#1126 gltf scene import prototype (#1172)

* #1126 GLTF Scene import initial prototype (working geometry import for some assets)

* #1126 WIP -- Expand support for more vertex formats, PoC material import, shadow support, scale support

* #1126 move GLTF implementation to newview/gltf

* #1126 Refactor attribute loading to be less copy/pasta for each combination of types

* #1126 Partially working object selection.  Ability to have multiple scenes at once.  Helpful message on how to use the preview button.

* #1126 Add bounding box debug display and untangle GLTF raycast from LLVOVolume raycast

* #1126 Working raycast on GLTF scenes.

* #1126 Remove some #pragma optimize offs

4 files changed, 1274 insertions, 0 deletions

diff --git a/indra/newview/gltf/asset.cpp b/indra/newview/gltf/asset.cpp
new file mode 100644
index 0000000000..18f814c5b6
--- /dev/null
+++ b/indra/newview/gltf/asset.cpp
@@ -0,0 +1,209 @@
+/**
+ * @file asset.cpp
+ * @brief LL GLTF Implementation
+ *
+ * $LicenseInfo:firstyear=2024&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2024, Linden Research, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#include "asset.h"
+#include "llvolumeoctree.h"
+
+using namespace LL::GLTF;
+
+void Scene::updateTransforms(Asset& asset)
+{
+    LLMatrix4a identity;
+    identity.setIdentity();
+    for (auto& nodeIndex : mNodes)
+    {
+        Node& node = asset.mNodes[nodeIndex];
+        node.updateTransforms(asset, identity);
+    }
+}
+
+void Scene::updateRenderTransforms(Asset& asset, const LLMatrix4a& modelview)
+{
+    for (auto& nodeIndex : mNodes)
+    {
+        Node& node = asset.mNodes[nodeIndex];
+        node.updateRenderTransforms(asset, modelview);
+    }
+}
+
+void Node::updateRenderTransforms(Asset& asset, const LLMatrix4a& modelview)
+{
+    matMul(mMatrix, modelview, mRenderMatrix);
+
+    for (auto& childIndex : mChildren)
+    {
+        Node& child = asset.mNodes[childIndex];
+        child.updateRenderTransforms(asset, mRenderMatrix);
+    }
+}
+
+LLMatrix4a inverse(const LLMatrix4a& mat);
+
+void Node::updateTransforms(Asset& asset, const LLMatrix4a& parentMatrix)
+{
+    matMul(mMatrix, parentMatrix, mAssetMatrix);
+    mAssetMatrixInv = inverse(mAssetMatrix);
+    
+    for (auto& childIndex : mChildren)
+    {
+        Node& child = asset.mNodes[childIndex];
+        child.updateTransforms(asset, mAssetMatrix);
+    }
+}
+
+void Asset::updateTransforms()
+{
+    for (auto& scene : mScenes)
+    {
+        scene.updateTransforms(*this);
+    }
+}
+
+void Asset::updateRenderTransforms(const LLMatrix4a& modelview)
+{
+#if 0
+    // traverse hierarchy and update render transforms from scratch
+    for (auto& scene : mScenes)
+    {
+        scene.updateRenderTransforms(*this, modelview);
+    }
+#else
+    // use mAssetMatrix to update render transforms from node list
+    for (auto& node : mNodes)
+    {
+        if (node.mMesh != INVALID_INDEX)
+        {
+            matMul(node.mAssetMatrix, modelview, node.mRenderMatrix);
+        }
+    }
+
+#endif
+
+}
+
+S32 Asset::lineSegmentIntersect(const LLVector4a& start, const LLVector4a& end,
+    LLVector4a* intersection,         // return the intersection point
+    LLVector2* tex_coord,            // return the texture coordinates of the intersection point
+    LLVector4a* normal,               // return the surface normal at the intersection point
+    LLVector4a* tangent,             // return the surface tangent at the intersection point
+    S32* primitive_hitp
+)
+{
+    S32 node_hit = -1;
+    S32 primitive_hit = -1;
+
+    LLVector4a local_start;
+    LLVector4a asset_end = end;
+    LLVector4a local_end;
+    LLVector4a p;
+
+
+    for (auto& node : mNodes)
+    {
+        if (node.mMesh != INVALID_INDEX)
+        {
+            
+            bool newHit = false;
+
+            // transform start and end to this node's local space
+            node.mAssetMatrixInv.affineTransform(start, local_start);
+            node.mAssetMatrixInv.affineTransform(asset_end, local_end);
+
+            Mesh& mesh = mMeshes[node.mMesh];
+            for (auto& primitive : mesh.mPrimitives)
+            {
+                const LLVolumeTriangle* tri = primitive.lineSegmentIntersect(local_start, local_end, &p, tex_coord, normal, tangent);
+                if (tri)
+                {
+                    newHit = true;
+                    local_end = p;
+
+                    // pointer math to get the node index
+                    node_hit = &node - &mNodes[0];
+                    llassert(&mNodes[node_hit] == &node);
+
+                    //pointer math to get the primitive index
+                    primitive_hit = &primitive - &mesh.mPrimitives[0];
+                    llassert(&mesh.mPrimitives[primitive_hit] == &primitive);
+                }
+            }
+
+            if (newHit)
+            {
+                // shorten line segment on hit
+                node.mAssetMatrix.affineTransform(p, asset_end); 
+
+                // transform results back to asset space
+                if (intersection)
+                {
+                    *intersection = asset_end;
+                }
+
+                if (normal || tangent)
+                {
+                    LLMatrix4 normalMatrix(node.mAssetMatrixInv.getF32ptr());
+
+                    normalMatrix.transpose();
+
+                    LLMatrix4a norm_mat;
+                    norm_mat.loadu((F32*)normalMatrix.mMatrix);
+
+                    if (normal)
+                    {
+                        LLVector4a n = *normal;
+                        F32 w = n.getF32ptr()[3];
+                        n.getF32ptr()[3] = 0.0f;
+
+                        norm_mat.affineTransform(n, *normal);
+                        normal->getF32ptr()[3] = w;
+                    }
+
+                    if (tangent)
+                    {
+                        LLVector4a t = *tangent;
+                        F32 w = t.getF32ptr()[3];
+                        t.getF32ptr()[3] = 0.0f;
+
+                        norm_mat.affineTransform(t, *tangent);
+                        tangent->getF32ptr()[3] = w;
+                    }
+                }
+            }
+        }
+    }
+
+    if (node_hit != -1)
+    {
+        if (primitive_hitp)
+        {
+            *primitive_hitp = primitive_hit;
+        }
+    }
+
+    return node_hit;
+}
+
+
diff --git a/indra/newview/gltf/asset.h b/indra/newview/gltf/asset.h
new file mode 100644
index 0000000000..0f1d4e8993
--- /dev/null
+++ b/indra/newview/gltf/asset.h
@@ -0,0 +1,445 @@
+#pragma once
+
+/**
+ * @file asset.h
+ * @brief LL GLTF Implementation
+ *
+ * $LicenseInfo:firstyear=2024&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2024, Linden Research, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#include "llvertexbuffer.h"
+#include "llvolumeoctree.h"
+#include "../lltinygltfhelper.h"
+#include "primitive.h"
+
+// LL GLTF Implementation
+namespace LL
+{
+    namespace GLTF
+    {
+        constexpr S32 INVALID_INDEX = -1;
+
+        class Asset;
+
+        class Buffer
+        {
+        public:
+            std::vector<U8> mData;
+            std::string mName;
+            std::string mUri;
+
+            const Buffer& operator=(const tinygltf::Buffer& src)
+            {
+                mData = src.data;
+                mName = src.name;
+                mUri = src.uri;
+                return *this;
+            }
+        };
+
+        class BufferView
+        {
+        public:
+            S32 mBuffer = INVALID_INDEX;
+            S32 mByteLength;
+            S32 mByteOffset;
+            S32 mByteStride;
+            S32 mTarget;
+            S32 mComponentType;
+
+            std::string mName;
+
+            const BufferView& operator=(const tinygltf::BufferView& src)
+            {
+                mBuffer = src.buffer;
+                mByteLength = src.byteLength;
+                mByteOffset = src.byteOffset;
+                mByteStride = src.byteStride;
+                mTarget = src.target;
+                mName = src.name;
+                return *this;
+            }
+        };
+
+        class Accessor
+        {
+        public:
+            S32 mBufferView = INVALID_INDEX;
+            S32 mByteOffset;
+            S32 mComponentType;
+            S32 mCount;
+            std::vector<double> mMax;
+            std::vector<double> mMin;
+            S32 mType;
+            bool mNormalized;
+            std::string mName;
+
+            const Accessor& operator=(const tinygltf::Accessor& src)
+            {
+                mBufferView = src.bufferView;
+                mByteOffset = src.byteOffset;
+                mComponentType = src.componentType;
+                mCount = src.count;
+                mType = src.type;
+                mNormalized = src.normalized;
+                mName = src.name;
+                mMax = src.maxValues;
+                mMin = src.maxValues;
+
+                return *this;
+            }
+        };
+
+        class Material
+        {
+        public:
+            // use LLFetchedGLTFMaterial for now, but eventually we'll want to use
+            // a more flexible GLTF material implementation instead of the fixed packing
+            // version we use for sharable GLTF material assets
+            LLPointer<LLFetchedGLTFMaterial> mMaterial;
+            std::string mName;
+
+            const Material& operator=(const tinygltf::Material& src)
+            {
+                mName = src.name;
+                return *this;
+            }
+
+            void allocateGLResources(Asset& asset)
+            {
+                // allocate material
+                mMaterial = new LLFetchedGLTFMaterial();
+            }
+        };
+
+        class Mesh
+        {
+        public:
+            std::vector<Primitive> mPrimitives;
+            std::vector<double> mWeights;
+            std::string mName;
+
+            const Mesh& operator=(const tinygltf::Mesh& src)
+            {
+                mPrimitives.resize(src.primitives.size());
+                for (U32 i = 0; i < src.primitives.size(); ++i)
+                {
+                    mPrimitives[i] = src.primitives[i];
+                }
+
+                mWeights = src.weights;
+                mName = src.name;
+
+                return *this;
+            }
+
+            void allocateGLResources(Asset& asset)
+            {
+                for (auto& primitive : mPrimitives)
+                {
+                    primitive.allocateGLResources(asset);
+                }
+            }
+
+        };
+
+        class Node
+        {
+        public:
+            LLMatrix4a mMatrix; //local transform
+            LLMatrix4a mRenderMatrix; //transform for rendering
+            LLMatrix4a mAssetMatrix; //transform from local to asset space
+            LLMatrix4a mAssetMatrixInv; //transform from asset to local space
+
+            std::vector<S32> mChildren;
+            S32 mMesh = INVALID_INDEX;
+            std::string mName;
+
+            const Node& operator=(const tinygltf::Node& src)
+            {
+                F32* dstMatrix = mMatrix.getF32ptr();
+
+                if (src.matrix.size() != 16)
+                {
+                    mMatrix.setIdentity();
+                }
+                else
+                {
+                    for (U32 i = 0; i < 16; ++i)
+                    {
+                        dstMatrix[i] = (F32)src.matrix[i];
+                    }
+                }
+                
+                mChildren = src.children;
+                mMesh = src.mesh;
+                mName = src.name;
+
+                return *this;
+            }
+
+            // Set mRenderMatrix to a transform that can be used for the current render pass
+            // modelview -- parent's render matrix
+            void updateRenderTransforms(Asset& asset, const LLMatrix4a& modelview);
+
+            // update mAssetMatrix and mAssetMatrixInv
+            void updateTransforms(Asset& asset, const LLMatrix4a& parentMatrix);
+            
+        };
+
+        class Scene
+        {
+        public:
+            std::vector<S32> mNodes;
+            std::string mName;
+
+            const Scene& operator=(const tinygltf::Scene& src)
+            {
+                mNodes = src.nodes;
+                mName = src.name;
+
+                return *this;
+            }
+
+            void updateTransforms(Asset& asset);
+            void updateRenderTransforms(Asset& asset, const LLMatrix4a& modelview);
+            
+        };
+
+        class Texture
+        {
+        public:
+            S32 mSampler = INVALID_INDEX;
+            S32 mSource = INVALID_INDEX;
+            std::string mName;
+
+            const Texture& operator=(const tinygltf::Texture& src)
+            {
+                mSampler = src.sampler;
+                mSource = src.source;
+                mName = src.name;
+
+                return *this;
+            }
+        };
+
+        class Sampler
+        {
+        public:
+            S32 mMagFilter;
+            S32 mMinFilter;
+            S32 mWrapS;
+            S32 mWrapT;
+            std::string mName;
+
+            const Sampler& operator=(const tinygltf::Sampler& src)
+            {
+                mMagFilter = src.magFilter;
+                mMinFilter = src.minFilter;
+                mWrapS = src.wrapS;
+                mWrapT = src.wrapT;
+                mName = src.name;
+
+                return *this;
+            }
+        };
+
+        class Image
+        {
+        public:
+            std::string mName;
+            std::string mUri;
+            std::string mMimeType;
+            std::vector<U8> mData;
+            S32 mWidth;
+            S32 mHeight;
+            S32 mComponent;
+            S32 mBits;
+            LLPointer<LLViewerFetchedTexture> mTexture;
+
+            const Image& operator=(const tinygltf::Image& src)
+            {
+                mName = src.name;
+                mUri = src.uri;
+                mMimeType = src.mimeType;
+                mData = src.image;
+                mWidth = src.width;
+                mHeight = src.height;
+                mComponent = src.component;
+                mBits = src.bits;
+
+                return *this;
+            }
+
+            void allocateGLResources()
+            {
+                // allocate texture
+
+            }
+        };
+
+        // C++ representation of a GLTF Asset
+        class Asset : public LLRefCount
+        {
+        public:
+            std::vector<Scene> mScenes;
+            std::vector<Node> mNodes;
+            std::vector<Mesh> mMeshes;
+            std::vector<Material> mMaterials;
+            std::vector<Buffer> mBuffers;
+            std::vector<BufferView> mBufferViews;
+            std::vector<Texture> mTextures;
+            std::vector<Sampler> mSamplers;
+            std::vector<Image> mImages;
+            std::vector<Accessor> mAccessors;
+
+            void allocateGLResources(const std::string& filename, const tinygltf::Model& model)
+            {
+                for (auto& mesh : mMeshes)
+                {
+                    mesh.allocateGLResources(*this);
+                }
+
+                for (auto& image : mImages)
+                {
+                    image.allocateGLResources();
+                }
+
+                for (U32 i = 0; i < mMaterials.size(); ++i)
+                {
+                    mMaterials[i].allocateGLResources(*this);
+                    LLTinyGLTFHelper::getMaterialFromModel(filename, model, i, mMaterials[i].mMaterial, mMaterials[i].mName, true);
+                }
+            }
+
+            // update asset-to-node and node-to-asset transforms
+            void updateTransforms();
+
+            // update node render transforms
+            void updateRenderTransforms(const LLMatrix4a& modelview);
+            
+            void renderOpaque()
+            {
+                for (auto& node : mNodes)
+                {
+                    if (node.mMesh != INVALID_INDEX)
+                    {
+                        Mesh& mesh = mMeshes[node.mMesh];
+                        for (auto& primitive : mesh.mPrimitives)
+                        {
+                            gGL.loadMatrix((F32*)node.mRenderMatrix.mMatrix);
+                            if (primitive.mMaterial != INVALID_INDEX)
+                            {
+                                Material& material = mMaterials[primitive.mMaterial];
+                                material.mMaterial->bind();
+                            }
+                            primitive.mVertexBuffer->setBuffer();
+                            if (primitive.mVertexBuffer->getNumIndices() > 0)
+                            {
+                                primitive.mVertexBuffer->draw(primitive.mGLMode, primitive.mVertexBuffer->getNumIndices(), 0);
+                            }
+                            else
+                            {
+                                primitive.mVertexBuffer->drawArrays(primitive.mGLMode, 0, primitive.mVertexBuffer->getNumVerts());
+                            }
+                        }
+                    }
+                }
+            }
+
+            // return the index of the node that the line segment intersects with, or -1 if no hit
+            // input and output values must be in this asset's local coordinate frame
+            S32 lineSegmentIntersect(const LLVector4a& start, const LLVector4a& end,
+                LLVector4a* intersection = nullptr,         // return the intersection point
+                LLVector2* tex_coord = nullptr,            // return the texture coordinates of the intersection point
+                LLVector4a* normal = nullptr,               // return the surface normal at the intersection point
+                LLVector4a* tangent = nullptr,             // return the surface tangent at the intersection point
+                S32* primitive_hitp = nullptr           // return the index of the primitive that was hit
+            );
+            
+            const Asset& operator=(const tinygltf::Model& src)
+            {
+                mScenes.resize(src.scenes.size());
+                for (U32 i = 0; i < src.scenes.size(); ++i)
+                {
+                    mScenes[i] = src.scenes[i];
+                }
+
+                mNodes.resize(src.nodes.size());
+                for (U32 i = 0; i < src.nodes.size(); ++i)
+                {
+                    mNodes[i] = src.nodes[i];
+                }
+
+                mMeshes.resize(src.meshes.size());
+                for (U32 i = 0; i < src.meshes.size(); ++i)
+                {
+                    mMeshes[i] = src.meshes[i];
+                }
+
+                mMaterials.resize(src.materials.size());
+                for (U32 i = 0; i < src.materials.size(); ++i)
+                {
+                    mMaterials[i] = src.materials[i];
+                }
+
+                mBuffers.resize(src.buffers.size());
+                for (U32 i = 0; i < src.buffers.size(); ++i)
+                {
+                    mBuffers[i] = src.buffers[i];
+                }
+
+                mBufferViews.resize(src.bufferViews.size());
+                for (U32 i = 0; i < src.bufferViews.size(); ++i)
+                {
+                    mBufferViews[i] = src.bufferViews[i];
+                }
+
+                mTextures.resize(src.textures.size());
+                for (U32 i = 0; i < src.textures.size(); ++i)
+                {
+                    mTextures[i] = src.textures[i];
+                }
+
+                mSamplers.resize(src.samplers.size());
+                for (U32 i = 0; i < src.samplers.size(); ++i)
+                {
+                    mSamplers[i] = src.samplers[i];
+                }
+
+                mImages.resize(src.images.size());
+                for (U32 i = 0; i < src.images.size(); ++i)
+                {
+                    mImages[i] = src.images[i];
+                }
+
+                mAccessors.resize(src.accessors.size());
+                for (U32 i = 0; i < src.accessors.size(); ++i)
+                {
+                    mAccessors[i] = src.accessors[i];
+                }
+
+                return *this;
+            }
+        };
+    }
+}
diff --git a/indra/newview/gltf/primitive.cpp b/indra/newview/gltf/primitive.cpp
new file mode 100644
index 0000000000..dca3ccf706
--- /dev/null
+++ b/indra/newview/gltf/primitive.cpp
@@ -0,0 +1,480 @@
+/**
+ * @file primitive.cpp
+ * @brief LL GLTF Implementation
+ *
+ * $LicenseInfo:firstyear=2024&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2024, Linden Research, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#include "asset.h"
+#include "../lltinygltfhelper.h"
+
+using namespace LL::GLTF;
+
+#ifndef __PRETTY_FUNCTION__
+#define __PRETTY_FUNCTION__ __FUNCSIG__
+#endif
+
+// copy one vec3 from src to dst
+template<class S, class T>
+void copyVec2(S* src, T& dst)
+{
+    LL_ERRS() << "TODO: implement " << __PRETTY_FUNCTION__ << LL_ENDL;
+}
+
+// copy one vec3 from src to dst
+template<class S, class T>
+void copyVec3(S* src, T& dst)
+{
+    LL_ERRS() << "TODO: implement " << __PRETTY_FUNCTION__ << LL_ENDL;
+}
+
+// copy one vec4 from src to dst
+template<class S, class T>
+void copyVec4(S* src, T& dst)
+{
+    LL_ERRS() << "TODO: implement " << __PRETTY_FUNCTION__ << LL_ENDL;
+}
+
+template<>
+void copyVec2<F32, LLVector2>(F32* src, LLVector2& dst)
+{
+    dst.set(src[0], src[1]);
+}
+
+template<>
+void copyVec3<F32, LLVector4a>(F32* src, LLVector4a& dst)
+{
+    dst.load3(src);
+}
+
+template<>
+void copyVec3<U16, LLColor4U>(U16* src, LLColor4U& dst)
+{
+    dst.set(src[0], src[1], src[2], 255);
+}
+
+template<>
+void copyVec4<F32, LLVector4a>(F32* src, LLVector4a& dst)
+{
+    dst.loadua(src);
+}
+
+// copy from src to dst, stride is the number of bytes between each element in src, count is number of elements to copy
+template<class S, class T>
+void copyVec2(S* src, LLStrider<T> dst, S32 stride, S32 count)
+{
+    for (S32 i = 0; i < count; ++i)
+    {
+        copyVec2(src, *dst);
+        dst++;
+        src = (S*)((U8*)src + stride);
+    }
+}
+
+// copy from src to dst, stride is the number of bytes between each element in src, count is number of elements to copy
+template<class S, class T>
+void copyVec3(S* src, LLStrider<T> dst, S32 stride, S32 count)
+{
+    for (S32 i = 0; i < count; ++i)
+    {
+        copyVec3(src, *dst);
+        dst++;
+        src = (S*)((U8*)src + stride);
+    }
+}
+
+// copy from src to dst, stride is the number of bytes between each element in src, count is number of elements to copy
+template<class S, class T>
+void copyVec4(S* src, LLStrider<T> dst, S32 stride, S32 count)
+{
+    for (S32 i = 0; i < count; ++i)
+    {
+        copyVec3(src, *dst);
+        dst++;
+        src = (S*)((U8*)src + stride);
+    }
+}
+
+template<class S, class T>
+void copyAttributeArray(Asset& asset, const Accessor& accessor, const S* src, LLStrider<T>& dst, S32 byteStride)
+{
+    if (accessor.mType == TINYGLTF_TYPE_VEC2)
+    {
+        S32 stride = byteStride == 0 ? sizeof(S) * 2 : byteStride;
+        copyVec2((S*)src, dst, stride, accessor.mCount);
+    }
+    else if (accessor.mType == TINYGLTF_TYPE_VEC3)
+    {
+        S32 stride = byteStride == 0 ? sizeof(S) * 3 : byteStride;
+        copyVec3((S*)src, dst, stride, accessor.mCount);
+    }
+    else if (accessor.mType == TINYGLTF_TYPE_VEC4)
+    {
+        S32 stride = byteStride == 0 ? sizeof(S) * 4 : byteStride;
+        copyVec4((S*)src, dst, stride, accessor.mCount);
+    }
+    else
+    {
+        LL_ERRS("GLTF") << "Unsupported accessor type" << LL_ENDL;
+    }
+}
+
+template <class T>
+void Primitive::copyAttribute(Asset& asset, S32 accessorIdx, LLStrider<T>& dst)
+{
+    const Accessor& accessor = asset.mAccessors[accessorIdx];
+    const BufferView& bufferView = asset.mBufferViews[accessor.mBufferView];
+    const Buffer& buffer = asset.mBuffers[bufferView.mBuffer];
+    const U8* src = buffer.mData.data() + bufferView.mByteOffset + accessor.mByteOffset;
+
+    if (accessor.mComponentType == TINYGLTF_COMPONENT_TYPE_FLOAT)
+    {
+        copyAttributeArray(asset, accessor, (const F32*)src, dst, bufferView.mByteStride);
+    }
+    else if (accessor.mComponentType == TINYGLTF_COMPONENT_TYPE_UNSIGNED_SHORT)
+    {
+        copyAttributeArray(asset, accessor, (const U16*)src, dst, bufferView.mByteStride);
+    }
+    else if (accessor.mComponentType == TINYGLTF_COMPONENT_TYPE_UNSIGNED_INT)
+    {
+        copyAttributeArray(asset, accessor, (const U32*)src, dst, bufferView.mByteStride);
+    }
+    else
+
+    {
+        LL_ERRS() << "Unsupported component type" << LL_ENDL;
+    }
+}
+
+void Primitive::allocateGLResources(Asset& asset)
+{
+    // allocate vertex buffer
+    // We diverge from the intent of the GLTF format here to work with our existing render pipeline
+    // GLTF wants us to copy the buffer views into GPU storage as is and build render commands that source that data.
+    // For our engine, though, it's better to rearrange the buffers at load time into a layout that's more consistent.
+    // The GLTF native approach undoubtedly works well if you can count on VAOs, but VAOs perform much worse with our scenes.
+
+    // get the number of vertices
+    U32 numVertices = 0;
+    for (auto& it : mAttributes)
+    {
+        const Accessor& accessor = asset.mAccessors[it.second];
+        numVertices = accessor.mCount;
+        break;
+    }
+
+    // get the number of indices
+    U32 numIndices = 0;
+    if (mIndices != INVALID_INDEX)
+    {
+        const Accessor& accessor = asset.mAccessors[mIndices];
+        numIndices = accessor.mCount;
+    }
+
+    // create vertex buffer
+    mVertexBuffer = new LLVertexBuffer(ATTRIBUTE_MASK);
+    mVertexBuffer->allocateBuffer(numVertices, numIndices);
+
+    bool needs_color = true;
+    bool needs_texcoord = true;
+    bool needs_normal = true;
+    bool needs_tangent = true;
+
+    // load vertex data
+    for (auto& it : mAttributes)
+    {
+        const std::string& attribName = it.first;
+
+        // load vertex data
+        if (attribName == "POSITION")
+        {
+            // load position data
+            LLStrider<LLVector4a> dst;
+            mVertexBuffer->getVertexStrider(dst);
+
+            copyAttribute(asset, it.second, dst);
+        }
+        else if (attribName == "NORMAL")
+        {
+            needs_normal = false;
+            // load normal data
+            LLStrider<LLVector4a> dst;
+            mVertexBuffer->getNormalStrider(dst);
+
+            copyAttribute(asset, it.second, dst);
+        }
+        else if (attribName == "TANGENT")
+        {
+            needs_tangent = false;
+            // load tangent data
+
+            LLStrider<LLVector4a> dst;
+            mVertexBuffer->getTangentStrider(dst);
+
+            copyAttribute(asset, it.second, dst);
+        }
+        else if (attribName == "COLOR_0")
+        {
+            needs_color = false;
+            // load color data
+
+            LLStrider<LLColor4U> dst;
+            mVertexBuffer->getColorStrider(dst);
+
+            copyAttribute(asset, it.second, dst);
+        }
+        else if (attribName == "TEXCOORD_0")
+        {
+            needs_texcoord = false;
+            // load texcoord data
+            LLStrider<LLVector2> dst;
+            mVertexBuffer->getTexCoord0Strider(dst);
+
+            LLStrider<LLVector2> tc = dst;
+            copyAttribute(asset, it.second, dst);
+
+            // convert to OpenGL coordinate space
+            for (U32 i = 0; i < numVertices; ++i)
+            {
+                tc->mV[1] = 1.0f - tc->mV[1];;
+                tc++;
+            }
+        }
+    }
+
+    // copy index buffer
+    if (mIndices != INVALID_INDEX)
+    {
+        const Accessor& accessor = asset.mAccessors[mIndices];
+        const BufferView& bufferView = asset.mBufferViews[accessor.mBufferView];
+        const Buffer& buffer = asset.mBuffers[bufferView.mBuffer];
+
+        const U8* src = buffer.mData.data() + bufferView.mByteOffset + accessor.mByteOffset;
+
+        LLStrider<U16> dst;
+        mVertexBuffer->getIndexStrider(dst);
+        mIndexArray.resize(numIndices);
+
+        if (accessor.mComponentType == TINYGLTF_COMPONENT_TYPE_UNSIGNED_INT)
+        {
+            for (U32 i = 0; i < numIndices; ++i)
+            {
+                *(dst++) = (U16) * (U32*)src;
+                src += sizeof(U32);
+            }
+        }
+        else if (accessor.mComponentType == TINYGLTF_COMPONENT_TYPE_UNSIGNED_SHORT)
+        {
+            for (U32 i = 0; i < numIndices; ++i)
+            {
+                *(dst++) = *(U16*)src;
+                src += sizeof(U16);
+            }
+        }
+        else
+        {
+            LL_ERRS("GLTF") << "Unsupported component type for indices" << LL_ENDL;
+        }
+
+        U16* idx = (U16*)mVertexBuffer->getMappedIndices();
+        for (U32 i = 0; i < numIndices; ++i)
+        {
+            mIndexArray[i] = idx[i];
+        }
+    }
+
+    // fill in default values for missing attributes
+    if (needs_color)
+    { // set default color
+        LLStrider<LLColor4U> dst;
+        mVertexBuffer->getColorStrider(dst);
+        for (U32 i = 0; i < numVertices; ++i)
+        {
+            *(dst++) = LLColor4U(255, 255, 255, 255);
+        }
+    }
+
+    if (needs_texcoord)
+    { // set default texcoord
+        LLStrider<LLVector2> dst;
+        mVertexBuffer->getTexCoord0Strider(dst);
+        for (U32 i = 0; i < numVertices; ++i)
+        {
+            *(dst++) = LLVector2(0.0f, 0.0f);
+        }
+    }
+
+    if (needs_normal)
+    { // set default normal
+        LLStrider<LLVector4a> dst;
+        mVertexBuffer->getNormalStrider(dst);
+        for (U32 i = 0; i < numVertices; ++i)
+        {
+            *(dst++) = LLVector4a(0.0f, 0.0f, 1.0f, 0.0f);
+        }
+    }
+
+    if (needs_tangent)
+    {  // TODO: generate tangents if needed
+        LLStrider<LLVector4a> dst;
+        mVertexBuffer->getTangentStrider(dst);
+        for (U32 i = 0; i < numVertices; ++i)
+        {
+            *(dst++) = LLVector4a(1.0f, 0.0f, 0.0f, 1.0f);
+        }
+    }
+
+    mPositions.resize(numVertices);
+    mTexCoords.resize(numVertices);
+    mNormals.resize(numVertices);
+    mTangents.resize(numVertices);
+
+    LLVector4a* pos = (LLVector4a*)(mVertexBuffer->getMappedData() + mVertexBuffer->getOffset(LLVertexBuffer::TYPE_VERTEX));
+    LLVector2* tc = (LLVector2*)(mVertexBuffer->getMappedData() + mVertexBuffer->getOffset(LLVertexBuffer::TYPE_TEXCOORD0));
+    LLVector4a* norm = (LLVector4a*)(mVertexBuffer->getMappedData() + mVertexBuffer->getOffset(LLVertexBuffer::TYPE_NORMAL));
+    LLVector4a* tangent = (LLVector4a*)(mVertexBuffer->getMappedData() + mVertexBuffer->getOffset(LLVertexBuffer::TYPE_TANGENT));
+    for (U32 i = 0; i < numVertices; ++i)
+    {
+        mPositions[i] = pos[i];
+        mTexCoords[i] = tc[i];
+        mNormals[i] = norm[i];
+        mTangents[i] = tangent[i];
+    }
+    createOctree();
+    
+    mVertexBuffer->unmapBuffer();
+}
+
+void Primitive::createOctree()
+{
+    // create octree
+    mOctree = new LLVolumeOctree();
+
+    if (mMode == TINYGLTF_MODE_TRIANGLES)
+    {
+        F32 scaler = 0.25f;
+
+        const U32 num_triangles = mVertexBuffer->getNumIndices() / 3;
+        // Initialize all the triangles we need
+        mOctreeTriangles.resize(num_triangles);
+
+        LLVector4a* pos = (LLVector4a*)(mVertexBuffer->getMappedData() + mVertexBuffer->getOffset(LLVertexBuffer::TYPE_VERTEX));
+        U16* indices = (U16*)mVertexBuffer->getMappedIndices();
+
+        for (U32 triangle_index = 0; triangle_index < num_triangles; ++triangle_index)
+        { //for each triangle
+            const U32 index = triangle_index * 3;
+            LLVolumeTriangle* tri = &mOctreeTriangles[triangle_index];
+            const LLVector4a& v0 = pos[indices[index]];
+            const LLVector4a& v1 = pos[indices[index + 1]];
+            const LLVector4a& v2 = pos[indices[index + 2]];
+
+            //store pointers to vertex data
+            tri->mV[0] = &v0;
+            tri->mV[1] = &v1;
+            tri->mV[2] = &v2;
+
+            //store indices
+            tri->mIndex[0] = indices[index];
+            tri->mIndex[1] = indices[index + 1];
+            tri->mIndex[2] = indices[index + 2];
+
+            //get minimum point
+            LLVector4a min = v0;
+            min.setMin(min, v1);
+            min.setMin(min, v2);
+
+            //get maximum point
+            LLVector4a max = v0;
+            max.setMax(max, v1);
+            max.setMax(max, v2);
+
+            //compute center
+            LLVector4a center;
+            center.setAdd(min, max);
+            center.mul(0.5f);
+
+            tri->mPositionGroup = center;
+
+            //compute "radius"
+            LLVector4a size;
+            size.setSub(max, min);
+
+            tri->mRadius = size.getLength3().getF32() * scaler;
+
+            //insert
+            mOctree->insert(tri);
+        }
+    }
+    else
+    {
+        LL_ERRS() << "Unsupported Primitive mode" << LL_ENDL;
+    }
+
+    //remove unneeded octree layers
+    while (!mOctree->balance()) {}
+
+    //calculate AABB for each node
+    LLVolumeOctreeRebound rebound;
+    rebound.traverse(mOctree);
+}
+
+const LLVolumeTriangle* Primitive::lineSegmentIntersect(const LLVector4a& start, const LLVector4a& end,
+    LLVector4a* intersection, LLVector2* tex_coord, LLVector4a* normal, LLVector4a* tangent_out)
+{
+    if (mOctree.isNull())
+    {
+        return nullptr;
+    }
+
+    LLVector4a dir;
+    dir.setSub(end, start);
+
+    F32 closest_t = 2.f; // must be larger than 1
+
+    //create a proxy LLVolumeFace for the raycast
+    LLVolumeFace face;
+    face.mPositions = mPositions.data();
+    face.mTexCoords = mTexCoords.data();
+    face.mNormals = mNormals.data();
+    face.mTangents = mTangents.data();
+    face.mIndices = mIndexArray.data();
+
+    face.mNumIndices = mIndexArray.size();
+    face.mNumVertices = mPositions.size();
+
+    LLOctreeTriangleRayIntersect intersect(start, dir, &face, &closest_t, intersection, tex_coord, normal, tangent_out);
+    intersect.traverse(mOctree);
+
+    // null out proxy data so it doesn't get freed
+    face.mPositions = face.mNormals = face.mTangents = nullptr;
+    face.mIndices = nullptr;
+    face.mTexCoords = nullptr;
+
+    return intersect.mHitTriangle;
+}
+
+Primitive::~Primitive()
+{
+    mOctree = nullptr;
+}
+
diff --git a/indra/newview/gltf/primitive.h b/indra/newview/gltf/primitive.h
new file mode 100644
index 0000000000..7c47d9dac5
--- /dev/null
+++ b/indra/newview/gltf/primitive.h
@@ -0,0 +1,140 @@
+#pragma once
+
+/**
+ * @file primitive.h
+ * @brief LL GLTF Implementation
+ *
+ * $LicenseInfo:firstyear=2024&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2024, Linden Research, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#include "llvertexbuffer.h"
+#include "llvolumeoctree.h"
+
+// LL GLTF Implementation
+namespace LL
+{
+    namespace GLTF
+    {
+        class Asset;
+
+        constexpr U32 ATTRIBUTE_MASK =
+            LLVertexBuffer::MAP_VERTEX |
+            LLVertexBuffer::MAP_NORMAL |
+            LLVertexBuffer::MAP_TEXCOORD0 |
+            LLVertexBuffer::MAP_TANGENT |
+            LLVertexBuffer::MAP_COLOR;
+
+        class Primitive
+        {
+        public:
+            ~Primitive();
+
+            // GPU copy of mesh data
+            LLPointer<LLVertexBuffer> mVertexBuffer;
+
+            // CPU copy of mesh data
+            std::vector<LLVector2> mTexCoords;
+            std::vector<LLVector4a> mNormals;
+            std::vector<LLVector4a> mTangents;
+            std::vector<LLVector4a> mPositions;
+            std::vector<U16> mIndexArray;
+
+            // raycast acceleration structure
+            LLPointer<LLVolumeOctree> mOctree;
+            std::vector<LLVolumeTriangle> mOctreeTriangles;
+            
+            S32 mMaterial = -1;
+            U32 mMode = TINYGLTF_MODE_TRIANGLES; // default to triangles
+            U32 mGLMode = LLRender::TRIANGLES;
+            S32 mIndices = -1;
+            std::unordered_map<std::string, int> mAttributes;
+
+            // copy the attribute in the given BufferView to the given destination
+            // assumes destination has enough storage for the attribute
+            template<class T>
+            void copyAttribute(Asset& asset, S32 bufferViewIdx, LLStrider<T>& dst);
+            
+            // create octree based on vertex buffer
+            // must be called before buffer is unmapped and after buffer is populated with good data
+            void createOctree();
+
+            //get the LLVolumeTriangle that intersects with the given line segment at the point 
+            //closest to start.  Moves end to the point of intersection.  Returns nullptr if no intersection.
+            //Line segment must be in the same coordinate frame as this Primitive
+            const LLVolumeTriangle* lineSegmentIntersect(const LLVector4a& start, const LLVector4a& end,
+                LLVector4a* intersection = NULL,         // return the intersection point
+                LLVector2* tex_coord = NULL,            // return the texture coordinates of the intersection point
+                LLVector4a* normal = NULL,               // return the surface normal at the intersection point
+                LLVector4a* tangent = NULL             // return the surface tangent at the intersection point
+            );
+            
+            const Primitive& operator=(const tinygltf::Primitive& src)
+            {
+                // load material
+                mMaterial = src.material;
+
+                // load mode
+                mMode = src.mode;
+
+                // load indices
+                mIndices = src.indices;
+
+                // load attributes
+                for (auto& it : src.attributes)
+                {
+                    mAttributes[it.first] = it.second;
+                }
+
+                switch (mMode)
+                {
+                case TINYGLTF_MODE_POINTS:
+                    mGLMode = LLRender::POINTS;
+                    break;
+                case TINYGLTF_MODE_LINE:
+                    mGLMode = LLRender::LINES;
+                    break;
+                case TINYGLTF_MODE_LINE_LOOP:
+                    mGLMode = LLRender::LINE_LOOP;
+                    break;
+                case TINYGLTF_MODE_LINE_STRIP:
+                    mGLMode = LLRender::LINE_STRIP;
+                    break;
+                case TINYGLTF_MODE_TRIANGLES:
+                    mGLMode = LLRender::TRIANGLES;
+                    break;
+                case TINYGLTF_MODE_TRIANGLE_STRIP:
+                    mGLMode = LLRender::TRIANGLE_STRIP;
+                    break;
+                case TINYGLTF_MODE_TRIANGLE_FAN:
+                    mGLMode = LLRender::TRIANGLE_FAN;
+                    break;
+                default:
+                    mGLMode = GL_TRIANGLES;
+                }
+
+                return *this;
+            }
+
+            void allocateGLResources(Asset& asset);
+        };
+    }
+}