Add glTF animation support

.gitattributes

@@ -3,3 +3,5 @@
 
 *.cpp diff=cpp
 *.h diff=cpp
+
+*.gltf binary

doc/lua_api.md

@@ -294,7 +294,7 @@ depends on by supplying a file with an equal name.
 Only a subset of model file format features is supported:
 
 Simple textured meshes (with multiple textures), optionally with normals.
-The .x and .b3d formats additionally support skeletal animation.
+The .x, .b3d and .gltf formats additionally support (a single) animation.
 
 #### glTF
 
@@ -307,7 +307,10 @@ due to their space savings.
 
 This means that many glTF features are not supported *yet*, including:
 
-* Animation
+* Animations
+  * Only a single animation is supported,
+    use frame ranges within this animation.
+  * Only integer frames are supported.
 * Cameras
 * Materials
   * Only base color textures are supported

games/devtest/mods/gltf/LICENSE.md

@@ -1,4 +1,4 @@
-glTF test model (and corresponding texture) licenses:
+The glTF test models (and corresponding textures) in this mod are all licensed freely:
 
 * Spider (`gltf_spider.gltf`, `gltf_spider.png`):
   * By [archfan7411](https://github.com/archfan7411)

games/devtest/mods/gltf/init.lua

@@ -27,8 +27,34 @@ do
 		},
 	})
 end
+
 register_entity("snow_man", {"gltf_snow_man.png"})
 register_entity("spider", {"gltf_spider.png"})
+
+minetest.register_entity("gltf:spider_animated", {
+	initial_properties = {
+		visual = "mesh",
+		mesh = "gltf_spider_animated.gltf",
+		textures = {"gltf_spider.png"},
+	},
+	on_activate = function(self)
+		self.object:set_animation({x = 0, y = 140}, 1)
+	end
+})
+
+minetest.register_entity("gltf:simple_skin", {
+	initial_properties = {
+		visual = "mesh",
+		visual_size = vector.new(5, 5, 5),
+		mesh = "gltf_simple_skin.gltf",
+		textures = {},
+		backface_culling = false
+	},
+	on_activate = function(self)
+		self.object:set_animation({x = 0, y = 5.5}, 1)
+	end
+})
+
 -- Note: Model has an animation, but we can use it as a static test nevertheless
 -- The claws rendering incorrectly from one side is expected behavior:
 -- They use an unsupported double-sided material.

games/devtest/mods/gltf/models/gltf_simple_skin.gltf

@@ -0,0 +1 @@
+{"scene":0,"scenes":[{"nodes":[0,1]}],"nodes":[{"skin":0,"mesh":0},{"children":[2]},{"translation":[0.0,1.0,0.0],"rotation":[0.0,0.0,0.0,1.0]}],"meshes":[{"primitives":[{"attributes":{"POSITION":1,"JOINTS_0":2,"WEIGHTS_0":3},"indices":0}]}],"skins":[{"inverseBindMatrices":4,"joints":[1,2]}],"animations":[{"channels":[{"sampler":0,"target":{"node":2,"path":"rotation"}}],"samplers":[{"input":5,"interpolation":"LINEAR","output":6}]}],"buffers":[{"uri":"data:application/gltf-buffer;base64,AAABAAMAAAADAAIAAgADAAUAAgAFAAQABAAFAAcABAAHAAYABgAHAAkABgAJAAgAAAAAvwAAAAAAAAAAAAAAPwAAAAAAAAAAAAAAvwAAAD8AAAAAAAAAPwAAAD8AAAAAAAAAvwAAgD8AAAAAAAAAPwAAgD8AAAAAAAAAvwAAwD8AAAAAAAAAPwAAwD8AAAAAAAAAvwAAAEAAAAAAAAAAPwAAAEAAAAAA","byteLength":168},{"uri":"data:application/gltf-buffer;base64,AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAABAPwAAgD4AAAAAAAAAAAAAQD8AAIA+AAAAAAAAAAAAAAA/AAAAPwAAAAAAAAAAAAAAPwAAAD8AAAAAAAAAAAAAgD4AAEA/AAAAAAAAAAAAAIA+AABAPwAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAA=","byteLength":320},{"uri":"data:application/gltf-buffer;base64,AACAPwAAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAAAAAAAAAAACAPwAAgD8AAAAAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAIC/AAAAAAAAgD8=","byteLength":128},{"uri":"data:application/gltf-buffer;base64,AAAAAAAAAD8AAIA/AADAPwAAAEAAACBAAABAQAAAYEAAAIBAAACQQAAAoEAAALBAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAkxjEPkSLbD8AAAAAAAAAAPT9ND/0/TQ/AAAAAAAAAAD0/TQ/9P00PwAAAAAAAAAAkxjEPkSLbD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAkxjEvkSLbD8AAAAAAAAAAPT9NL/0/TQ/AAAAAAAAAAD0/TS/9P00PwAAAAAAAAAAkxjEvkSLbD8AAAAAAAAAAAAAAAAAAIA/","byteLength":240}],"bufferViews":[{"buffer":0,"byteLength":48,"target":34963},{"buffer":0,"byteOffset":48,"byteLength":120,"target":34962},{"buffer":1,"byteLength":320,"byteStride":16},{"buffer":2,"byteLength":128},{"buffer":3,"byteLength":240}],"accessors":[{"bufferView":0,"componentType":5123,"count":24,"type":"SCALAR"},{"bufferView":1,"componentType":5126,"count":10,"type":"VEC3","max":[0.5,2.0,0.0],"min":[-0.5,0.0,0.0]},{"bufferView":2,"componentType":5123,"count":10,"type":"VEC4"},{"bufferView":2,"byteOffset":160,"componentType":5126,"count":10,"type":"VEC4"},{"bufferView":3,"componentType":5126,"count":2,"type":"MAT4"},{"bufferView":4,"componentType":5126,"count":12,"type":"SCALAR","max":[5.5],"min":[0.0]},{"bufferView":4,"byteOffset":48,"componentType":5126,"count":12,"type":"VEC4","max":[0.0,0.0,0.707,1.0],"min":[0.0,0.0,-0.707,0.707]}],"asset":{"version":"2.0"}}

irr/src/CGLTFMeshFileLoader.cpp

@@ -6,9 +6,9 @@
 #include "SMaterialLayer.h"
 #include "coreutil.h"
 #include "CSkinnedMesh.h"
-#include "ISkinnedMesh.h"
-#include "irrTypes.h"
+#include "IAnimatedMesh.h"
 #include "IReadFile.h"
+#include "irrTypes.h"
 #include "matrix4.h"
 #include "path.h"
 #include "quaternion.h"
@@ -23,9 +23,11 @@
 #include <memory>
 #include <optional>
 #include <stdexcept>
+#include <tuple>
 #include <utility>
 #include <variant>
 #include <vector>
+#include <iostream>
 
 namespace irr {
 
@@ -51,6 +53,28 @@ core::vector3df convertHandedness(const core::vector3df &p)
 	return core::vector3df(p.X, p.Y, -p.Z);
 }
 
+template <>
+core::quaternion convertHandedness(const core::quaternion &q)
+{
+	return core::quaternion(q.X, q.Y, -q.Z, q.W);
+}
+
+template <>
+core::matrix4 convertHandedness(const core::matrix4 &mat)
+{
+	// Base transformation between left & right handed coordinate systems.
+	static const core::matrix4 invertZ = core::matrix4(
+			1, 0, 0, 0,
+			0, 1, 0, 0,
+			0, 0, -1, 0,
+			0, 0, 0, 1);
+	// Convert from left-handed to right-handed,
+	// then apply mat,
+	// then convert from right-handed to left-handed.
+	// Both conversions just invert Z.
+	return invertZ * mat * invertZ;
+}
+
 namespace scene {
 
 using SelfType = CGLTFMeshFileLoader;
@@ -196,6 +220,8 @@ ACCESSOR_PRIMITIVE(u16, UNSIGNED_SHORT)
 ACCESSOR_PRIMITIVE(u32, UNSIGNED_INT)
 
 ACCESSOR_TYPES(core::vector3df, VEC3, FLOAT)
+ACCESSOR_TYPES(core::quaternion, VEC4, FLOAT)
+ACCESSOR_TYPES(core::matrix4, MAT4, FLOAT)
 
 template <class T>
 T SelfType::Accessor<T>::get(std::size_t i) const
@@ -340,7 +366,7 @@ IAnimatedMesh* SelfType::createMesh(io::IReadFile* file)
 	auto *mesh = new CSkinnedMesh();
 	MeshExtractor parser(std::move(model.value()), mesh);
 	try {
-		parser.loadNodes();
+		parser.load();
 	} catch (std::runtime_error &e) {
 		os::Printer::log("glTF loader", e.what(), ELL_ERROR);
 		mesh->drop();
@@ -397,61 +423,134 @@ static video::E_TEXTURE_CLAMP convertTextureWrap(const Wrap wrap) {
     }
 }
 
-/**
- * Load up the rawest form of the model. The vertex positions and indices.
- * Documentation: https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes
- * If material is undefined, then a default material MUST be used.
-*/
-void SelfType::MeshExtractor::loadMesh(
-		const std::size_t meshIdx,
-		ISkinnedMesh::SJoint *parent) const
+void SelfType::MeshExtractor::addPrimitive(
+		const tiniergltf::MeshPrimitive &primitive,
+		const std::optional<std::size_t> skinIdx,
+		CSkinnedMesh::SJoint *parent)
 {
-	for (std::size_t pi = 0; pi < getPrimitiveCount(meshIdx); ++pi) {
-		const auto &primitive = m_gltf_model.meshes->at(meshIdx).primitives.at(pi);
-		auto vertices = getVertices(primitive);
-		if (!vertices.has_value())
-			continue; // "When positions are not specified, client implementations SHOULD skip primitive’s rendering"
+	auto vertices = getVertices(primitive);
+	if (!vertices.has_value())
+		return; // "When positions are not specified, client implementations SHOULD skip primitive’s rendering"
 
-		// Excludes the max value for consistency.
-		if (vertices->size() >= std::numeric_limits<u16>::max())
-			throw std::runtime_error("too many vertices");
+	const auto n_vertices = vertices->size();
 
-		// Apply the global transform along the parent chain.
-		transformVertices(*vertices, parent->GlobalMatrix);
+	// Excludes the max value for consistency.
+	if (n_vertices >= std::numeric_limits<u16>::max())
+		throw std::runtime_error("too many vertices");
 
-		auto maybeIndices = getIndices(primitive);
-		std::vector<u16> indices;
-		if (maybeIndices.has_value()) {
-			indices = std::move(*maybeIndices);
-			checkIndices(indices, vertices->size());
-		} else {
-			// Non-indexed geometry
-			indices = generateIndices(vertices->size());
-		}
+	// Apply the global transform along the parent chain.
+	transformVertices(*vertices, parent->GlobalMatrix);
 
-		m_irr_model->addMeshBuffer(
-				new SSkinMeshBuffer(std::move(*vertices), std::move(indices)));
-		auto *meshbuf = m_irr_model->getMeshBuffer(m_irr_model->getMeshBufferCount() - 1);
-		auto &irr_mat = meshbuf->getMaterial();
+	auto maybeIndices = getIndices(primitive);
+	std::vector<u16> indices;
+	if (maybeIndices.has_value()) {
+		indices = std::move(*maybeIndices);
+		checkIndices(indices, vertices->size());
+	} else {
+		// Non-indexed geometry
+		indices = generateIndices(vertices->size());
+	}
 
-		if (primitive.material.has_value()) {
-			const auto &material = m_gltf_model.materials->at(*primitive.material);
-			if (material.pbrMetallicRoughness.has_value()) {
-				const auto &texture = material.pbrMetallicRoughness->baseColorTexture;
-				if (texture.has_value()) {
-					const auto meshbufNr = m_irr_model->getMeshBufferCount() - 1;
-					m_irr_model->setTextureSlot(meshbufNr, static_cast<u32>(texture->index));
-					const auto samplerIdx = m_gltf_model.textures->at(texture->index).sampler;
-					if (samplerIdx.has_value()) {
-						auto &sampler = m_gltf_model.samplers->at(*samplerIdx);
-						auto &layer = irr_mat.TextureLayers[0];
-						layer.TextureWrapU = convertTextureWrap(sampler.wrapS);
-						layer.TextureWrapV = convertTextureWrap(sampler.wrapT);
-					}
+	m_irr_model->addMeshBuffer(
+			new SSkinMeshBuffer(std::move(*vertices), std::move(indices)));
+	const auto meshbufNr = m_irr_model->getMeshBufferCount() - 1;
+	auto *meshbuf = m_irr_model->getMeshBuffer(meshbufNr);
+
+	if (primitive.material.has_value()) {
+		const auto &material = m_gltf_model.materials->at(*primitive.material);
+		if (material.pbrMetallicRoughness.has_value()) {
+			const auto &texture = material.pbrMetallicRoughness->baseColorTexture;
+			if (texture.has_value()) {
+				m_irr_model->setTextureSlot(meshbufNr, static_cast<u32>(texture->index));
+				const auto samplerIdx = m_gltf_model.textures->at(texture->index).sampler;
+				if (samplerIdx.has_value()) {
+					auto &sampler = m_gltf_model.samplers->at(*samplerIdx);
+					auto &layer = meshbuf->getMaterial().TextureLayers[0];
+					layer.TextureWrapU = convertTextureWrap(sampler.wrapS);
+					layer.TextureWrapV = convertTextureWrap(sampler.wrapT);
 				}
 			}
 		}
 	}
+
+	if (!skinIdx.has_value()) {
+		// No skin => all vertices belong entirely to their parent
+		for (std::size_t v = 0; v < n_vertices; ++v) {
+			auto *weight = m_irr_model->addWeight(parent);
+			weight->buffer_id = meshbufNr;
+			weight->vertex_id = v;
+			weight->strength = 1.0f;
+		}
+		return;
+	}
+
+	const auto &skin = m_gltf_model.skins->at(*skinIdx);
+
+	const auto &attrs = primitive.attributes;
+	const auto &joints = attrs.joints;
+	if (!joints.has_value())
+		return;
+
+	const auto &weights = attrs.weights;
+	for (std::size_t set = 0; set < joints->size(); ++set) {
+		const auto jointAccessor = ([&]() -> ArrayAccessorVariant<4, u8, u16> {
+			const auto idx = joints->at(set);
+			const auto &acc = m_gltf_model.accessors->at(idx);
+
+			switch (acc.componentType) {
+			case tiniergltf::Accessor::ComponentType::UNSIGNED_BYTE:
+				return Accessor<std::array<u8, 4>>::make(m_gltf_model, idx);
+			case tiniergltf::Accessor::ComponentType::UNSIGNED_SHORT:
+				return Accessor<std::array<u16, 4>>::make(m_gltf_model, idx);
+			default:
+				throw std::runtime_error("invalid component type");
+			}
+		})();
+
+		const auto weightAccessor = createNormalizedValuesAccessor<4>(m_gltf_model, weights->at(set));
+
+		for (std::size_t v = 0; v < n_vertices; ++v) {
+			std::array<u16, 4> jointIdxs;
+			if (std::holds_alternative<Accessor<std::array<u8, 4>>>(jointAccessor)) {
+				const auto jointIdxsU8 = std::get<Accessor<std::array<u8, 4>>>(jointAccessor).get(v);
+				jointIdxs = {jointIdxsU8[0], jointIdxsU8[1], jointIdxsU8[2], jointIdxsU8[3]};
+			} else if (std::holds_alternative<Accessor<std::array<u16, 4>>>(jointAccessor)) {
+				jointIdxs = std::get<Accessor<std::array<u16, 4>>>(jointAccessor).get(v);
+			}
+			std::array<f32, 4> strengths = getNormalizedValues(weightAccessor, v);
+
+			// 4 joints per set
+			for (std::size_t in_set = 0; in_set < 4; ++in_set) {
+				u16 jointIdx = jointIdxs[in_set];
+				f32 strength = strengths[in_set];
+				if (strength == 0)
+					continue;
+
+				CSkinnedMesh::SWeight *weight = m_irr_model->addWeight(m_loaded_nodes.at(skin.joints.at(jointIdx)));
+				weight->buffer_id = meshbufNr;
+				weight->vertex_id = v;
+				weight->strength = strength;
+			}
+		}
+	}
+}
+
+/**
+ * Load up the rawest form of the model. The vertex positions and indices.
+ * Documentation: https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes
+ * If material is undefined, then a default material MUST be used.
+ */
+void SelfType::MeshExtractor::deferAddMesh(
+		const std::size_t meshIdx,
+		const std::optional<std::size_t> skinIdx,
+		CSkinnedMesh::SJoint *parent)
+{
+	m_mesh_loaders.emplace_back([=] {
+		for (std::size_t pi = 0; pi < getPrimitiveCount(meshIdx); ++pi) {
+			const auto &primitive = m_gltf_model.meshes->at(meshIdx).primitives.at(pi);
+			addPrimitive(primitive, skinIdx, parent);
+		}
+	});
 }
 
 // Base transformation between left & right handed coordinate systems.
@@ -464,51 +563,75 @@ static const core::matrix4 leftToRight = core::matrix4(
 );
 static const core::matrix4 rightToLeft = leftToRight;
 
-static core::matrix4 loadTransform(const tiniergltf::Node::Matrix &m)
+static core::matrix4 loadTransform(const tiniergltf::Node::Matrix &m, CSkinnedMesh::SJoint *joint)
 {
 	// Note: Under the hood, this casts these doubles to floats.
-	return core::matrix4(
+	core::matrix4 mat = convertHandedness(core::matrix4(
 			m[0], m[1], m[2], m[3],
 			m[4], m[5], m[6], m[7],
 			m[8], m[9], m[10], m[11],
-			m[12], m[13], m[14], m[15]);
+			m[12], m[13], m[14], m[15]));
+
+	// Decompose the matrix into translation, scale, and rotation.
+	joint->Animatedposition = mat.getTranslation();
+
+	auto scale = mat.getScale();
+	joint->Animatedscale = scale;
+	core::matrix4 inverseScale;
+	inverseScale.setScale(core::vector3df(
+			scale.X == 0 ? 0 : 1 / scale.X,
+			scale.Y == 0 ? 0 : 1 / scale.Y,
+			scale.Z == 0 ? 0 : 1 / scale.Z));
+
+	core::matrix4 axisNormalizedMat = inverseScale * mat;
+	joint->Animatedrotation = axisNormalizedMat.getRotationDegrees();
+	// Invert the rotation because it is applied using `getMatrix_transposed`,
+	// which again inverts.
+	joint->Animatedrotation.makeInverse();
+
+	return mat;
 }
 
-static core::matrix4 loadTransform(const tiniergltf::Node::TRS &trs)
+static core::matrix4 loadTransform(const tiniergltf::Node::TRS &trs, CSkinnedMesh::SJoint *joint)
 {
 	const auto &trans = trs.translation;
 	const auto &rot = trs.rotation;
 	const auto &scale = trs.scale;
 	core::matrix4 transMat;
-	transMat.setTranslation(core::vector3df(trans[0], trans[1], trans[2]));
-	core::matrix4 rotMat = core::quaternion(rot[0], rot[1], rot[2], rot[3]).getMatrix();
+	joint->Animatedposition = convertHandedness(core::vector3df(trans[0], trans[1], trans[2]));
+	transMat.setTranslation(joint->Animatedposition);
+	core::matrix4 rotMat;
+	joint->Animatedrotation = convertHandedness(core::quaternion(rot[0], rot[1], rot[2], rot[3]));
+	core::quaternion(joint->Animatedrotation).getMatrix_transposed(rotMat);
+	joint->Animatedscale = core::vector3df(scale[0], scale[1], scale[2]);
 	core::matrix4 scaleMat;
-	scaleMat.setScale(core::vector3df(scale[0], scale[1], scale[2]));
+	scaleMat.setScale(joint->Animatedscale);
 	return transMat * rotMat * scaleMat;
 }
 
-static core::matrix4 loadTransform(std::optional<std::variant<tiniergltf::Node::Matrix, tiniergltf::Node::TRS>> transform) {
+static core::matrix4 loadTransform(std::optional<std::variant<tiniergltf::Node::Matrix, tiniergltf::Node::TRS>> transform,
+		CSkinnedMesh::SJoint *joint) {
 	if (!transform.has_value()) {
 		return core::matrix4();
 	}
-	core::matrix4 mat = std::visit([](const auto &t) { return loadTransform(t); }, *transform);
-	return rightToLeft * mat * leftToRight;
+	return std::visit([joint](const auto &t) { return loadTransform(t, joint); }, *transform);
 }
 
 void SelfType::MeshExtractor::loadNode(
 		const std::size_t nodeIdx,
-		ISkinnedMesh::SJoint *parent) const
+		CSkinnedMesh::SJoint *parent)
 {
 	const auto &node = m_gltf_model.nodes->at(nodeIdx);
 	auto *joint = m_irr_model->addJoint(parent);
-	const core::matrix4 transform = loadTransform(node.transform);
+	const core::matrix4 transform = loadTransform(node.transform, joint);
 	joint->LocalMatrix = transform;
 	joint->GlobalMatrix = parent ? parent->GlobalMatrix * joint->LocalMatrix : joint->LocalMatrix;
 	if (node.name.has_value()) {
 		joint->Name = node.name->c_str();
 	}
+	m_loaded_nodes[nodeIdx] = joint;
 	if (node.mesh.has_value()) {
-		loadMesh(*node.mesh, joint);
+		deferAddMesh(*node.mesh, node.skin, joint);
 	}
 	if (node.children.has_value()) {
 		for (const auto &child : *node.children) {
@@ -517,8 +640,10 @@ void SelfType::MeshExtractor::loadNode(
 	}
 }
 
-void SelfType::MeshExtractor::loadNodes() const
+void SelfType::MeshExtractor::loadNodes()
 {
+	m_loaded_nodes = std::vector<CSkinnedMesh::SJoint *>(m_gltf_model.nodes->size());
+
 	std::vector<bool> isChild(m_gltf_model.nodes->size());
 	for (const auto &node : *m_gltf_model.nodes) {
 		if (!node.children.has_value())
@@ -536,6 +661,92 @@ void SelfType::MeshExtractor::loadNodes() const
 	}
 }
 
+void SelfType::MeshExtractor::loadSkins()
+{
+	if (!m_gltf_model.skins.has_value())
+		return;
+
+	for (const auto &skin : *m_gltf_model.skins) {
+		if (!skin.inverseBindMatrices.has_value())
+			continue;
+		const auto accessor = Accessor<core::matrix4>::make(m_gltf_model, *skin.inverseBindMatrices);
+		if (accessor.getCount() < skin.joints.size())
+			throw std::runtime_error("accessor contains too few matrices");
+		for (std::size_t i = 0; i < skin.joints.size(); ++i) {
+			m_loaded_nodes.at(skin.joints[i])->GlobalInversedMatrix = convertHandedness(accessor.get(i));
+		}
+	}
+}
+
+void SelfType::MeshExtractor::loadAnimation(const std::size_t animIdx)
+{
+	const auto &anim = m_gltf_model.animations->at(animIdx);
+	for (const auto &channel : anim.channels) {
+
+		const auto &sampler = anim.samplers.at(channel.sampler);
+		if (sampler.interpolation != tiniergltf::AnimationSampler::Interpolation::LINEAR)
+			throw std::runtime_error("unsupported interpolation");
+
+		const auto inputAccessor = Accessor<f32>::make(m_gltf_model, sampler.input);
+		const auto n_frames = inputAccessor.getCount();
+
+		if (!channel.target.node.has_value())
+			throw std::runtime_error("no animated node");
+
+		const auto &joint = m_loaded_nodes.at(*channel.target.node);
+		switch (channel.target.path) {
+		case tiniergltf::AnimationChannelTarget::Path::TRANSLATION: {
+			const auto outputAccessor = Accessor<core::vector3df>::make(m_gltf_model, sampler.output);
+			for (std::size_t i = 0; i < n_frames; ++i) {
+				auto *key = m_irr_model->addPositionKey(joint);
+				key->frame = inputAccessor.get(i);
+				key->position = convertHandedness(outputAccessor.get(i));
+			}
+			break;
+		}
+		case tiniergltf::AnimationChannelTarget::Path::ROTATION: {
+			const auto outputAccessor = Accessor<core::quaternion>::make(m_gltf_model, sampler.output);
+			for (std::size_t i = 0; i < n_frames; ++i) {
+				auto *key = m_irr_model->addRotationKey(joint);
+				key->frame = inputAccessor.get(i);
+				key->rotation = convertHandedness(outputAccessor.get(i));
+			}
+			break;
+		}
+		case tiniergltf::AnimationChannelTarget::Path::SCALE: {
+			const auto outputAccessor = Accessor<core::vector3df>::make(m_gltf_model, sampler.output);
+			for (std::size_t i = 0; i < n_frames; ++i) {
+				auto *key = m_irr_model->addScaleKey(joint);
+				key->frame = inputAccessor.get(i);
+				key->scale = outputAccessor.get(i);
+			}
+			break;
+		}
+		case tiniergltf::AnimationChannelTarget::Path::WEIGHTS:
+			throw std::runtime_error("no support for morph animations");
+		}
+	}
+}
+
+void SelfType::MeshExtractor::load()
+{
+	loadNodes();
+	for (const auto &load_mesh : m_mesh_loaders) {
+		load_mesh();
+	}
+	loadSkins();
+	// Load the first animation, if there is one.
+	if (m_gltf_model.animations.has_value()) {
+		if (m_gltf_model.animations->size() > 1) {
+			os::Printer::log("glTF loader",
+					"multiple animations are not supported", ELL_WARNING);
+		}
+		loadAnimation(0);
+		m_irr_model->setAnimationSpeed(1);
+	}
+	m_irr_model->finalize();
+}
+
 /**
  * Extracts GLTF mesh indices.
  */
@@ -722,4 +933,3 @@ std::optional<tiniergltf::GlTF> SelfType::tryParseGLTF(io::IReadFile* file)
 } // namespace scene
 
 } // namespace irr
-

irr/src/CGLTFMeshFileLoader.h

@@ -10,9 +10,11 @@
 #include "path.h"
 #include "S3DVertex.h"
 
-#include <tiniergltf.hpp>
+#include "tiniergltf.hpp"
 
+#include <functional>
 #include <cstddef>
+#include <tuple>
 #include <vector>
 
 namespace irr
@@ -26,9 +28,9 @@ class CGLTFMeshFileLoader : public IMeshLoader
 public:
 	CGLTFMeshFileLoader() noexcept {};
 
-	bool isALoadableFileExtension(const io::path& filename) const override;
+	bool isALoadableFileExtension(const io::path &filename) const override;
 
-	IAnimatedMesh* createMesh(io::IReadFile* file) override;
+	IAnimatedMesh *createMesh(io::IReadFile *file) override;
 
 private:
 	template <typename T>
@@ -94,7 +96,8 @@ private:
 			const NormalizedValuesAccessor<N> &accessor,
 			const std::size_t i);
 
-	class MeshExtractor {
+	class MeshExtractor
+	{
 	public:
 		MeshExtractor(tiniergltf::GlTF &&model,
 				CSkinnedMesh *mesh) noexcept
@@ -114,12 +117,15 @@ private:
 
 		std::size_t getPrimitiveCount(const std::size_t meshIdx) const;
 
-		void loadNodes() const;
+		void load();
 
 	private:
 		const tiniergltf::GlTF m_gltf_model;
 		CSkinnedMesh *m_irr_model;
 
+		std::vector<std::function<void()>> m_mesh_loaders;
+		std::vector<CSkinnedMesh::SJoint *> m_loaded_nodes;
+
 		void copyPositions(const std::size_t accessorIdx,
 				std::vector<video::S3DVertex>& vertices) const;
 
@@ -129,16 +135,24 @@ private:
 		void copyTCoords(const std::size_t accessorIdx,
 				std::vector<video::S3DVertex>& vertices) const;
 
-		void loadMesh(
-			std::size_t meshIdx,
-			ISkinnedMesh::SJoint *parentJoint) const;
+		void addPrimitive(const tiniergltf::MeshPrimitive &primitive,
+				const std::optional<std::size_t> skinIdx,
+				CSkinnedMesh::SJoint *parent);
 
-		void loadNode(
-			const std::size_t nodeIdx,
-			ISkinnedMesh::SJoint *parentJoint) const;
+		void deferAddMesh(const std::size_t meshIdx,
+				const std::optional<std::size_t> skinIdx,
+				CSkinnedMesh::SJoint *parentJoint);
+
+		void loadNode(const std::size_t nodeIdx, CSkinnedMesh::SJoint *parentJoint);
+
+		void loadNodes();
+
+		void loadSkins();
+
+		void loadAnimation(const std::size_t animIdx);
 	};
 
-	std::optional<tiniergltf::GlTF> tryParseGLTF(io::IReadFile* file);
+	std::optional<tiniergltf::GlTF> tryParseGLTF(io::IReadFile *file);
 };
 
 } // namespace scene

src/unittest/test_irr_gltf_mesh_loader.cpp

@@ -8,6 +8,7 @@
 #include "irr_v2d.h"
 #include "irr_ptr.h"
 
+#include "ISkinnedMesh.h"
 #include <irrlicht.h>
 
 #include "catch.h"
@@ -371,7 +372,91 @@ SECTION("simple sparse accessor")
 		CHECK(vertices[i].Pos == expectedPositions[i]);
 }
 
+// https://github.com/KhronosGroup/glTF-Sample-Models/tree/main/2.0/SimpleSkin
+SECTION("simple skin")
+{
+	using ISkinnedMesh = irr::scene::ISkinnedMesh;
+	const auto mesh = loadMesh(model_stem + "simple_skin.gltf");
+	REQUIRE(mesh != nullptr);
+	auto csm = dynamic_cast<const ISkinnedMesh*>(mesh);
+	const auto joints = csm->getAllJoints();
+	REQUIRE(joints.size() == 3);
+
+	const auto findJoint = [&](const std::function<bool(ISkinnedMesh::SJoint*)> &predicate) {
+		for (std::size_t i = 0; i < joints.size(); ++i) {
+			if (predicate(joints[i])) {
+				return joints[i];
+			}
+		}
+		throw std::runtime_error("joint not found");
+	};
+
+	// Check the node hierarchy
+	const auto parent = findJoint([](auto joint) {
+		return !joint->Children.empty();
+	});
+	REQUIRE(parent->Children.size() == 1);
+	const auto child = parent->Children[0];
+	REQUIRE(child != parent);
+
+	SECTION("transformations are correct")
+	{
+		CHECK(parent->Animatedposition == v3f(0, 0, 0));
+		CHECK(parent->Animatedrotation == irr::core::quaternion());
+		CHECK(parent->Animatedscale == v3f(1, 1, 1));
+		CHECK(parent->GlobalInversedMatrix == irr::core::matrix4());
+		const v3f childTranslation(0, 1, 0);
+		CHECK(child->Animatedposition == childTranslation);
+		CHECK(child->Animatedrotation == irr::core::quaternion());
+		CHECK(child->Animatedscale == v3f(1, 1, 1));
+		irr::core::matrix4 inverseBindMatrix;
+		inverseBindMatrix.setInverseTranslation(childTranslation);
+		CHECK(child->GlobalInversedMatrix == inverseBindMatrix);
+	}
+
+	SECTION("weights are correct")
+	{
+		const auto weights = [&](const ISkinnedMesh::SJoint *joint) {
+			std::unordered_map<irr::u32, irr::f32> weights;
+			for (std::size_t i = 0; i < joint->Weights.size(); ++i) {
+				const auto weight = joint->Weights[i];
+				REQUIRE(weight.buffer_id == 0);
+				weights[weight.vertex_id] = weight.strength;
+			}
+			return weights;
+		};
+		const auto parentWeights = weights(parent);
+		const auto childWeights = weights(child);
+
+		const auto checkWeights = [&](irr::u32 index, irr::f32 parentWeight, irr::f32 childWeight) {
+			const auto getWeight = [](auto weights, auto index) {
+				const auto it = weights.find(index);
+				return it == weights.end() ? 0.0f : it->second;
+			};
+			CHECK(getWeight(parentWeights, index) == parentWeight);
+			CHECK(getWeight(childWeights, index) == childWeight);
+		};
+		checkWeights(0, 1.00, 0.00);
+		checkWeights(1, 1.00, 0.00);
+		checkWeights(2, 0.75, 0.25);
+		checkWeights(3, 0.75, 0.25);
+		checkWeights(4, 0.50, 0.50);
+		checkWeights(5, 0.50, 0.50);
+		checkWeights(6, 0.25, 0.75);
+		checkWeights(7, 0.25, 0.75);
+		checkWeights(8, 0.00, 1.00);
+		checkWeights(9, 0.00, 1.00);
+	}
+
+	SECTION("there should be a third node not involved in skinning")
+	{
+		const auto other = findJoint([&](auto joint) {
+			return joint != child && joint != parent;
+		});
+		CHECK(other->Weights.empty());
+	}
+}
+
 driver->closeDevice();
 driver->drop();
-
 }