几何着色器的介绍

 在顶点和片段着色器之间有一个可选的着色器，叫做几何着色器(Geometry Shader)。几何着色器以一个或多个表示为一个单独基本图形（primitive）的顶点作为输入，比如可以是一个点或者三角形。几何着色器在将这些顶点发送到下一个着色阶段之前，可以将这些顶点转变为它认为合适的内容。几何着色器有意思的地方在于它可以把（一个或多个）顶点转变为完全不同的基本图形（primitive），从而生成比原来多得多的顶点。

#version 330 core
layout (points) in;
layout (line_strip, max_vertices = 2) out;

void main() {
    gl_Position = gl_in[0].gl_Position + vec4(-0.1, 0.0, 0.0, 0.0);
    EmitVertex();

    gl_Position = gl_in[0].gl_Position + vec4(0.1, 0.0, 0.0, 0.0);
    EmitVertex();

    EndPrimitive();
}

 使用这3个输出修饰符我们可以从输入的基本图形创建任何我们想要的形状。为了生成一个三角形，我们定义一个triangle_strip作为输出，然后输出3个顶点。何着色器同时希望我们设置一个它能输出的顶点数量的最大值（如果你超出了这个数值，OpenGL就会忽略剩下的顶点），我们可以在out关键字的layout标识符上做这件事。在这个特殊的情况中，我们将使用最大值为2个顶点，来输出一个line_strip。

void main() {
    gl_Position = gl_in[0].gl_Position + vec4(-0.1, 0.0, 0.0, 0.0);
    EmitVertex();

    gl_Position = gl_in[0].gl_Position + vec4(0.1, 0.0, 0.0, 0.0);
    EmitVertex();

    EndPrimitive();
}

每次我们调用EmitVertex，当前设置到gl_Position的向量就会被添加到基本图形上。无论何时调用EndPrimitive，所有为这个基本图形发射出去的顶点都将结合为一个特定的输出渲染基本图形。一个或多个EmitVertex函数调用后，重复调用EndPrimitive就能生成多个基本图形。这个特殊的例子里，发射了两个顶点，它们被从顶点原来的位置平移了一段距离，然后调用EndPrimitive将这两个顶点结合为一个单独的有两个顶点的线条。

现在你了解了几何着色器的工作方式，你就可能猜出这个几何着色器做了什么。这个几何着色器接收一个基本图形——点，作为它的输入，使用输入点作为它的中心，创建了一个水平线基本图形。如果我们渲染它，结果就会像这样：

 要注意的是glDrawArays(Points,0,4)是一个一个点去绘制的，所以每次通过几何着色器时，gl_in数组中都只有一个元素。也因此只使用gl_in[0]就能绘制出四条线。

 顶点着色器：

#version 330 core
layout (location = 0) in vec3 position;

void main()
{
    gl_Position = vec4(position.xy, 0.0f, 1.0f);
}

 片段着色器：

#version 330 core

out vec4 color;

void main()
{
	color = vec4(0.0f, 1.0f, 0.0f, 1.0f);
}

 几何着色器：

#version 330 core
layout (points) in;
layout (line_strip, max_vertices = 2) out;

void main() {
    gl_Position = gl_in[0].gl_Position + vec4(-0.1, 0.0, 0.0, 0.0);
    EmitVertex();

    gl_Position = gl_in[0].gl_Position + vec4(0.1, 0.0, 0.0, 0.0);
    EmitVertex();

    EndPrimitive();
}

 主程序：

// Std. Includes
#include <string>
#include <algorithm>
using namespace std;

// GLEW
#define GLEW_STATIC
#include <GL/glew.h>

// GLFW
#include <GLFW/glfw3.h>

// GL includes
#include "Shader.h"
#include "Camera.h"
#include "Model.h"

// GLM Mathemtics
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

// Other Libs
#include <SOIL.h>

// Properties
GLuint screenWidth = 800, screenHeight = 600;

// Function prototypes
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 Do_Movement();
void printError();
GLuint loadTexture(const GLchar* path);
GLuint loadCubemap(vector<const GLchar*> faces);

// Camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
bool keys[1024];
GLfloat lastX = 400, lastY = 300;
bool firstMouse = true;

GLfloat deltaTime = 0.0f;
GLfloat lastFrame = 0.0f;

// The MAIN function, from here we start our application and run our Game loop
int main()
{
    // Init GLFW
    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(screenWidth, screenHeight, "LearnOpenGL", nullptr, nullptr); // Windowed
    glfwMakeContextCurrent(window);

    // Set the required callback functions
    glfwSetKeyCallback(window, key_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // Options
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // Initialize GLEW to setup the OpenGL Function pointers
    glewExperimental = GL_TRUE;
    glewInit();
    glGetError(); // Debug GLEW bug fix

    // Define the viewport dimensions
    glViewport(0, 0, screenWidth, screenHeight);

    // Setup some OpenGL options
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);
    glEnable(GL_PROGRAM_POINT_SIZE);

    // Setup and compile our shaders
    Shader shader("C:\Users\32156\source\repos\LearnOpenGL\Shader\vertexShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\fragmentShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\geometryShader.txt"
    );
    
    GLfloat points[] = {
         -0.5f,  0.5f, // 左上方
         0.5f,  0.5f,  // 右上方
         0.5f, -0.5f,  // 右下方
         -0.5f, -0.5f  // 左下方
    };
    GLuint VAO, VBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(points), &points, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GL_FLOAT), (GLvoid*)0);
    glBindVertexArray(0);

    // Game loop
    while (!glfwWindowShouldClose(window))
    {
        // Set frame time
        GLfloat currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // Check and call events
        glfwPollEvents();
        Do_Movement();

        // Clear buffers
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        
        shader.Use();
        glBindVertexArray(VAO);
        glDrawArrays(GL_POINTS, 0, 4);
        glBindVertexArray(0);

        // Swap the buffers
        glfwSwapBuffers(window);
        
        printError();
    }

    glfwTerminate();
    return 0;
}

void printError()
{
    GLuint errorCode = glGetError();
    if (errorCode)
        std::cout << errorCode << std::endl;
}

// Loads a cubemap texture from 6 individual texture faces
// Order should be:
// +X (right)
// -X (left)
// +Y (top)
// -Y (bottom)
// +Z (front)
// -Z (back)
GLuint loadCubemap(vector<const GLchar*> faces)
{
    GLuint textureID;
    glGenTextures(1, &textureID);

    int width, height;
    unsigned char* image;

    glBindTexture(GL_TEXTURE_CUBE_MAP, textureID);
    for (GLuint i = 0; i < faces.size(); i++)
    {
        image = SOIL_load_image(faces[i], &width, &height, 0, SOIL_LOAD_RGB);
        glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
        SOIL_free_image_data(image);
    }
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
    glBindTexture(GL_TEXTURE_CUBE_MAP, 0);

    return textureID;
}


// This function loads a texture from file. Note: texture loading functions like these are usually 
// managed by a 'Resource Manager' that manages all resources (like textures, models, audio). 
// For learning purposes we'll just define it as a utility function.
GLuint loadTexture(const GLchar* path)
{
    //Generate texture ID and load texture data 
    GLuint textureID;
    glGenTextures(1, &textureID);
    int width, height;
    unsigned char* image = SOIL_load_image(path, &width, &height, 0, SOIL_LOAD_RGB);
    // Assign texture to ID
    glBindTexture(GL_TEXTURE_2D, textureID);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);

    // Parameters
    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_LINEAR);
    glBindTexture(GL_TEXTURE_2D, 0);
    SOIL_free_image_data(image);
    return textureID;
}

#pragma region "User input"

// Moves/alters the camera positions based on user input
void Do_Movement()
{
    // Camera controls
    if (keys[GLFW_KEY_W])
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (keys[GLFW_KEY_S])
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (keys[GLFW_KEY_A])
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (keys[GLFW_KEY_D])
        camera.ProcessKeyboard(RIGHT, deltaTime);
}

// Is called whenever a key is pressed/released via GLFW
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)
        keys[key] = true;
    else if (action == GLFW_RELEASE)
        keys[key] = false;
}

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;

    camera.ProcessMouseMovement(xoffset, yoffset);
}

void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

#pragma endregion

使用几何着色器

 运行效果：

 你可以看到，使用几何着色器，你可以使用最简单的基本图形就能获得漂亮的新玩意。因为这些形状是在你的GPU超快硬件上动态生成的，这要比使用顶点缓冲自己定义这些形状更为高效。几何缓冲在简单的经常被重复的形状比如体素（voxel）的世界和室外的草地上，是一种非常强大的优化工具。

 顶点着色器：

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 color;

out VS_OUT
{
    vec3 color; 
} vs_out;
 
void main()
{
    gl_Position = vec4(position.xy, 0.0f, 1.0f);
    vs_out.color = color;
}

 几何着色器：

#version 330 core
layout (points) in;
layout (triangle_strip, max_vertices = 5) out;

in VS_OUT {
    vec3 color;
} gs_in[];

out vec3 fColor;

void build_house(vec4 position)
{
    gl_Position = position + vec4(-0.2f, -0.2f, 0.0f, 0.0f);// 1:左下角
    EmitVertex();
    gl_Position = position + vec4( 0.2f, -0.2f, 0.0f, 0.0f);// 2:右下角
    EmitVertex();
    gl_Position = position + vec4(-0.2f,  0.2f, 0.0f, 0.0f);// 3:左上
    EmitVertex();
    gl_Position = position + vec4( 0.2f,  0.2f, 0.0f, 0.0f);// 4:右上
    EmitVertex();
    gl_Position = position + vec4( 0.0f,  0.4f, 0.0f, 0.0f);// 5:屋顶
       fColor = vec3(1.0f, 1.0f, 1.0f);
    EmitVertex();
    EndPrimitive();
}

void main()
{
    fColor = gs_in[0].color;
    build_house(gl_in[0].gl_Position);
}

 片段着色器：

#version 330 core

in vec3 fColor;
out vec4 color;

void main()
{
	color = vec4(fColor, 1.0f);
}

 主程序：

 // Setup and compile our shaders
    Shader shader("C:\Users\32156\source\repos\LearnOpenGL\Shader\vertexShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\fragmentShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\geometryShader.txt"
    );
    
    GLfloat points[] = {
        -0.5f,  0.5f, 1.0f, 0.0f, 0.0f, // 左上
         0.5f,  0.5f, 0.0f, 1.0f, 0.0f, // 右上
         0.5f, -0.5f, 0.0f, 0.0f, 1.0f, // 右下
        -0.5f, -0.5f, 1.0f, 1.0f, 0.0f  // 左下
    };
    GLuint VAO, VBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(points), &points, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GL_FLOAT), (GLvoid*)0);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GL_FLOAT), (GLvoid*)(2 * sizeof(GLfloat)));
    glBindVertexArray(0);

    // Game loop
    while (!glfwWindowShouldClose(window))
    {
        // Set frame time
        GLfloat currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // Check and call events
        glfwPollEvents();
        Do_Movement();

        // Clear buffers
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        
        shader.Use();
        glBindVertexArray(VAO);
        glDrawArrays(GL_POINTS, 0, 4);
        glBindVertexArray(0);

        // Swap the buffers
        glfwSwapBuffers(window);
        
        printError();
    }

 更新的Shade类（支持构造函数中包含第三个参数为几何着色器）

#ifndef SHADER_H
#define SHADER_H

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>

#include <GL/glew.h>

class Shader
{
public:
    GLuint Program;
    // Constructor generates the shader on the fly
    Shader(const GLchar* vertexPath,const GLchar* fragmentPath)
    {
        // 1. Retrieve the vertex/fragment source code from filePath
        std::string vertexCode;
        std::string fragmentCode;
        std::ifstream vShaderFile;
        std::ifstream fShaderFile;
        // ensures ifstream objects can throw exceptions:
        vShaderFile.exceptions(std::ifstream::badbit);
        fShaderFile.exceptions(std::ifstream::badbit);
        try
        {
            // Open files
            vShaderFile.open(vertexPath);
            fShaderFile.open(fragmentPath);
            std::stringstream vShaderStream, fShaderStream;
            // Read file's buffer contents into streams
            vShaderStream << vShaderFile.rdbuf();
            fShaderStream << fShaderFile.rdbuf();
            // close file handlers
            vShaderFile.close();
            fShaderFile.close();
            // Convert stream into string
            vertexCode = vShaderStream.str();
            fragmentCode = fShaderStream.str();
        }
        catch (std::ifstream::failure e)
        {
            std::cout << "ERROR::SHADER::FILE_NOT_SUCCESFULLY_READ" << std::endl;
        }
        const GLchar* vShaderCode = vertexCode.c_str();
        const GLchar* fShaderCode = fragmentCode.c_str();
        // 2. Compile shaders
        GLuint vertex, fragment;
        GLint success;
        GLchar infoLog[512];
        // Vertex Shader
        vertex = glCreateShader(GL_VERTEX_SHADER);
        glShaderSource(vertex, 1, &vShaderCode, NULL);
        glCompileShader(vertex);
        // Print compile errors if any
        glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);
        if (!success)
        {
            glGetShaderInfoLog(vertex, 512, NULL, infoLog);
            std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED
" << infoLog << std::endl;
        }
        // Fragment Shader
        fragment = glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fragment, 1, &fShaderCode, NULL);
        glCompileShader(fragment);
        // Print compile errors if any
        glGetShaderiv(fragment, GL_COMPILE_STATUS, &success);
        if (!success)
        {
            glGetShaderInfoLog(fragment, 512, NULL, infoLog);
            std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED
" << infoLog << std::endl;
        }
        // Shader Program
        this->Program = glCreateProgram();
        glAttachShader(this->Program, vertex);
        glAttachShader(this->Program, fragment);
        glLinkProgram(this->Program);
        // Print linking errors if any
        glGetProgramiv(this->Program, GL_LINK_STATUS, &success);
        if (!success)
        {
            glGetProgramInfoLog(this->Program, 512, NULL, infoLog);
            std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED
" << infoLog << std::endl;
        }
        // Delete the shaders as they're linked into our program now and no longer necessery
        glDeleteShader(vertex);
        glDeleteShader(fragment);

    }
    Shader(const GLchar* vertexPath, const GLchar* fragmentPath, const GLchar* geometryPath)
    {
        // 1. Retrieve the vertex/fragment source code from filePath
        std::string vertexCode;
        std::string fragmentCode;
        std::string geometryCode;
        std::ifstream vShaderFile;
        std::ifstream fShaderFile;
        std::ifstream gShaderFile;
        // ensures ifstream objects can throw exceptions:
        vShaderFile.exceptions(std::ifstream::badbit);
        fShaderFile.exceptions(std::ifstream::badbit);
        gShaderFile.exceptions(std::ifstream::badbit);
        try
        {
            // Open files
            vShaderFile.open(vertexPath);
            fShaderFile.open(fragmentPath);
            gShaderFile.open(geometryPath);
            std::stringstream vShaderStream, fShaderStream, gShaderStream;
            // Read file's buffer contents into streams
            vShaderStream << vShaderFile.rdbuf();
            fShaderStream << fShaderFile.rdbuf();
            gShaderStream << gShaderFile.rdbuf();
            // close file handlers
            vShaderFile.close();
            fShaderFile.close();
            gShaderFile.close();
            // Convert stream into string
            vertexCode = vShaderStream.str();
            fragmentCode = fShaderStream.str();
            geometryCode = gShaderStream.str();
        }
        catch (std::ifstream::failure e)
        {
            std::cout << "ERROR::SHADER::FILE_NOT_SUCCESFULLY_READ" << std::endl;
        }
        const GLchar* vShaderCode = vertexCode.c_str();
        const GLchar* fShaderCode = fragmentCode.c_str();
        const GLchar* gShaderCode = geometryCode.c_str();
        // 2. Compile shaders
        GLuint vertex, fragment, geometry;
        GLint success;
        GLchar infoLog[512];
        // Vertex Shader
        vertex = glCreateShader(GL_VERTEX_SHADER);
        glShaderSource(vertex, 1, &vShaderCode, NULL);
        glCompileShader(vertex);
        // Print compile errors if any
        glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);
        if (!success)
        {
            glGetShaderInfoLog(vertex, 512, NULL, infoLog);
            std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED
" << infoLog << std::endl;
        }
        // Fragment Shader
        fragment = glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fragment, 1, &fShaderCode, NULL);
        glCompileShader(fragment);
        // Print compile errors if any
        glGetShaderiv(fragment, GL_COMPILE_STATUS, &success);
        if (!success)
        {
            glGetShaderInfoLog(fragment, 512, NULL, infoLog);
            std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED
" << infoLog << std::endl;
        }
        geometry = glCreateShader(GL_GEOMETRY_SHADER);
        glShaderSource(geometry, 1, &gShaderCode, NULL);
        glCompileShader(geometry);
        // Print compile errors if any
        glGetShaderiv(geometry, GL_COMPILE_STATUS, &success);
        if (!success)
        {
            glGetShaderInfoLog(geometry, 512, NULL, infoLog);
            std::cout << "ERROR::SHADER::GEOMETRY::COMPILATION_FAILED
" << infoLog << std::endl;
        }
        // Shader Program
        this->Program = glCreateProgram();
        glAttachShader(this->Program, vertex);
        glAttachShader(this->Program, fragment);
        glAttachShader(this->Program, geometry);
        glLinkProgram(this->Program);
        // Print linking errors if any
        glGetProgramiv(this->Program, GL_LINK_STATUS, &success);
        if (!success)
        {
            glGetProgramInfoLog(this->Program, 512, NULL, infoLog);
            std::cout << "ERROR::SHADER::GEOMETRY::LINKING_FAILED
" << infoLog << std::endl;
        }
        // Delete the shaders as they're linked into our program now and no longer necessery
        glDeleteShader(vertex);
        glDeleteShader(fragment);

    }
    // Uses the current shader
    void Use()
    {
        glUseProgram(this->Program);
    }
};

#endif

爆破物体

 当我们说对一个物体进行爆破(Explode)的时候并不是说我们将要把之前的那堆顶点炸掉，但是我们打算把每个三角形沿着它们的法线向量移动一小段距离。效果是整个物体上的三角形看起来就像沿着它们的法线向量爆炸了一样。
 运行效果：

 顶点着色器：

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 2) in vec2 texCoords;

out VS_OUT {
    vec2 texCoords;
} vs_out;

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

void main()
{
    gl_Position = projection * view * model * vec4(position, 1.0f);
    vs_out.texCoords = texCoords;
}

 几何着色器：

#version 330 core
layout (triangles) in;
layout (triangle_strip, max_vertices = 3) out;

in VS_OUT {
    vec2 texCoords;
} gs_in[];

out vec2 TexCoords; 

uniform float time;

vec4 explode(vec4 position, vec3 normal)
{
    float magnitude = 2.0f;
    vec3 direction = normal * ((sin(time) + 1.0f) / 2.0f) * magnitude; 
    return position + vec4(direction, 0.0f);
}

vec3 GetNormal()
{
    vec3 a = vec3(gl_in[0].gl_Position) - vec3(gl_in[1].gl_Position);
    vec3 b = vec3(gl_in[2].gl_Position) - vec3(gl_in[1].gl_Position);
    return normalize(cross(a, b));
}

void main() {    
    vec3 normal = GetNormal();

    gl_Position = explode(gl_in[0].gl_Position, normal);
    TexCoords = gs_in[0].texCoords;
    EmitVertex();
    gl_Position = explode(gl_in[1].gl_Position, normal);
    TexCoords = gs_in[1].texCoords;
    EmitVertex();
    gl_Position = explode(gl_in[2].gl_Position, normal);
    TexCoords = gs_in[2].texCoords;
    EmitVertex();
    EndPrimitive();
}

 片段着色器：

#version 330 core

in vec2 TexCoords;

out vec4 color;

uniform sampler2D texture_diffuse1;

void main()
{    
    color = texture(texture_diffuse1, TexCoords);
}

 主程序：

// Setup and compile our shaders
    Shader shader("C:\Users\32156\source\repos\LearnOpenGL\Shader\vertexShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\fragmentShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\geometryShader.txt"
    );
    
    Model ourModel("D:\Download\nanosuit\nanosuit.obj");

    // Game loop
    while (!glfwWindowShouldClose(window))
    {
        // Set frame time
        GLfloat currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // Check and call events
        glfwPollEvents();
        Do_Movement();

        // Clear buffers
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        
        shader.Use();
 
        glUniform1f(glGetUniformLocation(shader.Program, "time"), glfwGetTime());
        glm::mat4 projection = glm::perspective(camera.Zoom, (float)screenWidth / (float)screenHeight, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        glUniformMatrix4fv(glGetUniformLocation(shader.Program, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
        glUniformMatrix4fv(glGetUniformLocation(shader.Program, "view"), 1, GL_FALSE, glm::value_ptr(view));

        // 传入着色器变换矩阵
        glm::mat4 model = glm::mat4(1.0f);
        model = glm::translate(model, glm::vec3(0.0f, -1.75f, 0.0f)); // Translate it down a bit so it's at the center of the scene
        model = glm::scale(model, glm::vec3(0.2f, 0.2f, 0.2f));	// It's a bit too big for our scene, so scale it down
        glUniformMatrix4fv(glGetUniformLocation(shader.Program, "model"), 1, GL_FALSE, glm::value_ptr(model));

        // 使用着色器渲染模型
        ourModel.Draw(shader);

        // Swap the buffers
        glfwSwapBuffers(window);
        
        printError();
    }

显示法向量

 运行效果：

 渲染法向量的顶点着色器：

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 normal;

out VS_OUT {
    vec3 normal;
} vs_out;

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

void main()
{
    gl_Position = projection * view * model * vec4(position, 1.0f);
    mat3 normalMatrix = mat3(transpose(inverse(view * model)));
    vs_out.normal = normalize(vec3(projection * vec4(normalMatrix * normal, 1.0)));
}

 渲染法向量的几何着色器：

#version 330 core
layout (triangles) in;
layout (line_strip, max_vertices = 6) out;

in VS_OUT {
    vec3 normal;
} gs_in[];

const float MAGNITUDE = 0.2f;

void GenerateLine(int index)
{
    gl_Position = gl_in[index].gl_Position;
    EmitVertex();
    gl_Position = gl_in[index].gl_Position + vec4(gs_in[index].normal, 0.0f) * MAGNITUDE;
    EmitVertex();
    EndPrimitive();
}

void main()
{
    GenerateLine(0); // First vertex normal
    GenerateLine(1); // Second vertex normal
    GenerateLine(2); // Third vertex normal
}

 渲染法向量的片段着色器：

#version 330 core
out vec4 color;

void main()
{
    color = vec4(1.0f, 1.0f, 0.0f, 1.0f);
}

 主程序：

// Setup and compile our shaders
    Shader shader("C:\Users\32156\source\repos\LearnOpenGL\Shader\vertexShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\fragmentShader.txt"
    );
    
    Shader shaderNormal("C:\Users\32156\source\repos\LearnOpenGL\Shader\skyboxVertexShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\skyboxFragmentShader.txt"
        , "C:\Users\32156\source\repos\LearnOpenGL\Shader\geometryShader.txt"
    );

    Model ourModel("D:\Download\nanosuit\nanosuit.obj");

    // Game loop
    while (!glfwWindowShouldClose(window))
    {
        // Set frame time
        GLfloat currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // Check and call events
        glfwPollEvents();
        Do_Movement();

        // Clear buffers
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        
        shader.Use();
        glm::mat4 projection = glm::perspective(camera.Zoom, (float)screenWidth / (float)screenHeight, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        glm::mat4 model = glm::mat4(1.0f);
        model = glm::translate(model, glm::vec3(0.0f, -1.75f, 0.0f)); // Translate it down a bit so it's at the center of the scene
        model = glm::scale(model, glm::vec3(0.2f, 0.2f, 0.2f));	// It's a bit too big for our scene, so scale it down
        glUniformMatrix4fv(glGetUniformLocation(shader.Program, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
        glUniformMatrix4fv(glGetUniformLocation(shader.Program, "view"), 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(glGetUniformLocation(shader.Program, "model"), 1, GL_FALSE, glm::value_ptr(model));
        // 使用着色器渲染模型
        ourModel.Draw(shader);

        shaderNormal.Use();
        glUniformMatrix4fv(glGetUniformLocation(shaderNormal.Program, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
        glUniformMatrix4fv(glGetUniformLocation(shaderNormal.Program, "view"), 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(glGetUniformLocation(shaderNormal.Program, "model"), 1, GL_FALSE, glm::value_ptr(model));
        ourModel.Draw(shaderNormal);


        // Swap the buffers
        glfwSwapBuffers(window);
        
        printError();