【LearnOpenGL学习笔记】——07.摄像机

1.摄像机/观察空间

以摄像机为原点的右手坐标系，x轴向右，z轴从屏幕指向自己(因此摄像机方向是z轴负方向)

如何构造模拟一个摄像机：
①摄像机位置：随便设置一个，如glm::vec3 cameraPos = glm::vec3(0.0f, 0.0f, 3.0f);
②摄像机方向：设置指向目标(如原点)，glm::vec3 cameraTarget = glm::vec3(0.0f, 0.0f, 0.0f);
然后计算方向cameraDirection = cameraTarget - cameraPos，计算完的方向指向z轴负方向，如果要让其指向正方向，则用cameraDirection = cameraPos - cameraTarget
③摄像机右轴(x轴)：定义上向量，用上向量叉乘cameraDirection，
即：glm::vec3 up = glm::vec3(0.0f, 1.0f, 0.0f);
glm::vec3 cameraRight = glm::normalize(glm::cross(up, cameraDirection));
④摄像机上轴(y轴)：cameraDirection叉乘x轴
glm::vec3 cameraUp = glm::cross(cameraDirection, cameraRight);

2.LookAt(观察矩阵)

R为右向量，U为上向量，D为方向向量，P为位置
①问题：为什么平移向量带负号？
假设摄像机在世界空间下，从原点移动到p点，则P为平移向量，但因为实际上摄像机移动的实现是世界向相反的方向移动，即在观察空间下，世界向-P方向移动等价于摄像机在世界空间下向P方向移动
②glm下的LookAt：
glm::mat4 view;
view = glm::lookAt(glm::vec3(0.0f, 0.0f, 3.0f),
glm::vec3(0.0f, 0.0f, 0.0f),
glm::vec3(0.0f, 1.0f, 0.0f));
三个参数：位置、目标、上向量

3.欧拉角

练习

代码部分

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

#include <iostream>
#include <filesystem>

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

#include <LearnOPenGL/shader_m.h>
#include <LearnOPenGL/camera.h>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb_image.h>

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

#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>
#include <iostream>

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

// 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;

// timing
float deltaTime = 0.0f;	// time between current frame and last frame
float lastFrame = 0.0f;

//mix
float mixValue = 0.2f;

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);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    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
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
   
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST)