From 9c21e2ec1b751d9aa17218b957638ab527329ce9 Mon Sep 17 00:00:00 2001
From: JosiahWI <josiah_vanderzee@mediacombb.net>
Date: Wed, 29 Nov 2023 19:57:58 -0600
Subject: [PATCH] Handle byte stride on vertex buffers

Vertex buffers (and only vertex buffers) may have a byte stride
specified.
---
 source/Irrlicht/CGLTFMeshFileLoader.cpp       | 11 ++-
 source/Irrlicht/CGLTFMeshFileLoader.h         |  2 +
 .../assets/triangle_with_vertex_stride.gltf   | 71 +++++++++++++++++++
 .../tests/testCGLTFMeshFileLoader.cpp         | 12 +++-
 4 files changed, 93 insertions(+), 3 deletions(-)
 create mode 100644 source/Irrlicht/tests/assets/triangle_with_vertex_stride.gltf

diff --git a/source/Irrlicht/CGLTFMeshFileLoader.cpp b/source/Irrlicht/CGLTFMeshFileLoader.cpp
index 59ce3209b..8bec5de26 100644
--- a/source/Irrlicht/CGLTFMeshFileLoader.cpp
+++ b/source/Irrlicht/CGLTFMeshFileLoader.cpp
@@ -224,10 +224,11 @@ void CGLTFMeshFileLoader::MeshExtractor::copyPositions(
 
 	const auto& buffer = getBuffer(accessorIdx);
 	const auto count = getElemCount(accessorIdx);
+	const auto byteStride = getByteStride(accessorIdx);
 
 	for (std::size_t i = 0; i < count; i++) {
 		const auto v = readVec3DF(BufferOffset(buffer,
-			3 * sizeof(float) * i), getScale());
+			(byteStride * i)), getScale());
 		vertices[i].Pos = v;
 	}
 }
@@ -275,6 +276,14 @@ std::size_t CGLTFMeshFileLoader::MeshExtractor::getElemCount(
 	return m_model.accessors[accessorIdx].count;
 }
 
+std::size_t CGLTFMeshFileLoader::MeshExtractor::getByteStride(
+		const std::size_t accessorIdx) const
+{
+	const auto& accessor = m_model.accessors[accessorIdx];
+	const auto& view = m_model.bufferViews[accessor.bufferView];
+	return accessor.ByteStride(view);
+}
+
 CGLTFMeshFileLoader::BufferOffset CGLTFMeshFileLoader::MeshExtractor::getBuffer(
 		const std::size_t accessorIdx) const
 {
diff --git a/source/Irrlicht/CGLTFMeshFileLoader.h b/source/Irrlicht/CGLTFMeshFileLoader.h
index 18f0cc598..2f1411681 100644
--- a/source/Irrlicht/CGLTFMeshFileLoader.h
+++ b/source/Irrlicht/CGLTFMeshFileLoader.h
@@ -104,6 +104,8 @@ private:
 
 		std::size_t getElemCount(const std::size_t accessorIdx) const;
 
+		std::size_t getByteStride(const std::size_t accessorIdx) const;
+
 		BufferOffset getBuffer(const std::size_t accessorIdx) const;
 
 		std::size_t getIndicesAccessorIdx(const std::size_t meshIdx,
diff --git a/source/Irrlicht/tests/assets/triangle_with_vertex_stride.gltf b/source/Irrlicht/tests/assets/triangle_with_vertex_stride.gltf
new file mode 100644
index 000000000..fce122c8a
--- /dev/null
+++ b/source/Irrlicht/tests/assets/triangle_with_vertex_stride.gltf
@@ -0,0 +1,71 @@
+{
+  "scene": 0,
+  "scenes" : [
+    {
+      "nodes" : [ 0 ]
+    }
+  ],
+  
+  "nodes" : [
+    {
+      "mesh" : 0
+    }
+  ],
+  
+  "meshes" : [
+    {
+      "primitives" : [ {
+        "attributes" : {
+          "POSITION" : 1
+        },
+        "indices" : 0
+      } ]
+    }
+  ],
+
+  "buffers" : [
+    {
+      "uri" : "data:application/octet-stream;base64,AAABAAIAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAAAAAAAAAAAA=",
+      "byteLength" : 80
+    }
+  ],
+  "bufferViews" : [
+    {
+      "buffer" : 0,
+      "byteOffset" : 0,
+      "byteLength" : 6,
+      "target" : 34963
+    },
+    {
+      "buffer" : 0,
+      "byteOffset" : 8,
+      "byteLength" : 36,
+      "byteStride" : 24,
+      "target" : 34962
+    }
+  ],
+  "accessors" : [
+    {
+      "bufferView" : 0,
+      "byteOffset" : 0,
+      "componentType" : 5123,
+      "count" : 3,
+      "type" : "SCALAR",
+      "max" : [ 2 ],
+      "min" : [ 0 ]
+    },
+    {
+      "bufferView" : 1,
+      "byteOffset" : 0,
+      "componentType" : 5126,
+      "count" : 3,
+      "type" : "VEC3",
+      "max" : [ 1.0, 1.0, 0.0 ],
+      "min" : [ 0.0, 0.0, 0.0 ]
+    }
+  ],
+  
+  "asset" : {
+    "version" : "2.0"
+  }
+}
diff --git a/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp b/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp
index 86d7ff09d..ea75c738c 100644
--- a/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp
+++ b/source/Irrlicht/tests/testCGLTFMeshFileLoader.cpp
@@ -1,8 +1,12 @@
 #include "CReadFile.h"
 
+#include <irrlicht.h>
+
+// Catch needs to be included after Irrlicht so that it sees operator<<
+// declarations.
 #define CATCH_CONFIG_MAIN
 #include <catch.hpp>
-#include <irrlicht.h>
+
 #include <iostream>
 
 using namespace std;
@@ -49,7 +53,11 @@ TEST_CASE("load empty gltf file") {
 }
 
 TEST_CASE("minimal triangle") {
-	ScopedMesh sm("source/Irrlicht/tests/assets/minimal_triangle.gltf");
+	auto path = GENERATE(
+		"source/Irrlicht/tests/assets/minimal_triangle.gltf",
+		"source/Irrlicht/tests/assets/triangle_with_vertex_stride.gltf");
+	INFO(path);
+	ScopedMesh sm(path);
 	REQUIRE(sm.getMesh() != nullptr);
 	REQUIRE(sm.getMesh()->getMeshBufferCount() == 1);