Replace Bezier-rs use in the 'Offset Path' node with a Kurbo algorithm (#2596)

* minimally replace bezier-rs use in Offset Path node implementation with kurbo's API

* fix kurbo import

* refactor

* Code review

---------

Co-authored-by: indierusty <priyaayadav@gmail.com>
Co-authored-by: Keavon Chambers <keavon@keavon.com>

libraries/bezier-rs/src/subpath/solvers.rs

@@ -437,7 +437,7 @@ impl<PointId: crate::Identifier> Subpath<PointId> {
 	/// Alternatively, this can be interpreted as limiting the angle that the miter can form.
 	/// When the limit is exceeded, no manipulator group will be returned.
 	/// This value should be greater than 0. If not, the default of 4 will be used.
-	pub(crate) fn miter_line_join(&self, other: &Subpath<PointId>, miter_limit: Option<f64>) -> Option<ManipulatorGroup<PointId>> {
+	pub fn miter_line_join(&self, other: &Subpath<PointId>, miter_limit: Option<f64>) -> Option<ManipulatorGroup<PointId>> {
 		let miter_limit = match miter_limit {
 			Some(miter_limit) if miter_limit > f64::EPSILON => miter_limit,
 			_ => 4.,
@@ -491,7 +491,7 @@ impl<PointId: crate::Identifier> Subpath<PointId> {
 	/// - The `out_handle` for the last manipulator group of `self`
 	/// - The new manipulator group to be added
 	/// - The `in_handle` for the first manipulator group of `other`
-	pub(crate) fn round_line_join(&self, other: &Subpath<PointId>, center: DVec2) -> (DVec2, ManipulatorGroup<PointId>, DVec2) {
+	pub fn round_line_join(&self, other: &Subpath<PointId>, center: DVec2) -> (DVec2, ManipulatorGroup<PointId>, DVec2) {
 		let left = self.manipulator_groups[self.len() - 1].anchor;
 		let right = other.manipulator_groups[0].anchor;
 

libraries/bezier-rs/src/subpath/transform.rs

@@ -1,4 +1,5 @@
 use super::*;
+use crate::BezierHandles;
 use crate::consts::MAX_ABSOLUTE_DIFFERENCE;
 use crate::utils::{Cap, Join, SubpathTValue, TValue};
 use glam::{DAffine2, DVec2};
@@ -307,7 +308,7 @@ impl<PointId: crate::Identifier> Subpath<PointId> {
 	// at the incorrect location. This can be avoided by first trimming the two Subpaths at any extrema, effectively ignoring loopbacks.
 	/// Helper function to clip overlap of two intersecting open Subpaths. Returns an optional, as intersections may not exist for certain arrangements and distances.
 	/// Assumes that the Subpaths represents simple Bezier segments, and clips the Subpaths at the last intersection of the first Subpath, and first intersection of the last Subpath.
-	fn clip_simple_subpaths(subpath1: &Subpath<PointId>, subpath2: &Subpath<PointId>) -> Option<(Subpath<PointId>, Subpath<PointId>)> {
+	pub fn clip_simple_subpaths(subpath1: &Subpath<PointId>, subpath2: &Subpath<PointId>) -> Option<(Subpath<PointId>, Subpath<PointId>)> {
 		// Split the first subpath at its last intersection
 		let intersections1 = subpath1.subpath_intersections(subpath2, None, None);
 		if intersections1.is_empty() {
@@ -366,6 +367,7 @@ impl<PointId: crate::Identifier> Subpath<PointId> {
 			.map(|bezier| bezier.offset(distance))
 			.filter(|subpath| subpath.len() >= 2) // In some cases the reduced and scaled bézier is marked by is_point (so the subpath is empty).
 			.collect::<Vec<Subpath<PointId>>>();
+
 		let mut drop_common_point = vec![true; self.len()];
 
 		// Clip or join consecutive Subpaths

node-graph/gcore/src/vector/algorithms/mod.rs

@@ -1,2 +1,3 @@
 mod instance;
 mod merge_by_distance;
+pub mod offset_subpath;

node-graph/gcore/src/vector/algorithms/offset_subpath.rs

@@ -0,0 +1,173 @@
+use crate::vector::PointId;
+use bezier_rs::{Bezier, BezierHandles, Join, Subpath, TValue};
+
+/// Value to control smoothness and mathematical accuracy to offset a cubic Bezier.
+const CUBIC_REGULARIZATION_ACCURACY: f64 = 0.5;
+/// Accuracy of fitting offset curve to Bezier paths.
+const CUBIC_TO_BEZPATH_ACCURACY: f64 = 1e-3;
+/// Constant used to determine if `f64`s are equivalent.
+pub const MAX_ABSOLUTE_DIFFERENCE: f64 = 1e-3;
+
+fn segment_to_bezier(seg: kurbo::PathSeg) -> bezier_rs::Bezier {
+	match seg {
+		kurbo::PathSeg::Line(line) => Bezier::from_linear_coordinates(line.p0.x, line.p0.y, line.p1.x, line.p1.y),
+		kurbo::PathSeg::Quad(quad_bez) => Bezier::from_quadratic_coordinates(quad_bez.p0.x, quad_bez.p0.y, quad_bez.p1.x, quad_bez.p1.y, quad_bez.p1.x, quad_bez.p1.y),
+		kurbo::PathSeg::Cubic(cubic_bez) => Bezier::from_cubic_coordinates(
+			cubic_bez.p0.x,
+			cubic_bez.p0.y,
+			cubic_bez.p1.x,
+			cubic_bez.p1.y,
+			cubic_bez.p2.x,
+			cubic_bez.p2.y,
+			cubic_bez.p3.x,
+			cubic_bez.p3.y,
+		),
+	}
+}
+
+// TODO: Replace the implementation to use only Kurbo API.
+/// Reduces the segments of the subpath into simple subcurves, then offset each subcurve a set `distance` away.
+/// The intersections of segments of the subpath are joined using the method specified by the `join` argument.
+pub fn offset_subpath(subpath: &Subpath<PointId>, distance: f64, join: Join) -> Subpath<PointId> {
+	// An offset at a distance 0 from the curve is simply the same curve.
+	// An offset of a single point is not defined.
+	if distance == 0. || subpath.len() <= 1 || subpath.len_segments() < 1 {
+		return subpath.clone();
+	}
+
+	let mut subpaths = subpath
+			.iter()
+			.filter(|bezier| !bezier.is_point())
+			.map(|bezier| bezier.to_cubic())
+			.map(|cubic| {
+				let Bezier { start, end, handles } = cubic;
+				let BezierHandles::Cubic { handle_start, handle_end } = handles else { unreachable!()};
+
+				let cubic_bez = kurbo::CubicBez::new((start.x, start.y), (handle_start.x, handle_start.y), (handle_end.x, handle_end.y), (end.x, end.y));
+				let cubic_offset = kurbo::offset::CubicOffset::new_regularized(cubic_bez, distance, CUBIC_REGULARIZATION_ACCURACY);
+				let offset_bezpath = kurbo::fit_to_bezpath(&cubic_offset, CUBIC_TO_BEZPATH_ACCURACY);
+
+				let beziers = offset_bezpath.segments().fold(Vec::new(), |mut acc, seg| {
+					acc.push(segment_to_bezier(seg));
+					acc
+				});
+
+				Subpath::from_beziers(&beziers, false)
+			})
+			.filter(|subpath| subpath.len() >= 2) // In some cases the reduced and scaled bézier is marked by is_point (so the subpath is empty).
+			.collect::<Vec<Subpath<PointId>>>();
+
+	let mut drop_common_point = vec![true; subpath.len()];
+
+	// Clip or join consecutive Subpaths
+	for i in 0..subpaths.len() - 1 {
+		let j = i + 1;
+		let subpath1 = &subpaths[i];
+		let subpath2 = &subpaths[j];
+
+		let last_segment = subpath1.get_segment(subpath1.len_segments() - 1).unwrap();
+		let first_segment = subpath2.get_segment(0).unwrap();
+
+		// If the anchors are approximately equal, there is no need to clip / join the segments
+		if last_segment.end().abs_diff_eq(first_segment.start(), MAX_ABSOLUTE_DIFFERENCE) {
+			continue;
+		}
+
+		// Calculate the angle formed between two consecutive Subpaths
+		let out_tangent = subpath.get_segment(i).unwrap().tangent(TValue::Parametric(1.));
+		let in_tangent = subpath.get_segment(j).unwrap().tangent(TValue::Parametric(0.));
+		let angle = out_tangent.angle_to(in_tangent);
+
+		// The angle is concave. The Subpath overlap and must be clipped
+		let mut apply_join = true;
+		if (angle > 0. && distance > 0.) || (angle < 0. && distance < 0.) {
+			// If the distance is large enough, there may still be no intersections. Also, if the angle is close enough to zero,
+			// subpath intersections may find no intersections. In this case, the points are likely close enough that we can approximate
+			// the points as being on top of one another.
+			if let Some((clipped_subpath1, clipped_subpath2)) = Subpath::clip_simple_subpaths(subpath1, subpath2) {
+				subpaths[i] = clipped_subpath1;
+				subpaths[j] = clipped_subpath2;
+				apply_join = false;
+			}
+		}
+		// The angle is convex. The Subpath must be joined using the specified join type
+		if apply_join {
+			drop_common_point[j] = false;
+			match join {
+				Join::Bevel => {}
+				Join::Miter(miter_limit) => {
+					let miter_manipulator_group = subpaths[i].miter_line_join(&subpaths[j], miter_limit);
+					if let Some(miter_manipulator_group) = miter_manipulator_group {
+						subpaths[i].manipulator_groups_mut().push(miter_manipulator_group);
+					}
+				}
+				Join::Round => {
+					let (out_handle, round_point, in_handle) = subpaths[i].round_line_join(&subpaths[j], subpath.manipulator_groups()[j].anchor);
+					let last_index = subpaths[i].manipulator_groups().len() - 1;
+					subpaths[i].manipulator_groups_mut()[last_index].out_handle = Some(out_handle);
+					subpaths[i].manipulator_groups_mut().push(round_point);
+					subpaths[j].manipulator_groups_mut()[0].in_handle = Some(in_handle);
+				}
+			}
+		}
+	}
+
+	// Clip any overlap in the last segment
+	if subpath.closed {
+		let out_tangent = subpath.get_segment(subpath.len_segments() - 1).unwrap().tangent(TValue::Parametric(1.));
+		let in_tangent = subpath.get_segment(0).unwrap().tangent(TValue::Parametric(0.));
+		let angle = out_tangent.angle_to(in_tangent);
+
+		let mut apply_join = true;
+		if (angle > 0. && distance > 0.) || (angle < 0. && distance < 0.) {
+			if let Some((clipped_subpath1, clipped_subpath2)) = Subpath::clip_simple_subpaths(&subpaths[subpaths.len() - 1], &subpaths[0]) {
+				// Merge the clipped subpaths
+				let last_index = subpaths.len() - 1;
+				subpaths[last_index] = clipped_subpath1;
+				subpaths[0] = clipped_subpath2;
+				apply_join = false;
+			}
+		}
+		if apply_join {
+			drop_common_point[0] = false;
+			match join {
+				Join::Bevel => {}
+				Join::Miter(miter_limit) => {
+					let last_subpath_index = subpaths.len() - 1;
+					let miter_manipulator_group = subpaths[last_subpath_index].miter_line_join(&subpaths[0], miter_limit);
+					if let Some(miter_manipulator_group) = miter_manipulator_group {
+						subpaths[last_subpath_index].manipulator_groups_mut().push(miter_manipulator_group);
+					}
+				}
+				Join::Round => {
+					let last_subpath_index = subpaths.len() - 1;
+					let (out_handle, round_point, in_handle) = subpaths[last_subpath_index].round_line_join(&subpaths[0], subpath.manipulator_groups()[0].anchor);
+					let last_index = subpaths[last_subpath_index].manipulator_groups().len() - 1;
+					subpaths[last_subpath_index].manipulator_groups_mut()[last_index].out_handle = Some(out_handle);
+					subpaths[last_subpath_index].manipulator_groups_mut().push(round_point);
+					subpaths[0].manipulator_groups_mut()[0].in_handle = Some(in_handle);
+				}
+			}
+		}
+	}
+
+	// Merge the subpaths. Drop points which overlap with one another.
+	let mut manipulator_groups = subpaths[0].manipulator_groups().to_vec();
+	for i in 1..subpaths.len() {
+		if drop_common_point[i] {
+			let last_group = manipulator_groups.pop().unwrap();
+			let mut manipulators_copy = subpaths[i].manipulator_groups().to_vec();
+			manipulators_copy[0].in_handle = last_group.in_handle;
+
+			manipulator_groups.append(&mut manipulators_copy);
+		} else {
+			manipulator_groups.append(&mut subpaths[i].manipulator_groups().to_vec());
+		}
+	}
+	if subpath.closed && drop_common_point[0] {
+		let last_group = manipulator_groups.pop().unwrap();
+		manipulator_groups[0].in_handle = last_group.in_handle;
+	}
+
+	Subpath::new(manipulator_groups, subpath.closed)
+}

node-graph/gcore/src/vector/vector_nodes.rs

@@ -1,3 +1,4 @@
+use super::algorithms::offset_subpath::offset_subpath;
 use super::misc::CentroidType;
 use super::style::{Fill, Gradient, GradientStops, Stroke};
 use super::{PointId, SegmentDomain, SegmentId, StrokeId, VectorData, VectorDataTable};
@@ -993,7 +994,8 @@ async fn offset_path(_: impl Ctx, vector_data: VectorDataTable, distance: f64, l
 		subpath.apply_transform(vector_data_transform);
 
 		// Taking the existing stroke data and passing it to Bezier-rs to generate new paths.
-		let mut subpath_out = subpath.offset(
+		let mut subpath_out = offset_subpath(
+			&subpath,
 			-distance,
 			match line_join {
 				LineJoin::Miter => Join::Miter(Some(miter_limit)),