From 41c219697d180f38a960fa791e0840b9c9953502 Mon Sep 17 00:00:00 2001
From: Will Jessup <will@willjessup.com>
Date: Sun, 28 Jul 2019 10:22:27 -0700
Subject: [PATCH] added vertexColors to slicing function

I followed the code structure and added in the vertexColors to the Face3 that come from Geometry.colors. This is used when color is applied by the shader to each vertex and not by the material.
---
 src/slice.js | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/slice.js b/src/slice.js
index a5228ff..045589a 100644
--- a/src/slice.js
+++ b/src/slice.js
@@ -48,22 +48,23 @@ module.exports = function(THREE) {
                 var index = face[key];
                 var distance = distances[index];
                 var position = positions[index];
+                var color = geometry.colors[index];
                 
                 if (position === FRONT) {
                     if (lastPosition === BACK) {
-                        builder.addIntersection(lastKey, key, lastDistance, distance);
-                        builder.addVertex(key);
+                        builder.addIntersection(lastKey, key, color, lastDistance, distance);
+                        builder.addVertex(key, color);
                     } else {
-                        builder.addVertex(key);
+                        builder.addVertex(key, color);
                     }
                 }
 
                 if (position === ON) {
-                    builder.addVertex(key);
+                    builder.addVertex(key, color);
                 }
 
                 if (position === BACK && lastPosition === FRONT) {
-                    builder.addIntersection(lastKey, key, lastDistance, distance);
+                    builder.addIntersection(lastKey, key, color, lastDistance, distance);
                 }
 
                 lastKey = key;
@@ -113,6 +114,7 @@ module.exports = function(THREE) {
         this.faceIndices = [];
         this.faceNormals = [];
         this.faceUvs = [];
+        this.colors = [];
     };
 
     GeometryBuilder.prototype.endFace = function() {
@@ -138,7 +140,7 @@ module.exports = function(THREE) {
             }, this);
     };
 
-    GeometryBuilder.prototype.addVertex = function(key) {
+    GeometryBuilder.prototype.addVertex = function(key, color) {
         this.addUv(key);
         this.addNormal(key);
 
@@ -154,9 +156,10 @@ module.exports = function(THREE) {
             this.addedVertices[index] = newIndex;
         }
         this.faceIndices.push(newIndex);
+        this.colors.push(color);
     };
 
-    GeometryBuilder.prototype.addIntersection = function(keyA, keyB, distanceA, distanceB) {
+    GeometryBuilder.prototype.addIntersection = function(keyA, keyB, color, distanceA, distanceB) {
         var t = Math.abs(distanceA) / (Math.abs(distanceA) + Math.abs(distanceB));
         this.addIntersectionUv(keyA, keyB, t);
         this.addIntersectionNormal(keyA, keyB, t);
@@ -177,6 +180,7 @@ module.exports = function(THREE) {
             this.addedIntersections[id] = index;
         }
         this.faceIndices.push(index);
+        this.colors.push(color);
         this.updateNewEdges(index);
     };
 
@@ -270,6 +274,11 @@ module.exports = function(THREE) {
             this.faceIndices[c],
             normals
         );
+        
+        face.vertexColors[0] = this.colors[a];
+        face.vertexColors[1] = this.colors[b];
+        face.vertexColors[2] = this.colors[c];
+        
         this.targetGeometry.faces.push(face);
         if ( ! this.sourceFaceUvs) {
             return;