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基于C++的OpenGL 09 之材质

时间：2022-08-14 10:48:15浏览次数：95  
标签：09 glm OpenGL material C++ specular vec3 ambient diffuse

1. 引言

本文基于C++语言，描述OpenGL的材质

前置知识可参考：

笔者这里不过多描述每个名词、函数和细节，更详细的文档可以参考：

2. 概述

不同的物体往往具有不同的材质，不同的材质具有不同的反光特性

在冯氏光照模型中，一个物体的反光由环境光照(Ambient Lighting)、漫反射光照(Diffuse Lighting)和镜面光照(Specular Lighting)组成，通过控制这三个光照因子，可以实现不同材质的光照切换

img

3. 编码

首先在片段着色器中定义影响材质的的三个光照因子，另外，还需要设置一个反光度来表示高光部分的大小

定义材质因子：

#version 330 core
struct Material {
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
    float shininess;
}; 

uniform Material material;

计算材质光照：

void main()
{    
    // 环境光
    vec3 ambient = lightColor * material.ambient;

    // 漫反射 
    vec3 norm = normalize(Normal);
    vec3 lightDir = normalize(lightPos - FragPos);
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = lightColor * (diff * material.diffuse);

    // 镜面光
    vec3 viewDir = normalize(viewPos - FragPos);
    vec3 reflectDir = reflect(-lightDir, norm);  
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
    vec3 specular = lightColor * (spec * material.specular);  

    vec3 result = ambient + diffuse + specular;
    FragColor = vec4(result, 1.0);
}

传输数据至GPU：

lightingShader.setVec3("material.ambient",  1.0f, 0.5f, 0.31f);
lightingShader.setVec3("material.diffuse",  1.0f, 0.5f, 0.31f);
lightingShader.setVec3("material.specular", 0.5f, 0.5f, 0.5f);
lightingShader.setFloat("material.shininess", 32.0f);

结果如下：

image-20220814094936262

结果不太对劲，物体亮度太高，主要是环境光照和漫反射光照太高

接下来将光照因子进行配置，使得环境光照和漫反射光照降低

定义光照因子：

struct Light {
    vec3 position;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

uniform Light light;

计算材质光照：

vec3 ambient  = light.ambient * material.ambient;
vec3 diffuse  = light.diffuse * (diff * material.diffuse);
vec3 specular = light.specular * (spec * material.specular);

传输数据至GPU：

lightingShader.setVec3("light.ambient",  0.2f, 0.2f, 0.2f);
lightingShader.setVec3("light.diffuse",  0.5f, 0.5f, 0.5f); // 将光照调暗了一些以搭配场景
lightingShader.setVec3("light.specular", 1.0f, 1.0f, 1.0f);

结果如下：
image-20220814100328628

设置变化的光照颜色：

glm::vec3 lightColor;
lightColor.x = sin(glfwGetTime() * 2.0f);
lightColor.y = sin(glfwGetTime() * 0.7f);
lightColor.z = sin(glfwGetTime() * 1.3f);

glm::vec3 diffuseColor = lightColor   * glm::vec3(0.5f); // 降低影响
glm::vec3 ambientColor = diffuseColor * glm::vec3(0.2f); // 很低的影响

lightingShader.setVec3("light.ambient", ambientColor);
lightingShader.setVec3("light.diffuse", diffuseColor);

物体随光照颜色变换所展现的颜色变化：

动画2

4. 完整代码

主要文件material.cpp：

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <math.h>
#include "Shader.hpp"
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
#include <glm/glm.hpp>
#include <glm/ext/matrix_transform.hpp>  // glm::translate, glm::rotate, glm::scale
#include <glm/ext/matrix_clip_space.hpp> // glm::perspective
#include <glm/gtc/type_ptr.hpp>

//全局变量
glm::vec3 cameraPos = glm::vec3(0.0f, 0.0f, 10.0f);
glm::vec3 cameraFront = glm::vec3(0.0f, 0.0f, -1.0f);
glm::vec3 cameraUp = glm::vec3(0.0f, 1.0f, 0.0f);
glm::vec3 lightPos(1.2f, 1.0f, 2.0f);

// 函数声明
void framebuffer_size_callback(GLFWwindow *window, int width, int height);
void process_input(GLFWwindow *window);


int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    GLFWwindow *window = glfwCreateWindow(800, 600, "material", nullptr, nullptr);

    if (window == nullptr)
    {
        std::cout << "Faild to create window" << std::endl;
        glfwTerminate();
    }
    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Faild to initialize glad" << std::endl;
        return -1;
    }
    glad_glViewport(0, 0, 800, 600);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    //配置项
    glEnable(GL_DEPTH_TEST);

    Shader lightCubeShader("../light_cube.vs.glsl", "../light_cube.fs.glsl");
    Shader lightingShader("../cube.vs.glsl", "../cube.fs.glsl");

    unsigned int cubeVAO;
    glGenVertexArrays(1, &cubeVAO);
    glBindVertexArray(cubeVAO);

    float vertices[] = {
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
        0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f, 
        0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f, 
        0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f, 
        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f, 
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f, 

        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f, 1.0f,
        0.5f, -0.5f,  0.5f,  0.0f,  0.0f, 1.0f,
        0.5f,  0.5f,  0.5f,  0.0f,  0.0f, 1.0f,
        0.5f,  0.5f,  0.5f,  0.0f,  0.0f, 1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f, 1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f, 1.0f,

        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,
        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,

        0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,
        0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
        0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
        0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
        0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,
        0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,
        0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,
        0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
        0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,

        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
        0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
        0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
        0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f
    };
    unsigned int VBO;
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void *)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void *)(3*sizeof(float)));
    glEnableVertexAttribArray(1);

    unsigned int lightCubeVAO;
    glGenVertexArrays(1, &lightCubeVAO);
    glBindVertexArray(lightCubeVAO);
    // 只需要绑定VBO不用再次设置VBO的数据，因为箱子的VBO数据中已经包含了正确的立方体顶点数据
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    // 设置灯立方体的顶点属性（对我们的灯来说仅仅只有位置数据）
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);


    while (!glfwWindowShouldClose(window))
    {
        process_input(window);

        glClearColor(0.0, 0.0, 0.0, 1.0);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        lightingShader.use();
        lightingShader.setVec3("objectColor", 1.0f, 0.5f, 0.31f);
        lightingShader.setVec3("lightColor", 1.0f, 1.0f, 1.0f);
        lightingShader.setVec3("lightPos", lightPos);
        lightingShader.setVec3("viewPos", cameraPos);
        lightingShader.setVec3("material.ambient",  1.0f, 0.5f, 0.31f);
        lightingShader.setVec3("material.diffuse",  1.0f, 0.5f, 0.31f);
        lightingShader.setVec3("material.specular", 0.5f, 0.5f, 0.5f);
        lightingShader.setFloat("material.shininess", 32.0f);
        // lightingShader.setVec3("light.ambient",  0.2f, 0.2f, 0.2f);
        // lightingShader.setVec3("light.diffuse",  0.5f, 0.5f, 0.5f); // 将光照调暗了一些以搭配场景
        lightingShader.setVec3("light.specular", 1.0f, 1.0f, 1.0f); 
        glm::vec3 lightColor;
        lightColor.x = sin(glfwGetTime() * 2.0f);
        lightColor.y = sin(glfwGetTime() * 0.7f);
        lightColor.z = sin(glfwGetTime() * 1.3f);
        glm::vec3 diffuseColor = lightColor   * glm::vec3(0.5f); // 降低影响
        glm::vec3 ambientColor = diffuseColor * glm::vec3(0.2f); // 很低的影响
        lightingShader.setVec3("light.ambient", ambientColor);
        lightingShader.setVec3("light.diffuse", diffuseColor);
        
        glm::mat4 model = glm::mat4(1.0f);
        model = glm::rotate(model, glm::radians(-55.0f), glm::vec3(1.0f, 0.0f, 0.0f));

        glm::mat4 view = glm::mat4(1.0f);
        // view = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f));
        view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp);

        glm::mat4 projection = glm::mat4(1.0f);
        projection = glm::perspective(glm::radians(45.0f), 800.0f / 600.0f, 0.1f, 100.0f);

        // 模型矩阵
        int modelLoc = glGetUniformLocation(lightingShader.ID, "model");
        glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
        // 观察矩阵和投影矩阵与之类似
        int viewLoc = glGetUniformLocation(lightingShader.ID, "view");
        glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
        int projectionLoc = glGetUniformLocation(lightingShader.ID, "projection");
        glUniformMatrix4fv(projectionLoc, 1, GL_FALSE, glm::value_ptr(projection));

        // render the cube
        glBindVertexArray(cubeVAO);
        glDrawArrays(GL_TRIANGLES, 0, 36);

        // also draw the lamp object
        lightCubeShader.use();
        lightCubeShader.setMat4("projection", projection);
        lightCubeShader.setMat4("view", view);
        model = glm::mat4(1.0f);
        model = glm::translate(model, lightPos);
        model = glm::scale(model, glm::vec3(0.2f)); // a smaller cube
        lightCubeShader.setMat4("model", model);

        glBindVertexArray(lightCubeVAO);
        glDrawArrays(GL_TRIANGLES, 0, 36);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

void framebuffer_size_callback(GLFWwindow *window, int width, int height)
{
    glViewport(0, 0, width, height);
}

void process_input(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
    {
        glfwSetWindowShouldClose(window, true);
    }
    float cameraSpeed = 0.05f; // adjust accordingly
    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        cameraPos += cameraSpeed * cameraFront;
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        cameraPos -= cameraSpeed * cameraFront;
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        cameraPos += glm::normalize(glm::cross(cameraFront, cameraUp)) * cameraSpeed;
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        cameraPos -= glm::normalize(glm::cross(cameraFront, cameraUp)) * cameraSpeed;
}

立方体顶点着色器GLSLcube.vs.glsl：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;

out vec3 Normal;
out vec3 FragPos;  

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{
    gl_Position = projection * view * model * vec4(aPos, 1.0);
    FragPos = vec3(model * vec4(aPos, 1.0));
    Normal = aNormal;
}

立方体片段着色器GLSLcube.fs.glsl：

#version 330 core
struct Material {
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
    float shininess;
}; 
struct Light {
    vec3 position;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

in vec3 Normal;
in vec3 FragPos;

out vec4 FragColor;

uniform vec3 objectColor;
uniform vec3 lightColor;
uniform vec3 lightPos;
uniform vec3 viewPos;
uniform Material material;
uniform Light light;

void main()
{
    // 环境光
    vec3 ambient = light.ambient * material.ambient;

    // 漫反射 
    vec3 norm = normalize(Normal);
    vec3 lightDir = normalize(lightPos - FragPos);
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = light.diffuse * (diff * material.diffuse);

    // 镜面光
    vec3 viewDir = normalize(viewPos - FragPos);
    vec3 reflectDir = reflect(-lightDir, norm);  
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
    vec3 specular = light.specular * (spec * material.specular);  

    vec3 result = ambient + diffuse + specular;
    FragColor = vec4(result, 1.0);
}

着色器Shader.hpp、光源顶点着色器GLSLlight_cube.vs.glsl、光源片段着色器GLSLlight_cube.fs.glsl见：

5. 参考资料

[1]材质 - LearnOpenGL CN (learnopengl-cn.github.io)

标签：09,glm,OpenGL,material,C++,specular,vec3,ambient,diffuse
From： https://www.cnblogs.com/jiujiubashiyi/p/16584920.html

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