From 46148bbf6196698cf232fd54dda691f41e7e9a8c Mon Sep 17 00:00:00 2001
From: JosiahWI <josiah_vanderzee@mediacombb.net>
Date: Sun, 6 Nov 2022 07:55:09 -0600
Subject: [PATCH] Load vertex coordinates from glTF buffer

---
 source/Irrlicht/CGLTFMeshFileLoader.cpp       | 60 ++++++++++++++++---
 source/Irrlicht/CGLTFMeshFileLoader.h         |  4 +-
 .../tests/testCGLTFMeshFileLoader.cpp         |  4 +-
 3 files changed, 58 insertions(+), 10 deletions(-)

diff --git a/source/Irrlicht/CGLTFMeshFileLoader.cpp b/source/Irrlicht/CGLTFMeshFileLoader.cpp
index 81f4fd8a..540c80a0 100644
--- a/source/Irrlicht/CGLTFMeshFileLoader.cpp
+++ b/source/Irrlicht/CGLTFMeshFileLoader.cpp
@@ -9,10 +9,12 @@
 #include "SAnimatedMesh.h"
 #include "SColor.h"
 #include "SMesh.h"
+#include "vector3d.h"
 
 #define TINYGLTF_IMPLEMENTATION
 #include <tiny_gltf.h>
 
+#include <cstddef>
 #include <memory>
 #include <string>
 
@@ -22,6 +24,33 @@ namespace irr
 namespace scene
 {
 
+class BufferOffset
+{
+public:
+	BufferOffset(const std::vector<unsigned char>& buf,
+			const std::size_t offset) noexcept
+		: m_buf(buf), m_offset(offset)
+	{
+	}
+
+	unsigned char at(const std::size_t fromOffset) const
+	{
+		return m_buf.at(m_offset + fromOffset);
+	}
+
+private:
+	const std::vector<unsigned char>& m_buf;
+	std::size_t m_offset;
+};
+
+static constexpr float readFloat(const BufferOffset& readFrom) {
+	unsigned char d[4]{};
+	for (int i = 0; i < 4; ++i) {
+		d[i] = readFrom.at(i);
+	}
+	return *reinterpret_cast<float*>(d);
+}
+
 CGLTFMeshFileLoader::CGLTFMeshFileLoader()
 {
 }
@@ -34,18 +63,35 @@ bool CGLTFMeshFileLoader::isALoadableFileExtension(
 
 IAnimatedMesh* CGLTFMeshFileLoader::createMesh(io::IReadFile* file)
 {
-	if (file->getSize() == 0 || !tryParseGLTF(file)) {
+	tinygltf::Model model{};
+
+	if (file->getSize() == 0 || !tryParseGLTF(file, model)) {
 		return nullptr;
 	}
 
+	const auto& view = model.bufferViews[model.accessors[1].bufferView];
+	const auto& buffer = model.buffers[view.buffer];
+	const core::vector3df v1(
+		-readFloat(BufferOffset(buffer.data, view.byteOffset)),
+		readFloat(BufferOffset(buffer.data, view.byteOffset + 4)),
+		readFloat(BufferOffset(buffer.data, view.byteOffset + 8)));
+	const core::vector3df v2(
+		-readFloat(BufferOffset(buffer.data, view.byteOffset + 12)),
+		readFloat(BufferOffset(buffer.data, view.byteOffset + 16)),
+		readFloat(BufferOffset(buffer.data, view.byteOffset + 20)));
+	const core::vector3df v3(
+		-readFloat(BufferOffset(buffer.data, view.byteOffset + 24)),
+		readFloat(BufferOffset(buffer.data, view.byteOffset + 28)),
+		readFloat(BufferOffset(buffer.data, view.byteOffset + 32)));
+
 	// sorry Bjarne
 	SMeshBuffer* meshbuf { new SMeshBuffer {} };
 
 	const video::S3DVertex* vertices { new video::S3DVertex[3] {
-		{{0.0f, 0.0f, 0.0f}, {0.0f, 0.0f, 1.0f}, {}, {0.0f, 0.0f}},
-		{{0.0f, 1.0f, 0.0f}, {0.0f, 0.0f, 1.0f}, {}, {1.0f, 0.0f}},
-		{{-1.0f, 0.0f, 0.0f}, {0.0f, 0.0f, 1.0f}, {}, {0.0f, 1.0f}} } };
-	const u16* indices { new u16[3] {0, 1, 2} };
+		{v1, {0.0f, 0.0f, 1.0f}, {}, {0.0f, 0.0f}},
+		{v2, {0.0f, 0.0f, 1.0f}, {}, {1.0f, 0.0f}},
+		{v3, {0.0f, 0.0f, 1.0f}, {}, {0.0f, 1.0f}} } };
+	const u16* indices { new u16[3] {0, 2, 1} };
 	meshbuf->append(vertices, 3, indices, 3);
 
 	SMesh* mesh { new SMesh {} };
@@ -57,9 +103,9 @@ IAnimatedMesh* CGLTFMeshFileLoader::createMesh(io::IReadFile* file)
 	return animatedMesh;
 }
 
-bool CGLTFMeshFileLoader::tryParseGLTF(io::IReadFile* file) const
+bool CGLTFMeshFileLoader::tryParseGLTF(io::IReadFile* file,
+		tinygltf::Model& model) const
 {
-	tinygltf::Model model {};
 	tinygltf::TinyGLTF loader {};
 	std::string err {};
 	std::string warn {};
diff --git a/source/Irrlicht/CGLTFMeshFileLoader.h b/source/Irrlicht/CGLTFMeshFileLoader.h
index 46d04d13..766efe67 100644
--- a/source/Irrlicht/CGLTFMeshFileLoader.h
+++ b/source/Irrlicht/CGLTFMeshFileLoader.h
@@ -6,6 +6,8 @@
 #include "IReadFile.h"
 #include "path.h"
 
+#include <tiny_gltf.h>
+
 namespace irr
 {
 
@@ -22,7 +24,7 @@ public:
 	IAnimatedMesh* createMesh(io::IReadFile* file) override;
 
 private:
-	bool tryParseGLTF(io::IReadFile* file) const;
+	bool tryParseGLTF(io::IReadFile* file, tinygltf::Model& model) const;
 };
 
 } // namespace scene
diff --git a/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp b/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp
index c717ac5a..413623e8 100644
--- a/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp
+++ b/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp
@@ -56,8 +56,8 @@ TEST_CASE("minimal triangle has correct vertices") {
 	auto* vertices = reinterpret_cast<irr::video::S3DVertex*>(
 		meshbuf->getVertices());
 	CHECK(vertices[0].Pos == irr::core::vector3df {0.0f, 0.0f, 0.0f});
-	CHECK(vertices[1].Pos == irr::core::vector3df {0.0f, 1.0f, 0.0f});
-	CHECK(vertices[2].Pos == irr::core::vector3df {-1.0f, 0.0f, 0.0f});
+	CHECK(vertices[1].Pos == irr::core::vector3df {-1.0f, 0.0f, 0.0f});
+	CHECK(vertices[2].Pos == irr::core::vector3df {0.0f, 1.0f, 0.0f});
 }
 
 TEST_CASE("mesh loader returns nullptr when given null file pointer") {