基于C++的OpenGL 08 之基础光照
本文基于C++语言，描述OpenGL的基础光照
1. 引言
本文基于C++语言，描述OpenGL的基础光照
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
冯氏光照模型(Phong Lighting Model)：环境(Ambient)、漫反射(Diffuse)和镜面(Specular)光照
漫反射光照的强度由法向量与光的方向向量的余弦值决定，角度越小，光照越强
镜面光照的强度由视线向量与光的反射向量的余弦值决定，角度越小，光照越强
3. 环境光照
使用一个很小的常量因子乘以光的颜色，模拟环境光照
在片段着色器GLSL中：
...
void main()
{
float ambientStrength = 0.1;
vec3 ambient = ambientStrength * lightColor;
vec3 result = ambient * objectColor;
FragColor = vec4(result, 1.0);
}
结果如下图：
4. 漫反射光照
使用光线与法向量的余弦值作为漫反射因子，再乘以光的颜色来模拟漫反射光照
在这里，法向量由我们手动输入，光的方向由光的位置向量减去平面的位置向量获取
4.1 法向量
设置物体每个平面的法向量：
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
};
绑定属性：
// 立方体
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);
// 光源立方体
...
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
在顶点着色器中将法向量变换为世界坐标并向片段着色器传递数据：
#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;
...
out vec3 Normal;
void main()
{
gl_Position = projection * view * model * vec4(aPos, 1.0);
Normal = mat3(transpose(inverse(model))) * aNormal;
}
在片段着色器接收数据：
in vec3 Normal;
void main()
{
...
vec3 norm = normalize(Normal);
}
4.2 光的方向向量
在片段着色器中设置光源位置向量：
uniform vec3 lightPos;
传输数据：
lightingShader.setVec3("lightPos", lightPos);
将平面位置变换到世界坐标得到位置向量：
out vec3 FragPos;
out vec3 Normal;
void main()
{
gl_Position = projection * view * model * vec4(aPos, 1.0);
FragPos = vec3(model * vec4(aPos, 1.0));
Normal = aNormal;
}
在片段着色器接收数据并计算光的方向向量：
...
in vec3 FragPos;
void main()
{
...
vec3 lightDir = normalize(lightPos - FragPos);
}
4.3 计算漫反射光照
计算方向向量与光的方向向量之间的余弦值作为漫反射因子（小于零的设为零），再乘以光照颜色得到漫反射光照
在片段着色器中：
float diff = max(dot(norm, lightDir), 0.0);
vec3 diffuse = diff * lightColor;
将环境光照与漫反射光照结合：
vec3 result = (ambient + diffuse) * objectColor;
FragColor = vec4(result, 1.0);
结果如下图：
5. 镜面光照
计算视线向量与光的反射向量之间的余弦值作为镜面反射因子（小于零的设为零），再乘以光照颜色得到漫反射光照
在片段着色器中设置观察位置：
uniform vec3 viewPos;
向GPU传输数据：
lightingShader.setVec3("viewPos", cameraPos);
计算视线向量（观察方向）与反射向量：
vec3 viewDir = normalize(viewPos - FragPos);
vec3 reflectDir = reflect(-lightDir, norm);
定义镜面强度，即反射能力：
float specularStrength = 0.5;
计算镜面光照：
float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);
vec3 specular = specularStrength * spec * lightColor;
将环境光照、漫反射光照、镜面光照结合：
vec3 result = (ambient + diffuse + specular) * objectColor;
FragColor = vec4(result, 1.0);
结果如下图：
6. 完整代码
主要文件Lighting.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, "lighting", 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);
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GLSLcue.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
in vec3 Normal;
in vec3 FragPos;
out vec4 FragColor;
uniform vec3 objectColor;
uniform vec3 lightColor;
uniform vec3 lightPos;
uniform vec3 viewPos;
void main()
{
float ambientStrength = 0.1;
vec3 ambient = ambientStrength * lightColor;
vec3 norm = normalize(Normal);
vec3 lightDir = normalize(lightPos - FragPos);
float diff = max(dot(norm, lightDir), 0.0);
vec3 diffuse = diff * lightColor;
vec3 viewDir = normalize(viewPos - FragPos);
vec3 reflectDir = reflect(-lightDir, norm);
float specularStrength = 0.8;
float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);
vec3 specular = specularStrength * spec * lightColor;
vec3 result = (ambient + diffuse + specular) * objectColor;
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：
