psemek/libs/gfx/source/gltf_parser.cpp

#include <psemek/gfx/gltf_parser.hpp>
#include <psemek/util/to_string.hpp>

#include <boost/preprocessor/stringize.hpp>

#define RAPIDJSON_ASSERT(x) if (!(x)) throw ::std::runtime_error("Error parsing glTF: " BOOST_PP_STRINGIZE(x));
#define RAPIDJSON_NOEXCEPT_ASSERT(x)

#include <rapidjson/document.h>
#include <rapidjson/istreamwrapper.h>

namespace psemek::gfx
{

	namespace
	{

		std::string_view to_string(rapidjson::ParseErrorCode const & code)
		{
			using namespace rapidjson;

			switch (code)
			{
			case kParseErrorNone: return "no error";
			case kParseErrorDocumentEmpty: return "document is empty";
			case kParseErrorDocumentRootNotSingular: return "document root must not be followed by other values";
			case kParseErrorValueInvalid: return "invalid value";
			case kParseErrorObjectMissName: return "missing a name for object member";
			case kParseErrorObjectMissColon: return "missing a colon after a name of object member";
			case kParseErrorObjectMissCommaOrCurlyBracket: return "missing a comma or '}' after an object member";
			case kParseErrorArrayMissCommaOrSquareBracket: return "missing a comma or ']' after an array element";
			case kParseErrorStringUnicodeEscapeInvalidHex: return R"(Incorrect hex digit after \\u escape in string)";
			case kParseErrorStringUnicodeSurrogateInvalid: return "surrogate pair in string is invalid";
			case kParseErrorStringEscapeInvalid: return "invalid escape character in string";
			case kParseErrorStringMissQuotationMark: return "missing a closing quotation mark in string";
			case kParseErrorStringInvalidEncoding: return "invalid encoding in string";
			case kParseErrorNumberTooBig: return "number too big to be stored in double";
			case kParseErrorNumberMissFraction: return "missing fraction part in number";
			case kParseErrorNumberMissExponent: return "missing exponent in number";
			case kParseErrorTermination: return "parsing was terminated";
			case kParseErrorUnspecificSyntaxError: return "unspecific syntax error";
			default: return "(unknown error)";
			}
		}

		std::size_t parse_accessor_type(std::string const & type)
		{
			if (type == "SCALAR")
				return 1;
			if (type == "VEC2")
				return 2;
			if (type == "VEC3")
				return 3;
			if (type == "VEC4")
				return 4;
			throw std::runtime_error(util::to_string("Unknown accessor component type: ", type));
		}

	}

	gltf_asset parse_gltf(io::istream && stream)
	{
		auto description_str = io::read_full(std::move(stream));
		description_str.push_back(0);

		rapidjson::Document document;
		document.ParseInsitu(description_str.data());

		if (document.HasParseError())
			throw std::runtime_error(util::to_string("Error parsing glTF: ", to_string(document.GetParseError()), " at ", document.GetErrorOffset()));

		gltf_asset result;

		for (auto const & node : document["nodes"].GetArray())
		{
			auto & target = result.nodes.emplace_back();
			target.mesh = node["mesh"].GetUint64();
			target.name = node["name"].GetString();
		}

		for (auto const & mesh : document["meshes"].GetArray())
		{
			auto & target = result.meshes.emplace_back();
			for (auto const & primitive : mesh["primitives"].GetArray())
			{
				auto & primitive_target = target.primitives.emplace_back();
				primitive_target.indices = primitive["indices"].GetUint64();
				if (primitive.HasMember("material"))
					primitive_target.material = primitive["material"].GetUint64();

				auto const & attributes = primitive["attributes"];
				if (attributes.HasMember("POSITION"))
					primitive_target.position = attributes["POSITION"].GetUint64();
				if (attributes.HasMember("NORMAL"))
					primitive_target.normal = attributes["NORMAL"].GetUint64();
				if (attributes.HasMember("TEXCOORD_0"))
					primitive_target.texcoord = attributes["TEXCOORD_0"].GetUint64();
			}
		}

		for (auto const & material : document["materials"].GetArray())
		{
			auto & target = result.materials.emplace_back();

			auto const & pbr = material["pbrMetallicRoughness"];

			if (pbr.HasMember("baseColorFactor"))
			{
				auto const & color = pbr["baseColorFactor"].GetArray();
				gfx::color_4f & target_color = target.albedo.emplace();
				for (std::size_t i = 0; i < 4; ++i)
					target_color[i] = color[i].GetFloat();
			}

			if (pbr.HasMember("baseColorTexture"))
			{
				target.texture = document["textures"].GetArray()[pbr["baseColorTexture"]["index"].GetUint64()]["source"].GetInt64();
			}
		}

		for (auto const & image : document["images"].GetArray())
		{
			auto & target = result.textures.emplace_back();
			target.uri = image["uri"].GetString();
		}

		for (auto const & accessor : document["accessors"].GetArray())
		{
			auto & target = result.accessors.emplace_back();

			target.buffer_view = accessor["bufferView"].GetUint64();
			target.component_type = accessor["componentType"].GetUint64();
			target.count = accessor["count"].GetUint64();
			target.type = parse_accessor_type(accessor["type"].GetString());

			if (accessor.HasMember("normalized"))
				target.normalized = accessor["normalized"].GetBool();
			else
				target.normalized = false;
		}

		for (auto const & buffer_view : document["bufferViews"].GetArray())
		{
			auto & target = result.buffer_views.emplace_back();

			target.buffer = buffer_view["buffer"].GetUint64();
			target.offset = buffer_view["byteOffset"].GetUint64();
			target.length = buffer_view["byteLength"].GetUint64();
		}

		for (auto const & buffer : document["buffers"].GetArray())
		{
			auto & target = result.buffers.emplace_back();

			target.length = buffer["byteLength"].GetUint64();
			target.uri = buffer["uri"].GetString();
		}

		return result;
	}

}