Merge pull request donkeyProgramming#203 from mr-phazer/Fix-ReculateT…

…angentBasis-OnImport

Calculations of TangentBasis for imported GLTF models

Editors/ImportExportEditor/Editors.ImportExport/Importing/Importers/GltfToRmv/Helper/RmvMeshBuilder.cs

@@ -123,6 +123,9 @@ private static RmvMesh GenerateRmvMesh(SharpGLTF.Schema2.Mesh mesh)
                 rmv2Mesh.IndexList[i + 1] = (ushort)indices[i + 2];
             }            
 
+            // recæculate tangents and bitangents
+            TangentBasisCalculator.CalculateForRmv2Mesh(rmv2Mesh);
+
             return rmv2Mesh;
         }
 

Editors/ImportExportEditor/Editors.ImportExport/Importing/Importers/GltfToRmv/Helper/TangentBasisCalculator.cs

@@ -0,0 +1,67 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.Xna.Framework;
+using Shared.GameFormats.RigidModel;
+
+namespace Editors.ImportExport.Importing.Importers.GltfToRmv.Helper
+{
+    public class TangentBasisCalculator
+    {
+        public static void CalculateForRmv2Mesh(RmvMesh rmv2Mesh)
+        {
+            for (var i = 0; i < rmv2Mesh.IndexList.Length; i += 3)
+            {
+                var i0 = rmv2Mesh.IndexList[i];
+                var i1 = rmv2Mesh.IndexList[i + 1];
+                var i2 = rmv2Mesh.IndexList[i + 2];
+
+                var v0 = rmv2Mesh.VertexList[i0];
+                var v1 = rmv2Mesh.VertexList[i1];
+                var v2 = rmv2Mesh.VertexList[i2];
+
+                // Calculate the edges of the triangle
+                var edge1 = v1.Position - v0.Position;
+                var edge2 = v2.Position - v0.Position;
+
+                // Calculate the differences in UV coordinates
+                var deltaUV1 = v1.Uv - v0.Uv;
+                var deltaUV2 = v2.Uv - v0.Uv;
+
+                // Calculate the tangent and bitangent
+                float f = 1.0f / (deltaUV1.X * deltaUV2.Y - deltaUV2.X * deltaUV1.Y);
+
+                var tangent = new Vector3(
+                    f * (deltaUV2.Y * edge1.X - deltaUV1.Y * edge2.X),
+                    f * (deltaUV2.Y * edge1.Y - deltaUV1.Y * edge2.Y),
+                    f * (deltaUV2.Y * edge1.Z - deltaUV1.Y * edge2.Z)
+                );               
+
+                var bitangent = new Vector3(
+                    f * (-deltaUV2.X * edge1.X + deltaUV1.X * edge2.X),
+                    f * (-deltaUV2.X * edge1.Y + deltaUV1.X * edge2.Y),
+                    f * (-deltaUV2.X * edge1.Z + deltaUV1.X * edge2.Z)
+                );
+
+                // Add to existing vectors, has the effect of a "weighted average"
+                v0.Tangent += tangent;
+                v1.Tangent += tangent;
+                v2.Tangent += tangent;
+
+                v0.BiNormal += bitangent;
+                v1.BiNormal += bitangent;
+                v2.BiNormal += bitangent;
+            }
+
+            // normalize the "averaged" vectors
+            foreach (var vertex in rmv2Mesh.VertexList)
+            { 
+               // TODO: orthogonalize the tangents and bitangents?
+                vertex.Tangent = Vector3.Normalize(vertex.Tangent);
+                vertex.BiNormal = Vector3.Normalize(vertex.BiNormal);
+            }
+        }
+    }
+}