From c3d964fafd0776f7f11dedaf9c455633973a6c26 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Wed, 3 Jan 2024 02:21:16 +0300
Subject: [PATCH] Support loading GLB assets

---
 libs/gfx/include/psemek/gfx/gltf_parser.hpp |  3 ++
 libs/gfx/source/gltf_parser.cpp             | 55 ++++++++++++++++++++-
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/libs/gfx/include/psemek/gfx/gltf_parser.hpp b/libs/gfx/include/psemek/gfx/gltf_parser.hpp
index b0980230..7c52cdbf 100644
--- a/libs/gfx/include/psemek/gfx/gltf_parser.hpp
+++ b/libs/gfx/include/psemek/gfx/gltf_parser.hpp
@@ -140,6 +140,8 @@ namespace psemek::gfx
 		{
 			std::size_t length;
 			std::string uri;
+
+			std::optional<util::blob> data; // for GLB buffer
 		};
 
 		// KHR_lights_punctual
@@ -184,6 +186,7 @@ namespace psemek::gfx
 	};
 
 	gltf_asset parse_gltf(io::istream && stream);
+	gltf_asset parse_glb(io::istream && stream);
 
 	std::size_t attribute_size(gltf_asset::accessor::type_t type);
 
diff --git a/libs/gfx/source/gltf_parser.cpp b/libs/gfx/source/gltf_parser.cpp
index e31491a0..d4083d55 100644
--- a/libs/gfx/source/gltf_parser.cpp
+++ b/libs/gfx/source/gltf_parser.cpp
@@ -4,6 +4,7 @@
 #include <psemek/geom/translation.hpp>
 #include <psemek/util/to_string.hpp>
 #include <psemek/util/exception.hpp>
+#include <psemek/io/memory_stream.hpp>
 #include <psemek/log/log.hpp>
 
 #include <boost/preprocessor/stringize.hpp>
@@ -378,7 +379,9 @@ namespace psemek::gfx
 			auto & target = result.buffers.emplace_back();
 
 			target.length = buffer["byteLength"].GetUint64();
-			target.uri = buffer["uri"].GetString();
+
+			if (buffer.HasMember("uri"))
+				target.uri = buffer["uri"].GetString();
 		}
 
 		if (document.HasMember("extensions")) for (auto const & extension : document["extensions"].GetObject())
@@ -451,6 +454,56 @@ namespace psemek::gfx
 		return result;
 	}
 
+	gltf_asset parse_glb(io::istream && stream)
+	{
+		std::uint32_t magic, version, length;
+		stream.read_all((char *)&magic, 4);
+		stream.read_all((char *)&version, 4);
+		stream.read_all((char *)&length, 4);
+
+		if (magic != 0x46546c67u)
+			throw std::runtime_error("Error parsing GLB magic");
+
+		if (version != 2)
+			throw std::runtime_error("Unknown GLB file version");
+
+		length -= 12;
+
+		gltf_asset result;
+
+		while (length > 0)
+		{
+			std::uint32_t chunk_length, chunk_type;
+			stream.read_all((char *)&chunk_length, 4);
+			stream.read_all((char *)&chunk_type, 4);
+
+			util::blob data(chunk_length);
+			stream.read_all(data.data(), chunk_length);
+
+			length -= 8;
+			length -= chunk_length;
+
+			if (chunk_type == 0x4e4f534au)
+			{
+				result = parse_gltf(io::memory_istream(data.begin(), data.end()));
+			}
+			else if (chunk_type == 0x004e4942u)
+			{
+				if (result.buffers.empty())
+					throw std::runtime_error("Error parsing GLB: glTF chunk has no buffers");
+
+				if (!result.buffers[0].uri.empty())
+					throw std::runtime_error("Error parsing GLB: first glTF buffer has URI");
+
+				result.buffers[0].data = std::move(data);
+			}
+			else
+				throw std::runtime_error("Error parsing GLB: unknown chunk type");
+		}
+
+		return result;
+	}
+
 	std::size_t attribute_size(gltf_asset::accessor::type_t type)
 	{
 		using type_t = gltf_asset::accessor::type_t;