Add support for up to 4 texcoords

Also, don't warn about texcoord2 coming in from Tilt Brush glTF.
More recent versions of Tilt Brush allow putting stroke timestamp
data into texcoord2.

Change-Id: Id000b0151176f0e4ab2a0cca17eb37ba24f6604c

UnitySDK/Assets/TiltBrush/Scripts/BrushDescriptor.cs

@@ -28,6 +28,7 @@ public enum Semantic {
     XyIsUvZIsDistance,
     UnitlessVector,
     XyIsUv,
+    Timestamp,
   }
 
   public Material Material { get { return m_Material; } }

UnitySDK/Assets/TiltBrush/Scripts/Gltf/GltfSchemaCommon.cs

@@ -134,7 +134,7 @@ public class MeshPrecursor {
   public Vector3[] normals;
   public Color[] colors;
   public Vector4[] tangents;
-  public Array[] uvSets = new Array[2];
+  public Array[] uvSets = new Array[4];
   public int[] triangles;
 }
 

UnitySDK/Assets/TiltBrush/Scripts/Gltf/ImportGltf.cs

@@ -825,6 +825,7 @@ private static void StoreDataInMesh(
       ImportState state,
       BrushDescriptor desc, string semantic, Array data,
       MeshPrecursor mesh) {
+    int txcChannel;
     switch (semantic) {
     case "POSITION":
       ChangeBasisAndApplyScale(data, Semantic.Position, state.scaleFactor, state.unityFromGltf);
@@ -872,20 +873,24 @@ private static void StoreDataInMesh(
           data, Semantic.UnitlessVector, state.scaleFactor, state.unityFromGltf);
       mesh.tangents = (Vector4[]) data;
       break;
-    case "TEXCOORD_0": {
-      var ptSemantic = GetTexcoordSemantic(state, desc, 0);
+    case "TEXCOORD_0":
+      txcChannel = 0;
+      goto GenericTexcoord;
+    case "TEXCOORD_1":
+      txcChannel = 1;
+      goto GenericTexcoord;
+    case "TEXCOORD_2":
+      txcChannel = 2;
+      goto GenericTexcoord;
+    case "TEXCOORD_3":
+      txcChannel = 3;
+      goto GenericTexcoord;
+GenericTexcoord:
+      var ptSemantic = GetTexcoordSemantic(state, desc, txcChannel);
       ChangeBasisAndApplyScale(data, ptSemantic, state.scaleFactor, state.unityFromGltf);
       ChangeUvBasis(data, ptSemantic);
-      mesh.uvSets[0] = data;
+      mesh.uvSets[txcChannel] = data;
       break;
-    }
-    case "TEXCOORD_1": {
-      var ptSemantic = GetTexcoordSemantic(state, desc, 1);
-      ChangeBasisAndApplyScale(data, ptSemantic, state.scaleFactor, state.unityFromGltf);
-      ChangeUvBasis(data, ptSemantic);
-      mesh.uvSets[1] = data;
-      break;
-    }
     case "VERTEXID":
       // This was an attempt to get vertex id in webgl, but it didn't work out.
       // The data is not fully hooked-up in the gltf, and it doesn't make its way to THREE.
@@ -992,6 +997,9 @@ static Semantic GetTexcoordSemantic(ImportState state, BrushDescriptor desc, int
           return desc.m_uv0Semantic;
         } else if (uvChannel == 1) {
           return desc.m_uv1Semantic;
+        } else if (uvChannel == 2) {
+          // All brushes use texcoord2 as (optional) timestamp data
+          return Semantic.Timestamp;
         } else {
           Debug.LogWarningFormat("Unexpected TB texcoord: {0}", uvChannel);
           return Semantic.Unspecified;