BasicFit, a curve fitting algorithm to generate a Bézier Curve from my Polygon2D brush

renevanderark · May 19, 2026, 1:29pm

While it is currently under review by insert name here ;-), I would like to share my latest work here; just for funzies.

Mind you, I’m not a mathematician by any means, but you still might have a very good purpose for this curve-fitting algorithm somewhere in your game. I dubbed it BasicFit, because that’s a pun when you live in a country that has that fitness franchise:

github.com/Teaching-myself-Godot/ez-curved-lines-2d

addons/curved_lines_2d/basic_fit.gd

05ef27d2d

@tool
class_name BasicFit
extends Object

const MAX_ANGLE_INBOUND_TO_OUTBOUND := deg_to_rad(30.0)
const MAX_CUMULATIVE_ANGLE_PER_SEGMENT := deg_to_rad(90.0)


static func prepare_polyline_segments(pts : PackedVector2Array, snap := 10.0,
		max_ang := MAX_ANGLE_INBOUND_TO_OUTBOUND, max_cum_ang := MAX_CUMULATIVE_ANGLE_PER_SEGMENT) -> Array[int]:
	if pts.size() < 4:
		return [0]
	var splits : Array[int] = [0]
	## any point p of which the angle between the inbound and outbound line p_a exceeds 30.0° will
	## become the start of a new segment
	for i in range(1, pts.size()):
		var prev_p := pts[i - 1]
		var p := pts[i]
		var next_p := pts[i + 1] if i < pts.size() - 1 else pts[0]
		if absf(prev_p.direction_to(p).angle_to(p.direction_to(next_p))) > max_ang:

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Aside from BasicFit (currently under review), I’ve also been wanting to talk about Geometry2DUtil, which I’ve been using to make it more easy to cut holes, detect closest points on the line segment of Curve2D and similar stuff:

github.com/Teaching-myself-Godot/ez-curved-lines-2d

addons/curved_lines_2d/geometry_2d_util.gd

05ef27d2d

@tool
extends Object
class_name Geometry2DUtil

const THRESHOLD = 0.1

static func get_polygon_bounding_rect(points : PackedVector2Array) -> Rect2:
	var minx := INF
	var miny := INF
	var maxx := -INF
	var maxy := -INF
	for p : Vector2 in points:
		minx = p.x if p.x < minx else minx
		miny = p.y if p.y < miny else miny
		maxx = p.x if p.x > maxx else maxx
		maxy = p.y if p.y > maxy else maxy
	return Rect2(minx, miny, maxx - minx, maxy - miny)


static func get_polygon_center(points : PackedVector2Array) -> Vector2:

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I ship these classes under MIT license, for what that’s worth… Here’s hoping it makes someone here a little happy!

dragonforge-dev · May 19, 2026, 2:00pm

Those are cool, I’m just not sure what I would use them with.

renevanderark · May 19, 2026, 2:43pm

You never know. I use it for painting fills, strokes and collision polygons.

You could calculate a Path2D around a dynamically generated island too, I guess.

Think of it like this. If someone searches the web for this stuff, now there’s a bigger chance to find it via the forum.

dragonforge-dev · May 19, 2026, 4:34pm

It reminds me a lot of the Gravity Ace level editor, shown in the second video. I just found this the other day, and it’s really cool. So it could be used for something like that.

renevanderark · May 19, 2026, 4:43pm

Thing is. Scalable Vector Shapes 2D became a big solve the world plugin, showcased mostly for art drawing in engine… But if I were an experienced game dev I would probably want to just cherry pick some useful stuff and not have a big old dependency added to my project.

Also. I just want to make the flash games I used to play online, and make games fit any screen without blur or raspy edges.. and x and y and solve the world.