learnOpenGL-深度测试

企业开发 2023-09-30 04:04:24 阅读次数: 0

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);
}

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