From b087e2554f6091cb222ae1462ebb927b19b6414b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lars=20M=C3=BCller?=
 <34514239+appgurueu@users.noreply.github.com>
Date: Tue, 24 Dec 2024 15:25:07 +0100
Subject: [PATCH] Add glTF STEP interpolation support (#15525)

---
 doc/lua_api.md                                |   2 +-
 games/devtest/mods/gltf/init.lua              |  14 +++++++++
 .../gltf/models/gltf_simple_skin_step.gltf    | Bin 0 -> 2710 bytes
 irr/src/CGLTFMeshFileLoader.cpp               |  27 ++++++++++++++----
 4 files changed, 36 insertions(+), 7 deletions(-)
 create mode 100644 games/devtest/mods/gltf/models/gltf_simple_skin_step.gltf

diff --git a/doc/lua_api.md b/doc/lua_api.md
index 91d8f314a..f46c9eb28 100644
--- a/doc/lua_api.md
+++ b/doc/lua_api.md
@@ -318,7 +318,7 @@ Many glTF features are not supported *yet*, including:
 
 * Animations
   * Only a single animation is supported, use frame ranges within this animation.
-  * Only linear interpolation is supported.
+  * `CUBICSPLINE` interpolation is not supported.
 * Cameras
 * Materials
   * Only base color textures are supported
diff --git a/games/devtest/mods/gltf/init.lua b/games/devtest/mods/gltf/init.lua
index fd4d13bee..f6a8f9bdf 100644
--- a/games/devtest/mods/gltf/init.lua
+++ b/games/devtest/mods/gltf/init.lua
@@ -55,6 +55,20 @@ core.register_entity("gltf:simple_skin", {
 	end
 })
 
+core.register_entity("gltf:simple_skin_step", {
+	initial_properties = {
+		infotext = "Simple skin, but using STEP interpolation",
+		visual = "mesh",
+		visual_size = vector.new(5, 5, 5),
+		mesh = "gltf_simple_skin_step.gltf",
+		textures = {},
+		backface_culling = false
+	},
+	on_activate = function(self)
+		self.object:set_animation({x = 0, y = 5.5}, 1)
+	end
+})
+
 -- The claws rendering incorrectly from one side is expected behavior:
 -- They use an unsupported double-sided material.
 core.register_entity("gltf:frog", {
diff --git a/games/devtest/mods/gltf/models/gltf_simple_skin_step.gltf b/games/devtest/mods/gltf/models/gltf_simple_skin_step.gltf
new file mode 100644
index 0000000000000000000000000000000000000000..f26c0c8b1101fee094d67aa4ce0ecbf03b5b8f5c
GIT binary patch
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diff --git a/irr/src/CGLTFMeshFileLoader.cpp b/irr/src/CGLTFMeshFileLoader.cpp
index 79c68355b..4e653fbf8 100644
--- a/irr/src/CGLTFMeshFileLoader.cpp
+++ b/irr/src/CGLTFMeshFileLoader.cpp
@@ -677,8 +677,17 @@ void SelfType::MeshExtractor::loadAnimation(const std::size_t 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, only linear interpolation is supported");
+
+		bool interpolate = ([&]() {
+			switch (sampler.interpolation) {
+				case tiniergltf::AnimationSampler::Interpolation::STEP:
+					return false;
+				case tiniergltf::AnimationSampler::Interpolation::LINEAR:
+					return true;
+				default:
+					throw std::runtime_error("Only STEP and LINEAR keyframe interpolation are supported");
+			}
+		})();
 
 		const auto inputAccessor = Accessor<f32>::make(m_gltf_model, sampler.input);
 		const auto n_frames = inputAccessor.getCount();
@@ -686,32 +695,38 @@ void SelfType::MeshExtractor::loadAnimation(const std::size_t animIdx)
 		if (!channel.target.node.has_value())
 			throw std::runtime_error("no animated node");
 
-		const auto &joint = m_loaded_nodes.at(*channel.target.node);
+		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);
+			auto &channel = joint->keys.position;
+			channel.interpolate = interpolate;
 			for (std::size_t i = 0; i < n_frames; ++i) {
 				f32 frame = inputAccessor.get(i);
 				core::vector3df position = outputAccessor.get(i);
-				m_irr_model->addPositionKey(joint, frame, convertHandedness(position));
+				channel.pushBack(frame, convertHandedness(position));
 			}
 			break;
 		}
 		case tiniergltf::AnimationChannelTarget::Path::ROTATION: {
 			const auto outputAccessor = Accessor<core::quaternion>::make(m_gltf_model, sampler.output);
+			auto &channel = joint->keys.rotation;
+			channel.interpolate = interpolate;
 			for (std::size_t i = 0; i < n_frames; ++i) {
 				f32 frame = inputAccessor.get(i);
 				core::quaternion rotation = outputAccessor.get(i);
-				m_irr_model->addRotationKey(joint, frame, convertHandedness(rotation));
+				channel.pushBack(frame, convertHandedness(rotation));
 			}
 			break;
 		}
 		case tiniergltf::AnimationChannelTarget::Path::SCALE: {
 			const auto outputAccessor = Accessor<core::vector3df>::make(m_gltf_model, sampler.output);
+			auto &channel = joint->keys.scale;
+			channel.interpolate = interpolate;
 			for (std::size_t i = 0; i < n_frames; ++i) {
 				f32 frame = inputAccessor.get(i);
 				core::vector3df scale = outputAccessor.get(i);
-				m_irr_model->addScaleKey(joint, frame, scale);
+				channel.pushBack(frame, scale);
 			}
 			break;
 		}