1. 引言
本文基于C++语言，描述OpenGL的投光物
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
投光物，即光源，主要有平行光源、点光源和聚光源
平行光源可以使用一个方向向量来模拟
点光源可以使用一个点来模拟，另外，点光源应该有衰减模拟，衰减公式为
\[\begin{equation} F_{att} = \frac{1.0}{K_c + K_l * d + K_q * d^2} \end{equation} \]- 常数项通常保持为1.0，它的主要作用是保证分母永远不会比1小，否则的话在某些距离上它反而会增加强度
- 一次项会与距离值相乘，以线性的方式减少强度
- 二次项会与距离的平方相乘，让光源以二次递减的方式减少强度
\(K_l\)与\(K_q\)的取值可以参考实验值：-Point Light Attenuation | Ogre Wiki (ogre3d.org)
聚光源类似于手电筒、聚光灯，只照亮灯光方向的一部分，如下图所示
图中，参数含义如下：
LightDir：从片段指向光源的向量SpotDir：聚光所指向的方向Phi\(\phi\)：指定了聚光半径的切光角。落在这个角度之外的物体都不会被这个聚光所照亮Theta\(\theta\)：LightDir向量和SpotDir向量之间的夹角。在聚光内部的话θ值应该比ϕ值小
计算LightDir向量和SpotDir向量之间的点积得到两个单位向量夹角的余弦值，并将它与切光角ϕ值对比，即可判断是否被照亮
3. 编码
3.1 平行光
使用一个光线方向向量来模拟平行光
在片段着色器中定义光线的方向向量：
struct Light {
// vec3 position; // 使用定向光就不再需要了
vec3 direction;
vec3 ambient;
vec3 diffuse;
vec3 specular;
};
...
void main()
{
vec3 lightDir = normalize(-light.direction);
...
}
输入方向向量：
lightingShader.setVec3("light.direction", -1.0f, 0.0f, 0.0f);
结果如下：
3.2 点光源
给定一个点位置来模拟点光源，并且设置衰减的参数
这里\(K_l\)与\(K_q\)的取值使用的是50米光源的实验值，分别0.09、0.032
在片段着色器中定义参数：
struct Light {
vec3 position;
vec3 ambient;
vec3 diffuse;
vec3 specular;
float constant;
float linear;
float quadratic;
};
计算衰减：
float distance = length(light.position - FragPos);
float attenuation = 1.0 / (light.constant + light.linear * distance +
light.quadratic * (distance * distance));
ambient *= attenuation;
diffuse *= attenuation;
specular *= attenuation;
想GPU输入数据：
lightingShader.setFloat("light.constant", 1.0f);
lightingShader.setFloat("light.linear", 0.09f);
lightingShader.setFloat("light.quadratic", 0.032f);
实现效果如下：
3.3 聚光源
在片段着色器中定义聚光源的参数：
struct Light {
vec3 position;
vec3 direction;
float cutOff;
...
};
计算是否照亮：
float theta = dot(lightDir, normalize(-light.direction));
if(theta > light.cutOff)
{
// 执行光照计算
}
else // 否则，使用环境光，让场景在聚光之外时不至于完全黑暗
color = vec4(light.ambient * vec3(texture(material.diffuse, TexCoords)), 1.0);
向GPU传输数据：
lightingShader.setVec3("light.position", cameraPos);
lightingShader.setVec3("light.direction", cameraFront);
lightingShader.setFloat("light.cutOff", glm::cos(glm::radians(35.0f)));
结果如下：
目前看起来边缘过渡，使用一个外半径进行边缘过渡是必要的
计算公式为：
\[\begin{equation} I = \frac{\theta - \gamma}{\epsilon} \end{equation} \]这里\(\epsilon\)(Epsilon)是内（\(\theta\)）和外圆锥（\(\gamma\)）之间的余弦值差（\(\epsilon = \phi - \gamma\)），最终的\(I\)值就是在当前片段聚光的强度
在片段着色器中定义参数：
struct Light {
float outerCutOff;
...
};
...
void main()
{
....
float theta = dot(lightDir, normalize(-light.direction));
float epsilon = light.cutOff - light.outerCutOff;
float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);
...
// 将不对环境光做出影响，让它总是能有一点光
diffuse *= intensity;
specular *= intensity;
...
}
输入数据：
lightingShader.setFloat("light.outerCutOff", glm::cos(glm::radians(40.0f)));
实现效果如下：
4. 完整代码
主要文件caster.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(0.8f, 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, "caster", 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[] = {
// positions // normals // texture coords
-0.5f, -0.5f, -0.5f, 0.0f, 0.0f, -1.0f, 0.0f, 0.0f,
0.5f, -0.5f, -0.5f, 0.0f, 0.0f, -1.0f, 1.0f, 0.0f,
0.5f, 0.5f, -0.5f, 0.0f, 0.0f, -1.0f, 1.0f, 1.0f,
0.5f, 0.5f, -0.5f, 0.0f, 0.0f, -1.0f, 1.0f, 1.0f,
-0.5f, 0.5f, -0.5f, 0.0f, 0.0f, -1.0f, 0.0f, 1.0f,
-0.5f, -0.5f, -0.5f, 0.0f, 0.0f, -1.0f, 0.0f, 0.0f,
-0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,
0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f,
0.5f, 0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f,
0.5f, 0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f,
-0.5f, 0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f,
-0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,
-0.5f, 0.5f, 0.5f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f,
-0.5f, 0.5f, -0.5f, -1.0f, 0.0f, 0.0f, 1.0f, 1.0f,
-0.5f, -0.5f, -0.5f, -1.0f, 0.0f, 0.0f, 0.0f, 1.0f,
-0.5f, -0.5f, -0.5f, -1.0f, 0.0f, 0.0f, 0.0f, 1.0f,
-0.5f, -0.5f, 0.5f, -1.0f, 0.0f, 0.0f, 0.0f, 0.0f,
-0.5f, 0.5f, 0.5f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f,
0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f,
0.5f, 0.5f, -0.5f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f,
0.5f, -0.5f, -0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f,
0.5f, -0.5f, -0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f,
0.5f, -0.5f, 0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f,
0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f,
-0.5f, -0.5f, -0.5f, 0.0f, -1.0f, 0.0f, 0.0f, 1.0f,
0.5f, -0.5f, -0.5f, 0.0f, -1.0f, 0.0f, 1.0f, 1.0f,
0.5f, -0.5f, 0.5f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f,
0.5f, -0.5f, 0.5f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f,
-0.5f, -0.5f, 0.5f, 0.0f, -1.0f, 0.0f, 0.0f, 0.0f,
-0.5f, -0.5f, -0.5f, 0.0f, -1.0f, 0.0f, 0.0f, 1.0f,
-0.5f, 0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f,
0.5f, 0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f,
0.5f, 0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f,
0.5f, 0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f,
-0.5f, 0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f,
-0.5f, 0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f
};
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, 8 * sizeof(float), (void *)0);
glEnableVertexAttribArray(0);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void *)(3*sizeof(float)));
glEnableVertexAttribArray(1);
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void *)(6*sizeof(float)));
glEnableVertexAttribArray(2);
// 纹理
unsigned int texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
// 为当前绑定的纹理对象设置环绕、过滤方式
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// 加载并生成纹理
int width, height, nrChannels;
unsigned char *data = stbi_load("../container2.png", &width, &height, &nrChannels, 0);
if (data)
{
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
glGenerateMipmap(GL_TEXTURE_2D);
}
else
{
std::cout << "Failed to load texture" << std::endl;
}
stbi_image_free(data);
lightingShader.setInt("material.diffuse", 0);
// 镜面反射纹理
unsigned int texture1;
glGenTextures(1, &texture1);
glBindTexture(GL_TEXTURE_2D, texture1);
// 为当前绑定的纹理对象设置环绕、过滤方式
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// 加载并生成纹理
data = stbi_load("../container2_specular.png", &width, &height, &nrChannels, 0);
if (data)
{
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
glGenerateMipmap(GL_TEXTURE_2D);
}
else
{
std::cout << "Failed to load texture" << std::endl;
}
stbi_image_free(data);
lightingShader.setInt("material.diffuse", 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, 8 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// positions all containers
glm::vec3 cubePositions[] = {
glm::vec3( 0.0f, 0.0f, 0.0f),
glm::vec3( 2.0f, 5.0f, -15.0f),
glm::vec3(-1.5f, -2.2f, -2.5f),
glm::vec3(-3.8f, -2.0f, -12.3f),
glm::vec3( 2.4f, -0.4f, -3.5f),
glm::vec3(-1.7f, 3.0f, -7.5f),
glm::vec3( 1.3f, -2.0f, -2.5f),
glm::vec3( 1.5f, 2.0f, -2.5f),
glm::vec3( 1.5f, 0.2f, -1.5f),
glm::vec3(-1.3f, 1.0f, -1.5f)
};
while (!glfwWindowShouldClose(window))
{
process_input(window);
glClearColor(0.0, 0.0, 0.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, texture1);
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.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);
// lightingShader.setVec3("light.direction", -1.0f, 0.0f, 0.0f);
// lightingShader.setFloat("light.constant", 1.0f);
// lightingShader.setFloat("light.linear", 0.09f);
// lightingShader.setFloat("light.quadratic", 0.032f);
lightingShader.setVec3("light.position", cameraPos);
lightingShader.setVec3("light.direction", cameraFront);
lightingShader.setFloat("light.cutOff", glm::cos(glm::radians(35.0f)));
lightingShader.setFloat("light.outerCutOff", glm::cos(glm::radians(40.0f)));
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);
for (unsigned int i = 0; i < 10; i++)
{
// calculate the model matrix for each object and pass it to shader before drawing
glm::mat4 model = glm::mat4(1.0f);
model = glm::translate(model, cubePositions[i]);
float angle = 20.0f * i;
model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
lightingShader.setMat4("model", model);
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);
}
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;
layout (location = 2) in vec2 aTexCoords;
out vec3 Normal;
out vec3 FragPos;
out vec2 TexCoords;
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;
TexCoords = aTexCoords;
}
立方体片段着色器GLSLcube.fs.glsl：
#version 330 core
struct Material {
sampler2D diffuse;
sampler2D specular;
float shininess;
};
struct Light {
vec3 position;
vec3 direction;
float cutOff;
float outerCutOff;
vec3 ambient;
vec3 diffuse;
vec3 specular;
// float constant;
// float linear;
// float quadratic;
};
in vec3 Normal;
in vec3 FragPos;
in vec2 TexCoords;
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
// 将环境光下的材质颜色设置为漫反射材质颜色同样的值
vec3 ambient = light.ambient * vec3(texture(material.diffuse, TexCoords));
// 漫反射
vec3 norm = normalize(Normal);
vec3 lightDir = normalize(lightPos - FragPos);
// vec3 lightDir = normalize(-light.direction);
float diff = max(dot(norm, lightDir), 0.0);
vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, TexCoords));
// 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 * vec3(texture(material.specular, TexCoords));
// 计算衰减
// float distance = length(light.position - FragPos);
// float attenuation = 1.0 / (light.constant + light.linear * distance +
// light.quadratic * (distance * distance));
// ambient *= attenuation;
// diffuse *= attenuation;
// specular *= attenuation;
float theta = dot(lightDir, normalize(-light.direction));
if(theta > light.cutOff)
{
// 执行光照计算
vec3 result = ambient + diffuse + specular;
FragColor = vec4(result, 1.0);
}
else{ // 否则，使用环境光，让场景在聚光之外时不至于完全黑暗
float epsilon = light.cutOff - light.outerCutOff;
float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);
// 将不对环境光做出影响，让它总是能有一点光
diffuse *= intensity;
specular *= intensity;
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]投光物 - LearnOpenGL CN (learnopengl-cn.github.io)
标签：11,1.0,glm,投光物,light,float,C++,vec3,diffuse From： https://www.cnblogs.com/jiujiubashiyi/p/16591166.html