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深度测试：OpenGL将一个片段的深度值与深度缓冲的内容进行对比。执行一个深度测试，测试通过则深度缓冲将会更新为新的深度值。测试失败则片段被丢弃。
深度测试片段着色器及模版测试之后执行。
片段着色器中内置变量gl_FragCoord的z值即为深度值。

提前深度测试：允许深度测试在片段着色器之前运行。片段着色器通常开销很大。使用提前深度测试时，片段着色器不可写入深度值，因为OpenGl不能提前知道深度值。

默认禁用，glEnable(GL_DEPTH_TEST);启用

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);清楚上一帧深度缓冲

实际运用的深度缓冲是非线性的

深度冲突：两个平面或三角形z值一样，两个形状会不断切换前后顺序

防止深度冲突：
1.不要把多个物体放的太近，导致它们的一些三角形重叠
2.将进平面设置远一些，因为精度在靠近进平面时较高。（注意，进平面太远会导致近处的一些物体被裁减掉）
3.牺牲一些性能，使用更高精度的深度缓冲。大部分深度缓冲的精度都是24位，但现在大部分显卡支持32位

main.cpp

#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include "shader.h"
#include "stb_image.h"
#include <glm.hpp>
#include <gtc/matrix_transform.hpp>
#include <gtc/type_ptr.hpp>
#include "Camera.h"
#include "Model.h"Camera* myCamera = new Camera(glm::vec3(0.0f, 0.0f, 3.0f), glm::vec3(0.0f, 0.0f, -1.0f), glm::vec3(0.0f, 1.0f, 0.0f));void mouse_callback(GLFWwindow* window, double xpos, double ypos) {myCamera->mouseCb(xpos, ypos);
};void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{myCamera->scrollCb(xoffset, yoffset);
}GLfloat deltaTime = 0.0f;
GLfloat lastFrame = 0.0f;void processInput(GLFWwindow* window) {GLfloat currentFrame = glfwGetTime();deltaTime = currentFrame - lastFrame;lastFrame = currentFrame;if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)glfwSetWindowShouldClose(window, true);if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS) {myCamera->pressKeyW(deltaTime);}if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS) {myCamera->pressKeyS(deltaTime);}if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS) {myCamera->pressKeyA(deltaTime);}if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS) {myCamera->pressKeyD(deltaTime);}
}glm::vec3 pointLightPositions[] = {glm::vec3(2.0f,  10.2f,  2.0f),glm::vec3(-2.3f, 7.3f, -4.0f)
};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
};int main()
{glfwInit();glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);GLFWwindow* window = glfwCreateWindow(800, 600, "test", nullptr, nullptr);if (window == nullptr){std::cout << "Failed to create GLFW window" << std::endl;glfwTerminate();return -1;}glfwMakeContextCurrent(window);//glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);glfwSetCursorPosCallback(window, mouse_callback);glfwSetScrollCallback(window, scroll_callback);glewExperimental = GL_TRUE;if (glewInit() != GLEW_OK){std::cout << "Failed to initialize GLEW" << std::endl;glfwTerminate();return -1;}glViewport(0, 0, 800, 600);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);glEnableVertexAttribArray(0);glBindVertexArray(0);GLuint cubeVAO, cubeVBO;glGenVertexArrays(1, &cubeVAO);glBindVertexArray(cubeVAO);glGenBuffers(1, &cubeVBO);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);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);GLuint tex;glGenTextures(1, &tex);int width, height, nrComponents;unsigned char* image = stbi_load("container.jpg", &width, &height, &nrComponents, 0);if (image) {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, tex);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, format, GL_UNSIGNED_BYTE, image);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(image);}glm::mat4 model;glm::mat4 view;glm::mat4 projection;glEnable(GL_DEPTH_TEST);//深度测试函数glDepthFunc(GL_LESS);/** 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*/Shader* testShader = new Shader("test.vert", "test.frag");Shader* lightShader = new Shader("test.vert", "light.frag");while (!glfwWindowShouldClose(window)){processInput(window);glfwPollEvents();glClearColor(0.1f, 0.1f, 0.1f, 1.0f);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);testShader->Use();glUniform1i(glGetUniformLocation(testShader->getProgram(), "texture1"), 0);glBindVertexArray(cubeVAO);glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_2D, tex);view = myCamera->getViewMat4();glUniformMatrix4fv(glGetUniformLocation(testShader->getProgram(), "view"), 1, GL_FALSE, glm::value_ptr(view));projection = glm::perspective(glm::radians(myCamera->getFov()), 800.0f / 600.0f, 0.1f, 100.0f);glUniformMatrix4fv(glGetUniformLocation(testShader->getProgram(), "projection"), 1, GL_FALSE, glm::value_ptr(projection));model = glm::translate(model, glm::vec3(-1.0f, 0.0f, -1.0f));glUniformMatrix4fv(glGetUniformLocation(testShader->getProgram(), "model"), 1, GL_FALSE, glm::value_ptr(model));glDrawArrays(GL_TRIANGLES, 0, 36);model = glm::mat4(1.0f);model = glm::translate(model, glm::vec3(2.0f, 0.0f, 0.0f));glUniformMatrix4fv(glGetUniformLocation(testShader->getProgram(), "model"), 1, GL_FALSE, glm::value_ptr(model));glDrawArrays(GL_TRIANGLES, 0, 36);glBindVertexArray(planeVAO);glUniformMatrix4fv(glGetUniformLocation(testShader->getProgram(), "model"), 1, GL_FALSE, glm::value_ptr(glm::mat4(1.0f)));glDrawArrays(GL_TRIANGLES, 0, 6);glBindVertexArray(0);glfwSwapBuffers(window);}glfwTerminate();return 0;
}

顶点着色器

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoords;out vec2 TexCoords;uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;void main()
{TexCoords = aTexCoords;    gl_Position = projection * view * model * vec4(aPos, 1.0);
}

片段着色器

#version 330 core
out vec4 FragColor;in vec2 TexCoords;uniform sampler2D texture1;float near = 0.1; 
float far  = 100.0; float LinearizeDepth(float depth) 
{float z = depth * 2.0 - 1.0; // back to NDC [0,1]变换到[-1,1]（标准化设备坐标/裁剪空间）return (2.0 * near * far) / (far + near - z * (far - near));    
}void main()
{    FragColor = texture(texture1, TexCoords);//FragColor = vec4(vec3(gl_FragCoord.z), 1.0);//float depth = LinearizeDepth(gl_FragCoord.z) / far; // 为了演示除以 far//FragColor = vec4(vec3(depth), 1.0);
}