高級OpenGL之立方體貼圖中反射

箱子反射天空盒的具體實現代碼：

#include <iostream>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <fstream>
#include <sstream>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <map>
//#include <boost/filesystem.cpp>
#define STB_IMAGE_IMPLEMENTATION
#include <stb_image.h>
#include <vector>
#include "Shader.h"
#include "Camera.h"
#define _USE_MATH_DEFINES
#include<math.h>
using namespace std;
void framebuffer_size_callback(GLFWwindow* windows, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void processInput(GLFWwindow *window);
void scroll_callback(GLFWwindow *window, double xoffset, double yoffset);
unsigned int loadTexture(const char *path);
unsigned int loadCubemap(vector<std::string>faces);
//settings
const unsigned int SCR_WIDTH = 1280;
const unsigned int SCR_HEIGHT = 720;


Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = (float)SCR_HEIGHT / 2.0f;
float lastY = (float)SCR_WIDTH / 2.0f;
bool firstMouse = true;
unsigned int cubemapVAO, cubemapVBO;
unsigned int cubeVAO, cubeVBO;
//timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;
vector<std::string>faces
{
	"D:/opengltask/LearnOpenGL_master/resources/textures/skybox/right.jpg",
	"D:/opengltask/LearnOpenGL_master/resources/textures/skybox/left.jpg",
	"D:/opengltask/LearnOpenGL_master/resources/textures/skybox/top.jpg",
	"D:/opengltask/LearnOpenGL_master/resources/textures/skybox/bottom.jpg",
	"D:/opengltask/LearnOpenGL_master/resources/textures/skybox/back.jpg",
	"D:/opengltask/LearnOpenGL_master/resources/textures/skybox/front.jpg"
};
//立方體貼圖頂點座標數據
float skyboxVertices[] = {
	// positions          
	-1.0f,  1.0f, -1.0f,
	-1.0f, -1.0f, -1.0f,
	1.0f, -1.0f, -1.0f,
	1.0f, -1.0f, -1.0f,
	1.0f,  1.0f, -1.0f,
	-1.0f,  1.0f, -1.0f,

	-1.0f, -1.0f,  1.0f,
	-1.0f, -1.0f, -1.0f,
	-1.0f,  1.0f, -1.0f,
	-1.0f,  1.0f, -1.0f,
	-1.0f,  1.0f,  1.0f,
	-1.0f, -1.0f,  1.0f,

	1.0f, -1.0f, -1.0f,
	1.0f, -1.0f,  1.0f,
	1.0f,  1.0f,  1.0f,
	1.0f,  1.0f,  1.0f,
	1.0f,  1.0f, -1.0f,
	1.0f, -1.0f, -1.0f,

	-1.0f, -1.0f,  1.0f,
	-1.0f,  1.0f,  1.0f,
	1.0f,  1.0f,  1.0f,
	1.0f,  1.0f,  1.0f,
	1.0f, -1.0f,  1.0f,
	-1.0f, -1.0f,  1.0f,

	-1.0f,  1.0f, -1.0f,
	1.0f,  1.0f, -1.0f,
	1.0f,  1.0f,  1.0f,
	1.0f,  1.0f,  1.0f,
	-1.0f,  1.0f,  1.0f,
	-1.0f,  1.0f, -1.0f,

	-1.0f, -1.0f, -1.0f,
	-1.0f, -1.0f,  1.0f,
	1.0f, -1.0f, -1.0f,
	1.0f, -1.0f, -1.0f,
	-1.0f, -1.0f,  1.0f,
	1.0f, -1.0f,  1.0f
};

//箱子頂點數據和法向量數據
float vertices[] = {
	-0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
	0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
	0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
	0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
	-0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
	-0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,

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

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

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

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

	-0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
	0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
	0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
	0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
	-0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
	-0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f
};
glm::mat4 model = glm::mat4(1.0f);
int main()
{
	//glfw:initialize and configure
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	GLFWwindow *window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "cube_map", 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);

	glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);


	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}
	glEnable(GL_DEPTH_TEST);	//啓動深度測試
	unsigned int  cubeTexture;
	//cubeTexture = loadTexture("D:/opengltask/LearnOpenGL_master/resources/textures/container.jpg");
	unsigned int cubemapTexture = loadCubemap(faces);
	//對於立方體貼圖的VAO
	glGenVertexArrays(1, &cubemapVAO);
	glGenBuffers(1, &cubemapVBO);
	glBindVertexArray(cubemapVAO);
	glBindBuffer(GL_ARRAY_BUFFER, cubemapVBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(skyboxVertices), &skyboxVertices, GL_STATIC_DRAW);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
	glBindVertexArray(0);


	//對於箱子的VAO
	glGenVertexArrays(1, &cubeVAO);
	glGenBuffers(1, &cubeVBO);
	glBindVertexArray(cubeVAO);
	glBindBuffer(GL_ARRAY_BUFFER, cubeVBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), &vertices, GL_STATIC_DRAW);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)0);
	glEnableVertexAttribArray(1);
	glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(3*sizeof(float)));
	glBindVertexArray(0);


	Shader boxShader = Shader("cube_reflection.vs", "cube_reflection.fs");	//箱子對應頂點着色器和片段着色器代碼
	Shader skyboxShader = Shader("cubemap.vs", "cubemap.fs");	//天空盒對應頂點着色器和片段着色器

	while (!glfwWindowShouldClose(window))
	{
		float currentFrame = glfwGetTime();
		deltaTime = currentFrame - lastFrame;
		lastFrame = currentFrame;


		//處理鍵盤輸入
		processInput(window);

		glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
		boxShader.use();
		glm::mat4 view = camera.GetViewMatrix();		//取矩陣左上角得3*3矩陣來移除變換矩陣得位移部分
		glm::mat4 projection= glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
		boxShader.setMat4("model", model);
		boxShader.setMat4("view", view);
		boxShader.setMat4("projection", projection);
		boxShader.setVec3("cameraPos", camera.Position);
		/*DrawTwoContainers(boxShader);*/
		glBindVertexArray(cubeVAO);
		//glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_CUBE_MAP, cubemapTexture);
		glDrawArrays(GL_TRIANGLES, 0, 36);
		glBindVertexArray(0);
		glDepthFunc(GL_LEQUAL);	//深度緩衝將會填充上天空盒的1.0，所以需要保證天空盒在值小於或等於深度緩衝時通過深度測試
		skyboxShader.use();
		view = glm::mat4(glm::mat3(camera.GetViewMatrix()));		//取矩陣左上角得3*3矩陣來移除變換矩陣的位移部分
		skyboxShader.setMat4("view", view);
		skyboxShader.setMat4("projection", projection);
		glBindVertexArray(cubemapVAO);
		glBindTexture(GL_TEXTURE_CUBE_MAP, cubemapTexture);
		glDrawArrays(GL_TRIANGLES, 0, 36);
		glBindVertexArray(0);
		glDepthFunc(GL_LESS);	
		glfwSwapBuffers(window);
		glfwPollEvents();
	}
	glDeleteVertexArrays(1, &cubeVAO);
	glDeleteVertexArrays(1, &cubemapVAO);
	glDeleteBuffers(1, &cubeVBO);
	glDeleteBuffers(1, &cubemapVBO);
	glfwTerminate();
	return 0;
}
void framebuffer_size_callback(GLFWwindow* window, int width, int height)	//視口根據窗口大小調整的函數，兩個整數表示窗口的新維度
{
	glViewport(0, 0, width, height);
}
void processInput(GLFWwindow *window)	//輸入的控制
{
	if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
		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);
	if (glfwGetKey(window, GLFW_KEY_L) == GLFW_PRESS)
	model = glm::rotate(model, (float)(M_PI / 360.0), glm::vec3(0.0f, 1.0f, 0.0f));
	if (glfwGetKey(window, GLFW_KEY_R) == GLFW_PRESS)
	model = glm::rotate(model, (float)(-M_PI / 360.0), glm::vec3(0.0f, 1.0f, 0.0f));
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)	//	glfwGetKey函數需要一個窗口以及一個按鍵作爲輸入，函數將會返回這個按鍵是否正在被按下
		glfwSetWindowShouldClose(window, true);
}
void mouse_callback(GLFWwindow* window, double xpos, double ypos)	//鼠標回調函數
{
	if (firstMouse)
	{
		lastX = xpos;
		lastY = ypos;
		firstMouse = false;
	}
	float xoffset = xpos - lastX;
	float yoffset = lastY - ypos;	//相反的，因爲y座標是從底部往頂部依次增大的
	lastX = xpos;
	lastY = ypos;
	camera.ProcessMouseMovement(xoffset, yoffset);
}
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)	//鼠標滾輪的回調函數
{
	camera.ProcessMouseScroll(yoffset);
}
unsigned int loadTexture(char const *path)
{
	unsigned int texture_id;
	glGenTextures(1, &texture_id);
	int width, height, nrChannels;
	unsigned char *data = stbi_load(path, &width, &height, &nrChannels, 0);
	if (data)
	{
		GLenum format;	//unsigned int 類型的別稱
		if (nrChannels == 1)
			format = GL_RED;
		else if (nrChannels == 3)
			format = GL_RGB;
		else if (nrChannels == 4)
			format = GL_RGBA;
		glBindTexture(GL_TEXTURE_2D, texture_id);
		glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

		glGenerateMipmap(GL_TEXTURE_2D);

		stbi_image_free(data);
	}
	else
	{
		std::cout << "Failed to load texture at path:" << path << std::endl;
	}

	return texture_id;
}
unsigned int loadCubemap(vector<std::string> faces)	//創建立方體貼圖
{
	unsigned int textureID;
	glGenTextures(1, &textureID);
	glBindTexture(GL_TEXTURE_CUBE_MAP, textureID);

	int width, height, nrChannels;
	for (unsigned int i = 0; i < faces.size(); i++)
	{
		unsigned char *data = stbi_load(faces[i].c_str(), &width, &height, &nrChannels, 0);
		if (data)
		{
			glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
			stbi_image_free(data);
		}
		else
		{
			std::cout << "Cubemap texture failed to load at path: " << faces[i] << std::endl;
			stbi_image_free(data);
		}
	}
	glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_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);

	return textureID;
}

箱子頂點着色器代碼：

#version 330 core
layout(location=0) in vec3 aPos;
layout(location=1)in vec3 aNormal;
out vec3 Normal;
out vec3 Position;

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

void main()
{
	Normal=mat3(transpose(inverse(model)))*aNormal;
	Position=vec3(model*vec4(aPos,1.0));
	gl_Position=projection*view*model*vec4(aPos,1.0);
}

箱子片段着色器代碼：

#version 330 core

out vec4 FragColor;
in vec3 Normal;
in vec3 Position;

uniform vec3 cameraPos;
uniform samplerCube skybox;


void main()
{   
   vec3 I=normalize(Position-cameraPos);
   vec3 R=reflect(I,normalize(Normal)); 
   FragColor=vec4(texture(skybox,R).rgb,1.0);
}

天空盒頂點着色器代碼：

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

天空盒片段着色器代碼：

#version 330 core
in vec3 TexCoords;
uniform samplerCube skybox;
out vec4 FragColor;
void main()
{
	FragColor=texture(skybox,TexCoords);
}