Initial work on rollback and refactor

src/stage/line.rs

@@ -0,0 +1,34 @@
+//! Stage collision geometry.
+
+use bevy::{math::InvalidDirectionError, prelude::*};
+
+use crate::math::SegmentIntersection;
+
+#[derive(Component, Reflect, Clone, Default)]
+#[reflect(Component)]
+pub struct StageLine {
+    pub segment: Segment2d,
+    pub normal: Vec2,
+}
+
+pub struct StagePlaneIntersectResult {
+    pub position: Vec2,
+}
+
+impl StageLine {
+    pub fn new(start: Vec2, end: Vec2) -> Result<Self, InvalidDirectionError> {
+        let segment = Segment2d::new(start, end);
+        let normal = segment.left_normal().as_vec2();
+        Ok(Self { segment, normal })
+    }
+
+    pub fn intersect_ray(&self, segment: Segment2d) -> Option<StagePlaneIntersectResult> {
+        self.segment
+            .segment_intersection(&segment)
+            .map(|position| StagePlaneIntersectResult { position })
+    }
+
+    pub fn project(&self, vec: Vec2) -> Vec2 {
+        vec - vec.project_onto_normalized(self.normal)
+    }
+}