OpenGL基础23：平行光与点光源

前面几章主要是针对物体，现在开始针对光源！

一、平行光

在 OpenGL基础18：光照基础这一章里面讲了几种常见光源，先看平行光吧

一个很好的例子就是太阳光，因为离我们的距离过远，所以太阳光的特点就是“无限范围”且平行

所有的光线都是平行的，这样的话物体与光源的相对位置是不重要的，在之前的章节，Light里面都有position这一属性，对于平行光而言，这个属性就由direction替代，代码改动如下：

struct Light
{// vec3 position;vec3 direction;vec3 ambient;vec3 diffuse;vec3 specular;
};
//……
void main()
{//……vec3 lightDir = normalize(-light.direction);//……
}

GLint lightPosLoc = glGetUniformLocation(shaderObj.Program, "light.direction");
glUniform3f(lightPosLoc, -0.2f, -1.0f, -0.3f);

别忘了main()方法里的lightDir是从片段发出朝向光源的方向，所以注意符号

就这么简单，然后就可以测试看下了

如果想要在不修改着色器的情况下选择传入方向还是位置来确定是方向光还是点光源，那么可以传入vec4而并非vec3，正好：位置有位移但是方向没有位移，因此如果是想表达方向的话就将第四位w设为0.0，如果是想表达位置的话就把第四位w设为1.0，并在着色器中进行 if 判断

二、点光源

之前的例子一直就是点光源，但是非常的简单，并没有体现强度的衰减，无论物体离光源多远都被照的一样亮

衰减(Attenuation)：随着光线穿越距离的变远使得亮度也相应地减少的现象

很容易想到用一个线性公式来计算当前物体表面的光线强度，其中变量为距离，但其实这是不太真实的，在现实世界里，通常光源的亮度往往在开始的时候减少的非常快，之后随着距离的增加衰减的速度会慢下来，因此这至少是一个二次的关系

再考虑到光强和距离是一个反比关系，这样就可以得出一个基础的二次公式：

$F_{a t t}=\frac{1.0}{K_{c}+K_{l} * d+K_{q} * d^{2}}$

其中 $K_c$ 、 $K_1$ 、 $K_2$ 的取值由很多因素决定：环境、你希望光所覆盖的距离范围、光的类型等，和材质一样，设置这些参数也是一个经验的问题，在实际运用中，往往可以通过调参来获取一个尽可能满意的效果

一个参考（来源于维基百科）：

距离	常数项	一次项	二次项
7	1	0.7	1.8
13	1	0.35	0.44
20	1	0.22	0.2
32	1	0.14	0.07
50	1	0.09	0.032
65	1	0.07	0.017
100	1	0.045	0.0075
160	1	0.027	0.0028
325	1	0.014	0.0007
600	1	0.007	0.0002
3250	1	0.0014	0.000007

其中距离可以理解为光的“射程”，可以从表中看出：

$K_c$ ：常数项，通常为1，为了保证最后的光强不会超过1
$K_1$ ：线性常数，就是上面所说的随着距离越远，光强等比减弱
$K_2$ ：亮度的二次递减

理论搞定，有了前面的基础应该非常好实现，直接上完整代码：

着色器部分：

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 normal;
layout (location = 2) in vec2 texture;
out vec2 texIn;
out vec3 normalIn;
out vec3 fragPosIn;
uniform mat4 model;             //模型矩阵
uniform mat4 view;              //观察矩阵
uniform mat4 projection;        //投影矩阵
void main()
{gl_Position = projection * view * model * vec4(position, 1.0);texIn = vec2(texture.x, 1.0f - texture.y);fragPosIn = vec3(model * vec4(position, 1.0f));normalIn = mat3(transpose(inverse(model))) * normal;
}///#version 330 core
struct Material
{sampler2D diffuse;      //贴图sampler2D specular;     //镜面贴图sampler2D emission;     //放射贴图float shininess;        //反光度
};
struct Light
{vec3 position;vec3 ambient;vec3 diffuse;vec3 specular;float k0, k1, k2;
};
uniform Material material;
uniform Light light;
out vec4 color;
uniform vec3 viewPos;
in vec2 texIn;
in vec3 fragPosIn;
in vec3 normalIn;
void main()
{//环境光vec3 ambient = light.ambient * vec3(texture(material.diffuse, texIn));//漫反射光vec3 norm = normalize(normalIn);vec3 lightDir = normalize(light.position - fragPosIn);float diff = max(dot(norm, lightDir), 0.0f);vec3 diffuse = light.diffuse * (diff * vec3(texture(material.diffuse, texIn)));//镜面光vec3 viewDir = normalize(viewPos - fragPosIn);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, texIn)));//放射光贴图//vec3 emission = vec3(texture(material.emission, texIn));//点光源float dis = length(light.position - fragPosIn);float attenuation = 1.0f / (light.k0 + light.k1 * dis + light.k2 * (dis * dis));//混合diffuse *= attenuation;specular *= attenuation;vec3 result = ambient + diffuse + specular;color = vec4(result, 1.0f);
}

main.cpp：

#include<iostream>
#include<opengl/glew.h>
#define GLEW_STATIC
#include<GLFW/glfw3.h>
#include"Camera.h"
#include<glm/glm.hpp>
#include<glm/gtc/matrix_transform.hpp>
#include<glm/gtc/type_ptr.hpp>
#include"Shader.h"
#include<opengl/freeglut.h>
#include<SOIL.h>bool keys[1024];
Camera camera;
GLfloat lastX, lastY;
bool firstMouse = true;
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void cameraMove();
glm::vec3 lightPos(1.2f, 1.0f, 2.0f);
const GLuint WIDTH = 800, HEIGHT = 600;int main()
{glfwInit();glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);glfwMakeContextCurrent(window);glfwSetKeyCallback(window, key_callback);glfwSetCursorPosCallback(window, mouse_callback);glfwSetScrollCallback(window, scroll_callback);glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);glewExperimental = GL_TRUE;glewInit();int width, height;glfwGetFramebufferSize(window, &width, &height);glViewport(0, 0, width, height);Shader shaderObj("ObjVShader.txt", "ObjFShader.txt");Shader shaderLight("LightVShader.txt", "LightFShader.txt");GLfloat vertices[] = {-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};glm::vec3 position[] = {glm::vec3(0.0f, -2.0f, 0.0f),glm::vec3(0.0f, -1.0f, 0.0f),glm::vec3(0.0f, 0.0f, 0.0f),glm::vec3(-2.0f, -2.0f, 0.0f),glm::vec3(-2.0f, -1.0f, 0.0f),glm::vec3(-3.0f, -2.0f, 0.0f),glm::vec3(-2.0f, -2.0f, 1.0f),glm::vec3(-1.0f, -2.0f, -4.0f),};GLuint VBO, VAO, textureA, textureB;glGenVertexArrays(1, &VAO);glGenBuffers(1, &VBO);glBindVertexArray(VAO);glBindBuffer(GL_ARRAY_BUFFER, VBO);glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);glEnableVertexAttribArray(0);glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));glEnableVertexAttribArray(1);glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));glEnableVertexAttribArray(2);int picWidth, picHeight;glGenTextures(1, &textureA);glBindTexture(GL_TEXTURE_2D, textureA);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);unsigned char* image = SOIL_load_image("Texture/wood2.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);glGenerateMipmap(GL_TEXTURE_2D);SOIL_free_image_data(image);glGenTextures(1, &textureB);glBindTexture(GL_TEXTURE_2D, textureB);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_MIPMAP_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST_MIPMAP_NEAREST);image = SOIL_load_image("Texture/specular.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);glGenerateMipmap(GL_TEXTURE_2D);SOIL_free_image_data(image);glBindTexture(GL_TEXTURE_2D, 0);shaderObj.Use();glUniform1i(glGetUniformLocation(shaderObj.Program, "material.diffuse"), 0);glUniform1i(glGetUniformLocation(shaderObj.Program, "material.specular"), 1);GLuint lightVAO;glGenVertexArrays(1, &lightVAO);glBindVertexArray(lightVAO);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);//VBO数据已经绑定且我们就用之前的顶点数据，所以无需再管理VBOglEnableVertexAttribArray(0);glBindBuffer(GL_ARRAY_BUFFER, 0);glBindVertexArray(0);glEnable(GL_DEPTH_TEST);while (!glfwWindowShouldClose(window)){glfwPollEvents();glClearColor(0.0f, 0.0f, 0.0f, 1.0f);glClear(GL_COLOR_BUFFER_BIT);glClear(GL_DEPTH_BUFFER_BIT);cameraMove();shaderLight.Use();lightPos.x = 1.0f + sin(glfwGetTime()) * 2.0f;lightPos.y = sin(glfwGetTime() / 2.0f) * 1.0f;glm::mat4 view = camera.GetViewMatrix();glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);glm::mat4 model = glm::translate(glm::mat4(1.0f), lightPos);model = glm::scale(model, glm::vec3(0.2f));GLint modelLoc = glGetUniformLocation(shaderLight.Program, "model");GLint viewLoc = glGetUniformLocation(shaderLight.Program, "view");GLint projLoc = glGetUniformLocation(shaderLight.Program, "projection");glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));glBindVertexArray(lightVAO);glDrawArrays(GL_TRIANGLES, 0, 36);shaderObj.Use();glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, textureA);glActiveTexture(GL_TEXTURE1);glBindTexture(GL_TEXTURE_2D, textureB);GLint matSpecularLoc = glGetUniformLocation(shaderObj.Program, "material.specular");GLint matShineLoc = glGetUniformLocation(shaderObj.Program, "material.shininess");glUniform3f(matSpecularLoc, 0.0f, 0.0f, 0.0f);glUniform1f(matShineLoc, 32.0f);GLint lightPosLoc = glGetUniformLocation(shaderObj.Program, "light.position");GLint lightAmbientLoc = glGetUniformLocation(shaderObj.Program, "light.ambient");GLint lightDiffuseLoc = glGetUniformLocation(shaderObj.Program, "light.diffuse");GLint lightSpecularLoc = glGetUniformLocation(shaderObj.Program, "light.specular");GLint lightK0 = glGetUniformLocation(shaderObj.Program, "light.k0");GLint lightK1 = glGetUniformLocation(shaderObj.Program, "light.k1");GLint lightK2 = glGetUniformLocation(shaderObj.Program, "light.k2");glUniform3f(lightAmbientLoc, 0.2f, 0.2f, 0.2f);glUniform3f(lightDiffuseLoc, 1.0f, 1.0f, 1.0f);glUniform3f(lightSpecularLoc, 1.0f, 1.0f, 1.0f);glUniform1f(lightK0, 1.0f);glUniform1f(lightK1, 0.09f);glUniform1f(lightK2, 0.032f);glUniform3f(lightPosLoc, lightPos.x, lightPos.y, lightPos.z);GLint viewPosLoc = glGetUniformLocation(shaderObj.Program, "viewPos");glUniform3f(viewPosLoc, camera.Position.x, camera.Position.y, camera.Position.z);model = glm::mat4(1.0f);model = glm::rotate(model, glm::radians(57.0f), glm::vec3(-0.5f, 1.0f, 0.0f));modelLoc = glGetUniformLocation(shaderObj.Program, "model");viewLoc = glGetUniformLocation(shaderObj.Program, "view");projLoc = glGetUniformLocation(shaderObj.Program, "projection");glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));glBindVertexArray(VAO);for (int i = 0; i <= 7; i++){model = glm::translate(glm::mat4(1.0f), position[i]);model = glm::rotate(model, glm::radians(0.0f), glm::vec3(-0.5f, 1.0f, 0.0f));glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));glDrawArrays(GL_TRIANGLES, 0, 36);}glBindVertexArray(0);glfwSwapBuffers(window);}glDeleteVertexArrays(1, &VAO);glDeleteBuffers(1, &VBO);glfwTerminate();return 0;
}GLfloat deltaTime = 0.0f;
GLfloat lastFrame = 0.0f;
void cameraMove()
{GLfloat currentFrame = glfwGetTime();deltaTime = currentFrame - lastFrame;lastFrame = currentFrame;GLfloat cameraSpeed = 1.0f * deltaTime;if (keys[GLFW_KEY_W])camera.ProcessKeyboard(Camera_Movement(FORWARD), deltaTime);if (keys[GLFW_KEY_S])camera.ProcessKeyboard(Camera_Movement(BACKWARD), deltaTime);if (keys[GLFW_KEY_A])camera.ProcessKeyboard(Camera_Movement(LEFT), deltaTime);if (keys[GLFW_KEY_D])camera.ProcessKeyboard(Camera_Movement(RIGHT), deltaTime);
}void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)glfwSetWindowShouldClose(window, GL_TRUE);if (action == GLFW_PRESS)           //如果当前是按下操作keys[key] = true;else if (action == GLFW_RELEASE)            //松开键盘keys[key] = false;
}void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{camera.ProcessMouseScroll(yoffset);
}void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{if (firstMouse){lastX = xpos;lastY = ypos;firstMouse = false;}GLfloat xoffset = xpos - lastX;GLfloat yoffset = lastY - ypos;lastX = xpos;lastY = ypos;GLfloat sensitivity = 0.05;xoffset *= sensitivity;yoffset *= sensitivity;camera.ProcessMouseMovement(xoffset, yoffset);
}

可以调下参数看下别的效果