Revert some changes

Author: gkjohnson

src/utils/trimToBeneathTriPlane.js

@@ -1,4 +1,4 @@
-import { Plane, Vector3, MathUtils, PlaneHelper } from 'three';
+import { Plane, Vector3 } from 'three';
 import { isYProjectedTriangleDegenerate } from './triangleLineUtils.js';
 
 const EPSILON = 1e-16;
@@ -35,8 +35,7 @@ export function trimToBeneathTriPlane( tri, line, lineTarget ) {
 	line.delta( _lineDirection ).normalize();
 	if ( Math.abs( _plane.normal.dot( _lineDirection ) ) < EPSILON ) {
 
-		// if the line is definitely above or on the plane then skip it
-		if ( ( isStartOnPlane || ! isStartBelow ) && ( isEndOnPlane || ! isEndBelow ) ) {
+		if ( isStartOnPlane || ! isStartBelow ) {
 
 			return false;
 
@@ -64,20 +63,40 @@ export function trimToBeneathTriPlane( tri, line, lineTarget ) {
 
 	} else {
 
-		const t = MathUtils.mapLinear( 0, startDist, endDist, 0, 1 );
-		line.at( t, _planeHit );
+		let didHit = _plane.intersectLine( line, _planeHit );
+		if ( ! didHit ) {
 
-		if ( isStartBelow ) {
+			if ( isStartOnPlane ) {
 
-			lineTarget.start.copy( line.start );
-			lineTarget.end.copy( _planeHit );
-			return true;
+				_planeHit.copy( line.start );
+				didHit = true;
 
-		} else if ( isEndBelow ) {
+			}
 
-			lineTarget.end.copy( line.end );
-			lineTarget.start.copy( _planeHit );
-			return true;
+			if ( isEndOnPlane ) {
+
+				_planeHit.copy( line.end );
+				didHit = true;
+
+			}
+
+		}
+
+		if ( didHit ) {
+
+			if ( isStartBelow ) {
+
+				lineTarget.start.copy( line.start );
+				lineTarget.end.copy( _planeHit );
+				return true;
+
+			} else if ( isEndBelow ) {
+
+				lineTarget.end.copy( line.end );
+				lineTarget.start.copy( _planeHit );
+				return true;
+
+			}
 
 		}