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#include "obj_parser.hpp"
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <cstddef>
#include <array>
#include <string_view>
#include <optional>
#include "math/vector.hpp"
#include "math/utils.hpp"
#include "o3d/mesh.hpp"
namespace engine {
using math::Vector2, math::Vector3;
template<typename CallbackFn>
static void split(const std::string_view& s, char sep, CallbackFn fn) {
size_t n = 0;
std::string_view::size_type last_ind = 0;
for (std::string_view::size_type ind = 0; ind < s.length(); ind++) {
if (s[ind] == sep) {
if (!fn(n, s.substr(last_ind, ind - last_ind))) return;
n++;
last_ind = ind + 1;
}
}
fn(n, s.substr(last_ind));
}
template<typename NumType>
static std::optional<NumType> parse_num(const std::string_view& s);
template<>
std::optional<float> parse_num<float>(const std::string_view& s) {
std::string::size_type ind = 0;
bool positive = true;
while (ind < s.length() && (s[ind] == '+' || s[ind] == '-'))
if (s[ind++] == '-')
positive = !positive;
if (ind == s.length())
return {};
int n = 0;
while (ind < s.length() && s[ind] >= '0' && s[ind] <= '9')
n = n * 10 + static_cast<int>(s[ind++]) - static_cast<int>('0');
if (ind == s.length())
return (positive ? 1.f : -1.f) * static_cast<float>(n);
if (s[ind] != '.')
return {};
ind++;
float decimal_part = 0.f;
float decimal_fac = .1f;
while (ind < s.length() && s[ind] >= '0' && s[ind] <= '9') {
decimal_part += decimal_fac * static_cast<float>(static_cast<int>(s[ind++]) - static_cast<int>('0'));
decimal_fac *= .1f;
}
if (ind != s.length())
return {};
return (positive ? 1.f : -1.f) * (static_cast<float>(n) + decimal_part);
}
template<>
std::optional<int> parse_num<int>(const std::string_view& s) {
std::string::size_type ind = 0;
bool positive = true;
while (ind < s.length() && (s[ind] == '+' || s[ind] == '-'))
if (s[ind++] == '-')
positive = !positive;
if (ind == s.length())
return {};
int n = 0;
while (ind < s.length() && s[ind] >= '0' && s[ind] <= '9')
n = n * 10 + static_cast<int>(s[ind++]) - static_cast<int>('0');
if (ind != s.length())
return {};
return (positive ? 1.f : -1.f) * n;
}
template<typename VectorType>
static constexpr std::optional<VectorType> split_to_vec(const std::string_view& s, char sep) {
std::array<float, VectorType::size> coords;
bool err = false;
split(s, sep, [&](auto n, const auto& coord_s) {
auto coord = parse_num<float>(coord_s);
if (!coord) {
err = true;
return false;
}
coords[n] = *coord;
return true;
});
if (err) return {};
return engine::math::utils::array_to_vec(coords);
}
// TODO: improve this. This is a workaround to have a unwrap-like function, but we should check more
// precisely the error
template<typename Ret, size_t line_num>
[[noreturn]]
static std::optional<Ret> err_exit() {
std::cerr << "error: failed to parse .obj file (line number " << line_num << ")" << std::endl;
exit(EXIT_FAILURE);
}
o3d::Mesh parse_object(const std::string& obj_path) {
o3d::Mesh mesh;
std::ifstream obj_file(obj_path);
if (!obj_file.is_open()) {
std::cerr << "file `" << obj_path << "' not found" << std::endl; // TODO: improve
exit(EXIT_FAILURE);
}
std::string line;
while (std::getline(obj_file, line)) {
std::string_view line_view { line };
if (line_view.length() == 0 || line_view[0] == '#')
continue;
auto data_type_idx = line_view.find(" ");
if (data_type_idx == std::string_view::npos) {
std::cerr << "error: failed to parse .obj file: no argument given to data type '" << line_view << "`" << std::endl;
exit(EXIT_FAILURE);
}
auto data_type = line_view.substr(0, data_type_idx);
auto data_arg = line_view.substr(data_type_idx + 1);
if (data_type == "o") {
// TODO: implement
} else if (data_type == "v") {
mesh.vertices.push_back(*split_to_vec<Vector3>(data_arg, ' ').or_else(err_exit<Vector3, __LINE__>));
} else if (data_type == "vn") {
mesh.normals.push_back(*split_to_vec<Vector3>(data_arg, ' ').or_else(err_exit<Vector3, __LINE__>));
} else if (data_type == "vt") {
auto uv = *split_to_vec<Vector2>(data_arg, ' ').or_else(err_exit<Vector2, __LINE__>);
uv.y = 1.f - uv.y;
mesh.uvs.push_back(uv);
} else if (data_type == "s") {
// TODO: implement
} else if (data_type == "f") {
std::array<std::array<std::size_t, 3>, 3> indices;
bool err = false;
split(data_arg, ' ', [&](auto m, const auto& vertex_indices_s) {
split(vertex_indices_s, '/', [&](auto n, const auto& idx_s) {
// indices of texture coordinates and normals are reversed in .obj relative to the
// engine
auto idx_opt = parse_num<int>(idx_s);
if (!idx_opt) {
err = true;
return false;
}
indices[m][(n > 0 ? 3 - n : n)] = *idx_opt - 1;
return true;
});
return !err;
});
if (err) err_exit<int, __LINE__>();
mesh.indices.push_back(indices);
} else if (data_type == "mtllib") {
// TODO: implement
} else if (data_type == "usemtl") {
// TODO: implement
} else {
std::cerr << "error while parsing .obj file: unknown data type: " << line_view << std::endl;
exit(EXIT_FAILURE);
}
}
return mesh;
}
}
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