LineMaterial: Fix clipping at edge artifacts (#27349)

* Fix containing cube

* Sceenshot update

Author: gkjohnson

examples/jsm/lines/LineMaterial.js

@@ -169,51 +169,34 @@ ShaderLib[ 'line' ] = {
 
 			#ifdef WORLD_UNITS
 
-				// get the offset direction as perpendicular to the view vector
 				vec3 worldDir = normalize( end.xyz - start.xyz );
-				vec3 offset;
-				if ( position.y < 0.5 ) {
+				vec3 tmpFwd = normalize( mix( start.xyz, end.xyz, 0.5 ) );
+				vec3 worldUp = normalize( cross( worldDir, tmpFwd ) );
+				vec3 worldFwd = cross( worldDir, worldUp );
+				worldPos = position.y < 0.5 ? start: end;
 
-					offset = normalize( cross( start.xyz, worldDir ) );
-
-				} else {
-
-					offset = normalize( cross( end.xyz, worldDir ) );
-
-				}
-
-				// sign flip
-				if ( position.x < 0.0 ) offset *= - 1.0;
-
-				float forwardOffset = dot( worldDir, vec3( 0.0, 0.0, 1.0 ) );
+				// height offset
+				float hw = linewidth * 0.5;
+				worldPos.xyz += position.x < 0.0 ? hw * worldUp : - hw * worldUp;
 
 				// don't extend the line if we're rendering dashes because we
 				// won't be rendering the endcaps
 				#ifndef USE_DASH
 
-					// extend the line bounds to encompass  endcaps
-					start.xyz += - worldDir * linewidth * 0.5;
-					end.xyz += worldDir * linewidth * 0.5;
+					// cap extension
+					worldPos.xyz += position.y < 0.5 ? - hw * worldDir : hw * worldDir;
 
-					// shift the position of the quad so it hugs the forward edge of the line
-					offset.xy -= dir * forwardOffset;
-					offset.z += 0.5;
+					// add width to the box
+					worldPos.xyz += worldFwd * hw;
 
-				#endif
-
-				// endcaps
-				if ( position.y > 1.0 || position.y < 0.0 ) {
-
-					offset.xy += dir * 2.0 * forwardOffset;
+					// endcaps
+					if ( position.y > 1.0 || position.y < 0.0 ) {
 
-				}
+						worldPos.xyz -= worldFwd * 2.0 * hw;
 
-				// adjust for linewidth
-				offset *= linewidth * 0.5;
+					}
 
-				// set the world position
-				worldPos = ( position.y < 0.5 ) ? start : end;
-				worldPos.xyz += offset;
+				#endif
 
 				// project the worldpos
 				vec4 clip = projectionMatrix * worldPos;