14.opengl高级-模板测试

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发布于 2020-06-28 10:57:53

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发布于 2020-06-28 10:57:53

文章被收录于专栏：音视频技术学习笔记音视频技术学习笔记

1. 原理说明

1.1 模板测试像增加了一层遮罩，根据遮罩规则进行渲染

1.2 模板缓冲过程示意图,通过位0/1来控制是否通过测试

1.3 stencil test在graphics pipeline里面的位置，模板测试在深度测试之前

1.4 涉及到API

// 启用模板测试
glEnable(GL_STENCIL_TEST);

//测试完，更新模板值，要先与遮罩进行与操作，默认是FF，原值输入
glStencilMask(0xFF); // 每一位写入模板缓冲时都保持原样
glStencilMask(0x00); // 每一位在写入模板缓冲时都会变成0（禁用写入）

// 测试规则
glStencilFunc(GL_EQUAL, 1, 0xFF)
GL_ALWAYS   //永远通过深度测试
GL_NEVER    //永远不通过深度测试
GL_LESS //在片段深度值小于缓冲的深度值时通过测试
GL_EQUAL    //在片段深度值等于缓冲区的深度值时通过测试
GL_LEQUAL   //在片段深度值小于等于缓冲区的深度值时通过测试
GL_GREATER  //在片段深度值大于缓冲区的深度值时通过测试
GL_NOTEQUAL //在片段深度值不等于缓冲区的深度值时通过测试
GL_GEQUAL   在片段深度值大于等于缓冲区的深度值时通过测试

// 测试完，有三种结果，每一种测试结果可以设置是否通过(决定要不要绘制)
glStencilOp(GLenum sfail, GLenum dpfail, GLenum dppass)
GL_KEEP //保持当前储存的模板值
GL_ZERO //将模板值设置为0
GL_REPLACE  //将模板值设置为glStencilFunc函数设置的ref值
GL_INCR //如果模板值小于最大值则将模板值加1
GL_INCR_WRAP    //与GL_INCR一样，但如果模板值超过了最大值则归零
GL_DECR //如果模板值大于最小值则将模板值减1
GL_DECR_WRAP    //与GL_DECR一样，但如果模板值小于0则将其设置为最大值
GL_INVERT   //按位翻转当前的模板缓冲值

2. 实现效果-3D边框

模板测试实现边框

3. 代码说明

实现流程 1）绘制地板：glStencilMask(0x00)，缓存中都写入0，不这么做的话，整个地板的面积都会按默认操作，缓存为1，影响后面边框渲染的逻辑 2）绘制两个矩形：glStencilFunc(GL_ALWAYS, 1, 0xFF)，矩形所在的点(通过深度测试，不然后面看不到的点也有框)均设置为1 3）绘制两个矩形外框：glStencilFunc(GL_NOTEQUAL, 1, 0xFF)，放大两个矩形的体积为1.1倍，矩形不为1的点，只剩下边框的位置可以通过测试

4. 完整代码

4.1 边框顶点着色器和矩形的一样，普通的点计算，片元着色器有区别，只输出一个写死的颜色

#version 330 core
out vec4 FragColor;

void main()
{
    FragColor = vec4(0.04, 0.28, 0.26, 1.0);
}

4.2 主程序代码,重点看while循环里绘制的流程，好好理解前面提到的几个API的原理

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

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

#include "Shader.h"
#include "camera.h"
#include "model.h"

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
unsigned int loadTexture(char const * path);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

// camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;

// timeing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

glm::vec3 lightPos(1.2f, 1.0f, 2.0f);

int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    
#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif
    
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if(window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);
    
    // tell GLFW to capture our mouse
    // 这一行，不注释也是ok的，隐藏鼠标
//    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
    
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }
    
//    stbi_set_flip_vertically_on_load(true);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);
    glEnable(GL_STENCIL_TEST);
    glStencilFunc(GL_NOTEQUAL, 1, 0xFF);
    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
    
    Shader shader("1.colors.vs", "1.colors.fs");
    Shader shaderSingleColor("2.stencil_testing.vs", "2.stencil_single_color.fs");
    Shader lightCubeShader("1.light_cube.vs", "1.light_cube.fs");
    
    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float cubeVertices[] = {
        // positions          // texture Coords
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,
         0.5f, -0.5f, -0.5f,  1.0f, 0.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,

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

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

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

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

        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f
    };
    
    float planeVertices[] = {
        // positions          // texture Coords (note we set these higher than 1 (together with GL_REPEAT as texture wrapping mode). this will cause the floor texture to repeat)
         5.0f, -0.5f,  5.0f,  2.0f, 0.0f,
        -5.0f, -0.5f,  5.0f,  0.0f, 0.0f,
        -5.0f, -0.5f, -5.0f,  0.0f, 2.0f,

         5.0f, -0.5f,  5.0f,  2.0f, 0.0f,
        -5.0f, -0.5f, -5.0f,  0.0f, 2.0f,
         5.0f, -0.5f, -5.0f,  2.0f, 2.0f
    };
    
    // cube VAO
    unsigned int cubeVAO, cubeVBO;
    glGenVertexArrays(1, &cubeVAO);
    glGenBuffers(1, &cubeVBO);
    glBindVertexArray(cubeVAO);
    glBindBuffer(GL_ARRAY_BUFFER, cubeVBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(cubeVertices), &cubeVertices, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
    glBindVertexArray(0);
    
    // plane VAO
    unsigned int planeVAO, planeVBO;
    glGenVertexArrays(1, &planeVAO);
    glGenBuffers(1, &planeVBO);
    glBindVertexArray(planeVAO);
    glBindBuffer(GL_ARRAY_BUFFER, planeVBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(planeVertices), &planeVertices, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
    glBindVertexArray(0);
    
    // load textures
    // -------------
    unsigned int cubeTexture  = loadTexture("resource/marble.jpg");
    unsigned int floorTexture = loadTexture("resource/metal.png");
    
    shader.use();
    shader.setInt("texture1", 0);
    
    while (!glfwWindowShouldClose(window)) {
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;
        
        //input
        processInput(window);
        
        //render
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        
        shaderSingleColor.use();
        
        //view/projection transformations
        glm::mat4 model = glm::mat4(1.0f);
        glm::mat4 view = camera.GetViewMatrix();
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH/(float)SCR_HEIGHT, 0.1f, 100.0f);
        shaderSingleColor.setMat4("view", view);
        shaderSingleColor.setMat4("projection", projection);
        
        shader.use();
        shader.setMat4("view", view);
        shader.setMat4("projection", projection);
        
//        glStencilMask(0x00);
        //floor
        glBindVertexArray(planeVAO);
        glBindTexture(GL_TEXTURE_2D, floorTexture);
        shader.setMat4("model", glm::mat4(1.0f));
        glDrawArrays(GL_TRIANGLES, 0, 6);
        glBindVertexArray(0);
        
        // 1. 启用模板缓存
        glStencilFunc(GL_ALWAYS, 1, 0xFF);
//        glStencilMask(0xFF);// 感觉这一行可以不要,删除运行也ok
        
        // cubes
        glBindVertexArray(cubeVAO);
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, cubeTexture);
        model = glm::translate(model, glm::vec3(-1.0f, 0.0f, -1.0f));
        shader.setMat4("model", model);
        glDrawArrays(GL_TRIANGLES, 0, 36);
        
        model = glm::mat4(1.0f);
        model = glm::translate(model, glm::vec3(0.5f, 0.0f, 0.0f));
        shader.setMat4("model", model);
        glDrawArrays(GL_TRIANGLES, 0, 36);


        // 2. 绘制矩形外框
        // 2.1 设置不为1的值通过测试
        glStencilFunc(GL_NOTEQUAL, 1, 0xFF);
        // 2.2 通过测试后与0做‘与’操作，即保证写入0
        glStencilMask(0x00);
        glDisable(GL_DEPTH_TEST);
        
        shaderSingleColor.use();
        float scale = 1.1;
        glBindVertexArray(cubeVAO);
        glBindTexture(GL_TEXTURE_2D, cubeTexture);
        model = glm::mat4(1.0f);
        model = glm::translate(model, glm::vec3(-1.0f, 0.0f, -1.0f));
        model = glm::scale(model, glm::vec3(scale, scale, scale));
        shaderSingleColor.setMat4("model", model);
        glDrawArrays(GL_TRIANGLES, 0, 36);

        model = glm::mat4(1.0f);
        model = glm::translate(model, glm::vec3(0.5f, 0.0f, 0.0f));
        model = glm::scale(model, glm::vec3(scale, scale, scale));
        shaderSingleColor.setMat4("model", model);
        glDrawArrays(GL_TRIANGLES, 0, 36);
        
       // 重新初始化状态，避免出错
        glBindVertexArray(0);
        glStencilMask(0xFF);
        glStencilFunc(GL_ALWAYS, 0, 0xFF);
        glEnable(GL_DEPTH_TEST);
        
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteVertexArrays(1, &planeVAO);
    glDeleteBuffers(1, &cubeVBO);
    glDeleteBuffers(1, &planeVBO);
    
    glfwTerminate();
    return 0;
}

bool startRecord = false;
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_Y))
    {
        std::cout << "Y" << std::endl;
        startRecord = true;
    }
    
    if (glfwGetKey(window, GLFW_KEY_N))
    {
        std::cout << "N" << std::endl;

        startRecord = false;
    }
    
    if (startRecord) {
        return;
    }
    
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
    {
        glfwSetWindowShouldClose(window, true);
    }
    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
    {
        std::cout << "W" << std::endl;

        camera.ProcessKeyboard(FORWARD, deltaTime);
    }
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
    {
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    }
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
    {
        camera.ProcessKeyboard(LEFT, deltaTime);
    }
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
    {
        camera.ProcessKeyboard(RIGHT, deltaTime);
    }

}

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

void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (startRecord) {
        return;
    }
    
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }
    
    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos;
    
    lastX = xpos;
    lastY = ypos;
    
    camera.ProcessMouseMovement(xoffset, yoffset);
}

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


// 通用纹理加载方法
unsigned int loadTexture(char const * path)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);
    
    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    
    if(data)
    {
        GLenum format;
        if (nrComponents == 1)
        {
            format = GL_RED;
        }
        else if (nrComponents == 3)
        {
            format = GL_RGB;
        }
        else if (nrComponents == 4)
        {
            format = GL_RGBA;
        }
        
        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
                
        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);
        
        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to laod at path: " << path << std::endl;
        stbi_image_free(data);
    }
    
    return textureID;
}

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