The efficiency of Geometry2D polygon offset with JOIN_ROUND operation has slowed down significantly in 4.3

[mikhaelmartin]

Tested versions

4.3.stable

System information

Godot v4.3.stable - Fedora Linux 40 (Workstation Edition) - X11 - GLES3 (Compatibility) - AMD Radeon Graphics (radeonsi, renoir, LLVM 18.1.6, DRM 3.57, 6.10.12-200.fc40.x86_64) - AMD Ryzen 7 5700G with Radeon Graphics (16 Threads)

Issue description

My game use Geometry2D.polygon_offset heavily in animating polygons. i need it to be executed each frame for several polygons. After updating from Godot 4.2.2 to 4.3 I noticed significant performance hit.
This performance hit is only when using Geometry2D.polygon_offset with JOIN_ROUND.

I believe this is related to recent update from clipper1 to clipper2 library #90153

my testing with the same input polygon the resulting offset has significantly more points, could be due to precision change.

code for test:

extends Polygon2D

# Called when the node enters the scene tree for the first time.
func _ready() -> void:
	var poly = polygon
	prints("input polygon:",poly,"\n")
	
	var poly_offset = []
	
	var start_time = Time.get_ticks_usec()
	for i in 10000:
		poly_offset = Geometry2D.offset_polygon(poly,10,Geometry2D.JOIN_ROUND)
	prints("4.3 offset join round:")
	prints("execution time:", Time.get_ticks_usec() - start_time)
	prints("result size:",poly_offset[0].size(),"\n")
	
	start_time = Time.get_ticks_usec()
	for i in 10000:
		poly_offset = Geometry2D.offset_polygon(poly,10,Geometry2D.JOIN_MITER)
	prints("4.3 offset join miter:")
	prints("execution time:", Time.get_ticks_usec() - start_time)
	prints("result size:",poly_offset[0].size(),"\n")

	polygon = poly_offset[0]

result from 4.2:

result from 4.3:

For compatibility reason, new polygon_offset should have the same precision with previous godot version. Or even better expose precision as an option argument to polygon_offset

Steps to reproduce

• execute Geometry2d.polygon_offset with JOIN_ROUND as argument

Minimal reproduction project (MRP)

geometry 2d test 4.2.zip
geometry 2d test 4.3.zip

[AThousandShips]

CC @rburing