utad-3d/src/mesh.cpp

#include "mesh.h"

#include <filesystem>
#include <string>
#include <unordered_map>

#include "../lib/tiny_obj_loader.h"

#include "buffer.h"
#include "logger.h"
#include "material.h"
#include "shader.h"
#include "state.h"
#include "texture.h"
#include "vertex.h"

// Helper structures and functions for OBJ loading
namespace {

struct LoadContext {
	std::string						  base_dir;
	std::unordered_map<std::string, std::shared_ptr<Texture>> texture_cache;
	const std::vector<tinyobj::material_t>*			  materials;
	const std::shared_ptr<Shader>&				  shader;
};

Vertex create_vertex(const tinyobj::attrib_t& attrib,
		     const tinyobj::index_t&  idx)
{
	Vertex vertex;

	// Position
	if (idx.vertex_index >= 0) {
		vertex.position.x = attrib.vertices[3 * idx.vertex_index + 0];
		vertex.position.y = attrib.vertices[3 * idx.vertex_index + 1];
		vertex.position.z = attrib.vertices[3 * idx.vertex_index + 2];
	}

	// Color (default to white)
	vertex.color = glm::vec3(1.0f, 1.0f, 1.0f);

	// Texture coordinates
	vertex.tex_coord = glm::vec2(0.0f, 0.0f);
	if (idx.texcoord_index >= 0) {
		vertex.tex_coord.x = attrib.texcoords[2 * idx.texcoord_index + 0];
		vertex.tex_coord.y = attrib.texcoords[2 * idx.texcoord_index + 1];
	}

	return vertex;
}

void process_shape(const tinyobj::shape_t&   shape,
		   const tinyobj::attrib_t& attrib,
		   std::vector<Vertex>&	    out_vertices,
		   std::vector<uint16_t>&   out_indices)
{
	// Process all indices - create one vertex per index
	for (size_t i = 0; i < shape.mesh.indices.size(); ++i) {
		const tinyobj::index_t& idx = shape.mesh.indices[i];
		Vertex			vertex	= create_vertex(attrib, idx);

		out_vertices.push_back(vertex);
		out_indices.push_back(
		    static_cast<uint16_t>(out_vertices.size() - 1));
	}
}

std::shared_ptr<Texture> load_material_texture(int	    material_id,
					       LoadContext& context)
{
	if (material_id < 0
	    || material_id >= static_cast<int>(context.materials->size())) {
		return nullptr;
	}

	const auto& mat		 = (*context.materials)[material_id];
	std::string texture_name = mat.diffuse_texname;

	// Try ambient texture if diffuse is not available
	if (texture_name.empty()) {
		texture_name = mat.ambient_texname;
	}

	if (texture_name.empty()) {
		return nullptr;
	}

	// Check cache first
	auto it = context.texture_cache.find(texture_name);
	if (it != context.texture_cache.end()) {
		return it->second;
	}

	// Load texture
	std::string texture_path = context.base_dir + texture_name;
	auto	    texture	 = Texture::load(texture_path.c_str());

	if (texture) {
		context.texture_cache[texture_name] = texture;
		Logger::info(sstr("Loaded texture: ", texture_path));
	} else {
		Logger::warn(sstr("Failed to load texture: ", texture_path));
	}

	return texture;
}

void create_buffer_for_shape(const tinyobj::shape_t&   shape,
			     const std::vector<Vertex>&	   vertices,
			     const std::vector<uint16_t>& indices,
			     LoadContext&		   context,
			     std::shared_ptr<Mesh>&	   mesh)
{
	auto buffer = std::make_shared<Buffer>(vertices, indices);

	// Use first material ID from the shape
	int material_id = -1;
	if (!shape.mesh.material_ids.empty() && shape.mesh.material_ids[0] >= 0) {
		material_id = shape.mesh.material_ids[0];
	}

	auto texture = load_material_texture(material_id, context);
	auto material_shader =
	    context.shader ? context.shader : state::default_shader;

	Material mat(texture, material_shader);
	mesh->add_buffer(buffer, mat);
}

} // namespace

void Mesh::add_buffer(const std::shared_ptr<Buffer>& buffer,
		      const Material&		     material)
{
	buffers_.push_back(buffer);
	materials_.push_back(material);
}

std::shared_ptr<Mesh> Mesh::load(const char*			filename,
				 const std::shared_ptr<Shader>& shader)
{
	Logger::info(sstr("Loading mesh from: ", filename));

	// Load OBJ file
	tinyobj::attrib_t		 attrib;
	std::vector<tinyobj::shape_t>	 shapes;
	std::vector<tinyobj::material_t> materials;
	std::string			 err;

	std::filesystem::path obj_path(filename);
	std::string	      base_dir = obj_path.parent_path().string();
	if (!base_dir.empty()) {
		base_dir += "/";
	}

	if (!tinyobj::LoadObj(&attrib, &shapes, &materials, &err, filename,
			      base_dir.c_str())) {
		Logger::error(
		    sstr("Failed to load OBJ file: ", filename, " - ", err));
		return nullptr;
	}

	if (!err.empty()) {
		Logger::warn(sstr("TinyObjLoader warning: ", err));
	}

	// Setup load context
	LoadContext context{base_dir, {}, &materials, shader};

	// Process each shape
	auto mesh = std::make_shared<Mesh>();
	for (const auto& shape : shapes) {
		Logger::info(sstr("Processing shape: ", shape.name));

		std::vector<Vertex>   vertices;
		std::vector<uint16_t> indices;

		process_shape(shape, attrib, vertices, indices);
		create_buffer_for_shape(shape, vertices, indices, context, mesh);
	}

	Logger::info(sstr("Mesh loaded successfully with ", mesh->num_buffers(),
			  " buffers"));
	return mesh;
}

void Mesh::draw()
{
	// Draw each buffer with its material
	for (size_t i = 0; i < buffers_.size(); ++i) {
		materials_[i].prepare();
		buffers_[i]->draw(*materials_[i].shader());
	}
}