		if i < springs.size() -1:
			right_deltas[i] = spread * (springs[i].height - springs[i+1].height)
			springs[i+1].velocity += right_deltas[i]

Ah, so this from above… :slight_smile:

Are you sure the underlying curve is populated when that code is called?

jgodfrey | 2023-06-02 01:07