Freehand tool: Allow extension of existing paths (#1594)

* feat: extend freehand path

* fix: rm logs

* fix: rename variable

editor/src/messages/tool/common_functionality/mod.rs

@@ -5,3 +5,4 @@ pub mod resize;
 pub mod shape_editor;
 pub mod snapping;
 pub mod transformation_cage;
+pub mod utility_funcitons;

editor/src/messages/tool/common_functionality/utility_funcitons.rs

@@ -0,0 +1,34 @@
+use crate::messages::portfolio::document::utility_types::document_metadata::LayerNodeIdentifier;
+use crate::messages::prelude::*;
+use crate::messages::tool::common_functionality::graph_modification_utils::get_subpaths;
+use glam::DVec2;
+
+/// Determines if a path should be extended. Returns the path and if it is extending from the start, if applicable.
+pub fn should_extend(document: &DocumentMessageHandler, pos: DVec2, tolerance: f64) -> Option<(LayerNodeIdentifier, usize, bool)> {
+	let mut best = None;
+	let mut best_distance_squared = tolerance * tolerance;
+
+	for layer in document.selected_nodes.selected_layers(document.metadata()) {
+		let viewspace = document.metadata().transform_to_viewport(layer);
+
+		let subpaths = get_subpaths(layer, &document.network)?;
+		for (subpath_index, subpath) in subpaths.iter().enumerate() {
+			if subpath.closed() {
+				continue;
+			}
+
+			for (manipulator_group, from_start) in [(subpath.manipulator_groups().first(), true), (subpath.manipulator_groups().last(), false)] {
+				let Some(manipulator_group) = manipulator_group else { break };
+
+				let distance_squared = viewspace.transform_point2(manipulator_group.anchor).distance_squared(pos);
+
+				if distance_squared < best_distance_squared {
+					best = Some((layer, subpath_index, from_start));
+					best_distance_squared = distance_squared;
+				}
+			}
+		}
+	}
+
+	best
+}