mesh.h

#pragma once
#ifndef MESH_H
#define MESH_H

#include <glad/glad.h> // holds all OpenGL type declarations

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include "shader.h"

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <vector>
using namespace std;

struct Vertex {
	// position
	glm::vec3 Position;//顶点位置
	// normal
	glm::vec3 Normal;//法向量
	// texCoords
	glm::vec2 TexCoords;//纹理坐标
	// tangent
	glm::vec3 Tangent;
	// bitangent
	glm::vec3 Bitangent;
};

struct Texture {
	unsigned int id;//纹理ID（序号）
	string type;//纹理类型（漫反射贴图 or 镜面光贴图）
	string path;
};

class Mesh {
public:
	/*  Mesh Data  */
	// 网格数据
	vector<Vertex> vertices;//装有所有数据向量
	vector<unsigned int> indices;//所有索引数据
	vector<Texture> textures;//纹理属性
	unsigned int VAO;

	/*  Functions  */
	// constructor
	// 传入数据
	Mesh(vector<Vertex> vertices, vector<unsigned int> indices, vector<Texture> textures)
	{
		this->vertices = vertices;
		this->indices = indices;
		this->textures = textures;

		// now that we have all the required data, set the vertex buffers and its attribute pointers.
		// 初始化缓冲
		setupMesh();
	}

	// render the mesh
	// 最终使用Draw函数来绘制网格
	void Draw(Shader shader)
	{
		// bind appropriate textures
		// 设置uniform
		// 链接采样器到纹理单元
		unsigned int diffuseNr = 1;
		unsigned int specularNr = 1;
		unsigned int normalNr = 1;
		unsigned int heightNr = 1;
		for (unsigned int i = 0; i < textures.size(); i++)
		{
			//在绑定之前先激活相应的纹理单元
			glActiveTexture(GL_TEXTURE0 + i); // active proper texture unit before binding
											  // retrieve texture number (the N in diffuse_textureN)
			//获取纹理序号（diffuse_textureN 中的 N）
			string number;
			string name = textures[i].type;
			if (name == "texture_diffuse")
				number = std::to_string(diffuseNr++);
			else if (name == "texture_specular")
				number = std::to_string(specularNr++); // transfer unsigned int to stream
			else if (name == "texture_normal")
				number = std::to_string(normalNr++); // transfer unsigned int to stream
			else if (name == "texture_height")
				number = std::to_string(heightNr++); // transfer unsigned int to stream

													 // now set the sampler to the correct texture unit
			// glGetUniformLocation查询uniform变量地址，然后指定每个着色器采样器属于哪个纹理单元
			glUniform1i(glGetUniformLocation(shader.ID, (name + number).c_str()), i);
			// and finally bind the texture
			// 绑定纹理
			glBindTexture(GL_TEXTURE_2D, textures[i].id);
		}

		// draw mesh
		glBindVertexArray(VAO);
		glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, 0);
		glBindVertexArray(0);

		// always good practice to set everything back to defaults once configured.
		glActiveTexture(GL_TEXTURE0);

	}

private:
	/*  Render data  */
	//渲染数据
	unsigned int VBO, EBO;

	/*  Functions    */
	// initializes all the buffer objects/arrays
	// 在setupMesh函数中初始化缓冲
	void setupMesh()
	{
		// create buffers/arrays
		glGenVertexArrays(1, &VAO);
		glGenBuffers(1, &VBO);
		glGenBuffers(1, &EBO);

		glBindVertexArray(VAO);
		// load data into vertex buffers
		glBindBuffer(GL_ARRAY_BUFFER, VBO);
		// A great thing about structs is that their memory layout is sequential for all its items.
		// The effect is that we can simply pass a pointer to the struct and it translates perfectly to a glm::vec3/2 array which
		// again translates to 3/2 floats which translates to a byte array.
		glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(Vertex), &vertices[0], GL_STATIC_DRAW);

		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned int), &indices[0], GL_STATIC_DRAW);

		// set the vertex attribute pointers
		// 通过定点属性指针定义顶点着色器的布局
		// vertex Positions
		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)0);
		// vertex normals
		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Normal));
		// vertex texture coords
		glEnableVertexAttribArray(2);
		glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, TexCoords));
		// vertex tangent
		glEnableVertexAttribArray(3);
		glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Tangent));
		// vertex bitangent
		glEnableVertexAttribArray(4);
		glVertexAttribPointer(4, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Bitangent));

		glBindVertexArray(0);
	}
};
#endif