Assimp FBX Import support

Issues fixed:
- Updated assimp to latest and backported fixes into godot.
- Fixed file scale being ignored from FBX file.
- Fixed bone removal
- Implemented proper armature binding
- Fixed recursion not always going through the entire path
- Implemented assimp global scaling system
- Fixed assimp global scale process to support unit conversion
- Implemented proper fbx scaling
- Fixed asserts caused by missing faces in some models which could crash
- Fixed valid bone removal
- Fixed root node being overwriten by assimp which caused data loss
- Fixed armature construction so that it works with multiple roots
- Implemented basic support for FBX standard materials
- Refactoring to improve code quality and improve function reuse.
- Simplified node creation from assimp scene into subsections: create_light, create_mesh, create_bone.
- Creating meshes is now done after hierarchy is created so that the skeleton is always available.
- Added support to assimp to support file scale in all formats which call SetFileScale.
- Many other fixes provided into assimp.

Known issues:
- FBX pivots from Maya do not currently work. (workaround: for now use blender import and export to remove pivot tracks)
- Hierarchy creates an extra node for each mesh - this was done intentionally but we intended to do a pass to remove these as they're a required node.
- When an animated mesh has not executed any animation the rest pose is wrong.

Co-authored-by: K. S. Ernest (iFire) Lee <ernest.lee@chibifire.com>

thirdparty/assimp/code/PostProcessing/ScaleProcess.cpp

@@ -39,19 +39,17 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 ----------------------------------------------------------------------
 */
-#ifndef ASSIMP_BUILD_NO_GLOBALSCALE_PROCESS
-
 #include "ScaleProcess.h"
 
 #include <assimp/scene.h>
 #include <assimp/postprocess.h>
+#include <assimp/BaseImporter.h>
 
 namespace Assimp {
 
 ScaleProcess::ScaleProcess()
 : BaseProcess()
 , mScale( AI_CONFIG_GLOBAL_SCALE_FACTOR_DEFAULT ) {
-    // empty
 }
 
 ScaleProcess::~ScaleProcess() {
@@ -71,10 +69,26 @@ bool ScaleProcess::IsActive( unsigned int pFlags ) const {
 }
 
 void ScaleProcess::SetupProperties( const Importer* pImp ) {
-    mScale = pImp->GetPropertyFloat( AI_CONFIG_GLOBAL_SCALE_FACTOR_KEY, 0 );
+    // User scaling
+    mScale = pImp->GetPropertyFloat( AI_CONFIG_GLOBAL_SCALE_FACTOR_KEY, 1.0f );
+
+    // File scaling * Application Scaling
+    float importerScale = pImp->GetPropertyFloat( AI_CONFIG_APP_SCALE_KEY, 1.0f );
+
+    // apply scale to the scale 
+    // helps prevent bugs with backward compatibility for anyone using normal scaling.
+    mScale *= importerScale;
 }
 
 void ScaleProcess::Execute( aiScene* pScene ) {
+    if(mScale == 1.0f)  {
+        return; // nothing to scale
+    }
+    
+    ai_assert( mScale != 0 );
+    ai_assert( nullptr != pScene );
+    ai_assert( nullptr != pScene->mRootNode );
+
     if ( nullptr == pScene ) {
         return;
     }
@@ -82,22 +96,113 @@ void ScaleProcess::Execute( aiScene* pScene ) {
     if ( nullptr == pScene->mRootNode ) {
         return;
     }
+    
+    // Process animations and update position transform to new unit system
+    for( unsigned int animationID = 0; animationID < pScene->mNumAnimations; animationID++ )
+    {
+        aiAnimation* animation = pScene->mAnimations[animationID];
+
+        for( unsigned int animationChannel = 0; animationChannel < animation->mNumChannels; animationChannel++)
+        {
+            aiNodeAnim* anim = animation->mChannels[animationChannel];
+            
+            for( unsigned int posKey = 0; posKey < anim->mNumPositionKeys; posKey++)
+            {
+                aiVectorKey& vectorKey = anim->mPositionKeys[posKey];
+                vectorKey.mValue *= mScale;
+            }
+        }
+    }
+
+    for( unsigned int meshID = 0; meshID < pScene->mNumMeshes; meshID++)
+    {
+        aiMesh *mesh = pScene->mMeshes[meshID]; 
+        
+        // Reconstruct mesh vertexes to the new unit system
+        for( unsigned int vertexID = 0; vertexID < mesh->mNumVertices; vertexID++)
+        {
+            aiVector3D& vertex = mesh->mVertices[vertexID];
+            vertex *= mScale;
+        }
+
+
+        // bone placement / scaling
+        for( unsigned int boneID = 0; boneID < mesh->mNumBones; boneID++)
+        {
+            // Reconstruct matrix by transform rather than by scale 
+            // This prevent scale values being changed which can
+            // be meaningful in some cases 
+            // like when you want the modeller to see 1:1 compatibility.
+            aiBone* bone = mesh->mBones[boneID];
+
+            aiVector3D pos, scale;
+            aiQuaternion rotation;
+
+            bone->mOffsetMatrix.Decompose( scale, rotation, pos);
+            
+            aiMatrix4x4 translation;
+            aiMatrix4x4::Translation( pos * mScale, translation );
+            
+            aiMatrix4x4 scaling;
+            aiMatrix4x4::Scaling( aiVector3D(scale), scaling );
+
+            aiMatrix4x4 RotMatrix = aiMatrix4x4 (rotation.GetMatrix());
+
+            bone->mOffsetMatrix = translation * RotMatrix * scaling;
+        }
+
+
+        // animation mesh processing
+        // convert by position rather than scale.
+        for( unsigned int animMeshID = 0; animMeshID < mesh->mNumAnimMeshes; animMeshID++)
+        {
+            aiAnimMesh * animMesh = mesh->mAnimMeshes[animMeshID];
+            
+            for( unsigned int vertexID = 0; vertexID < animMesh->mNumVertices; vertexID++)
+            {
+                aiVector3D& vertex = animMesh->mVertices[vertexID];
+                vertex *= mScale;
+            }
+        }
+    }
 
     traverseNodes( pScene->mRootNode );
 }
 
-void ScaleProcess::traverseNodes( aiNode *node ) {
+void ScaleProcess::traverseNodes( aiNode *node, unsigned int nested_node_id ) {    
     applyScaling( node );
+
+    for( size_t i = 0; i < node->mNumChildren; i++)
+    {
+        // recurse into the tree until we are done!
+        traverseNodes( node->mChildren[i], nested_node_id+1 ); 
+    }
 }
 
 void ScaleProcess::applyScaling( aiNode *currentNode ) {
     if ( nullptr != currentNode ) {
-        currentNode->mTransformation.a1 = currentNode->mTransformation.a1 * mScale;
-        currentNode->mTransformation.b2 = currentNode->mTransformation.b2 * mScale;
-        currentNode->mTransformation.c3 = currentNode->mTransformation.c3 * mScale;
+        // Reconstruct matrix by transform rather than by scale 
+        // This prevent scale values being changed which can
+        // be meaningful in some cases 
+        // like when you want the modeller to 
+        // see 1:1 compatibility.
+        
+        aiVector3D pos, scale;
+        aiQuaternion rotation;
+        currentNode->mTransformation.Decompose( scale, rotation, pos);
+        
+        aiMatrix4x4 translation;
+        aiMatrix4x4::Translation( pos * mScale, translation );
+        
+        aiMatrix4x4 scaling;
+
+        // note: we do not use mScale here, this is on purpose.
+        aiMatrix4x4::Scaling( scale, scaling );
+
+        aiMatrix4x4 RotMatrix = aiMatrix4x4 (rotation.GetMatrix());
+
+        currentNode->mTransformation = translation * RotMatrix * scaling;
     }
 }
 
 } // Namespace Assimp
-
-#endif // !! ASSIMP_BUILD_NO_GLOBALSCALE_PROCESS