Использование нескольких диффузных и бликовых текстур openGL

В уроке по openGL сказано, что для полигональной сетки может одновременно использоваться несколько бликовых и диффузных текстур, но как это реализовать в шейдер я не знаю. Объясните как будут вести себя несколько однотипных текстур, желательно с примером кода шейдера.

Код фрагментного шейдера:

#version 330 core
out vec4 FragColor;

struct Material
{
    sampler2D diffuse;
    sampler2D specular;
    float shininess;
};

struct DirLight
{
    vec3 direction;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

struct PointLight
{
    vec3  position;

    float constant;
    float linear;
    float quadratic;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

struct SpotLight
{
    vec3 position;
    vec3 direction;
    float cutOff;
    float outerCutOff;

    float constant;
    float linear;
    float quadratic;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

#define NR_POINT_LIGHTS 4

in vec3 Normal;
in vec3 FragPos;
in vec2 TexCoords;

uniform vec3 viewPos;
uniform Material material;
uniform DirLight dirLight;
uniform PointLight pointLights[NR_POINT_LIGHTS];
uniform SpotLight spotLight;

vec3 CalcDirLight(DirLight light, vec3 normal, vec3 viewDir);
vec3 CalcPointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir);
vec3 CalcSpotLight(SpotLight light, vec3 normal, vec3 fragPos, vec3 viewDir);

void main()
{
    vec3 norm = normalize(Normal);
    vec3 viewDir = normalize(viewPos - FragPos);

    vec3 result;

    result = CalcDirLight(dirLight, norm, viewDir);

    for(int i = 0; i < NR_POINT_LIGHTS; i++)
        result += CalcPointLight(pointLights[i], norm, FragPos, viewDir);

    result += CalcSpotLight(spotLight, norm, FragPos, viewDir);    
    
    FragColor = vec4(result, 1.0);
}

vec3 CalcDirLight(DirLight light, vec3 normal, vec3 viewDir)
{
    vec3 lightDir = normalize(-light.direction);

    float diff = max(dot(normal, lightDir), 0.0);
    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);

    vec3 ambient  = light.ambient  * vec3(texture(material.diffuse, TexCoords));
    vec3 diffuse  = light.diffuse  * diff * vec3(texture(material.diffuse, TexCoords));
    vec3 specular = light.specular * spec * vec3(texture(material.specular, TexCoords));
    return (ambient + diffuse + specular);
}

vec3 CalcPointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
    vec3 lightDir = normalize(light.position - fragPos);

    float diff = max(dot(normal, lightDir), 0.0);

    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);

    float distance    = length(light.position - fragPos);
    float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));

    vec3 ambient  = light.ambient  * vec3(texture(material.diffuse, TexCoords));
    vec3 diffuse  = light.diffuse  * diff * vec3(texture(material.diffuse, TexCoords));
    vec3 specular = light.specular * spec * vec3(texture(material.specular, TexCoords));
    ambient  *= attenuation;
    diffuse  *= attenuation;
    specular *= attenuation;
    return (ambient + diffuse + specular);
}

vec3 CalcSpotLight(SpotLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
    vec3 lightDir = normalize(light.position - fragPos);

    float diff = max(dot(normal, lightDir), 0.0);

    vec3 reflectDir = reflect(-lightDir, normal);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);

    float distance = length(light.position - fragPos);
    float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));

    float theta = dot(lightDir, normalize(-light.direction)); 
    float epsilon = light.cutOff - light.outerCutOff;
    float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);

    vec3 ambient = light.ambient * vec3(texture(material.diffuse, TexCoords));
    vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, TexCoords));
    vec3 specular = light.specular * spec * vec3(texture(material.specular, TexCoords));
    ambient *= attenuation * intensity;
    diffuse *= attenuation * intensity;
    specular *= attenuation * intensity;
    return (ambient + diffuse + specular);
}

Код класса полигональной сетки Mesh.cpp:

#include "Mesh.h"

Mesh::Mesh(std::vector<Vertex> vertices, std::vector<unsigned int> indices, std::vector<Texture> textures)
{
    this->vertices = vertices;
    this->indices = indices;
    this->textures = textures;

    setupMesh();
}

void Mesh::setupMesh()
{
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);

    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);

    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);

    // 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));

    glBindVertexArray(0);
}

void Mesh::Draw(Shader shader)
{
    for (unsigned int i = 0; i < textures.size(); i++)
    {
        glActiveTexture(GL_TEXTURE0 + i);

        //Как правильно передать текстуры в шейдер???
        glBindTexture(GL_TEXTURE_2D, textures[i].id);
    }
    glActiveTexture(GL_TEXTURE0);

    glBindVertexArray(VAO);
    glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, 0);
    glBindVertexArray(0);
}

Должно получиться что-то такое: