OpenGL教程：5. GLM数学库

GLM是OpenGL的数学库，提供了mat矩阵、vec向量等数据结构的运算，非常方便。

//
// Created by inver on 2022/9/12.
//
#include <iostream>
#include "glad/glad.h"
#include "GLFW/glfw3.h"
#include "Shader.h"

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

int main() {
    //  GLM简单介绍
    //  定义四维向量
    glm::vec4 vec(1.0f, 0.0f, 0.0f, 1.0f);
    // 定义变换矩阵，默认为单位矩阵：
    //  1   0   0   0
    //  0   1   0   0
    //  0   0   1   0
    //  0   0   0   1
    glm::mat4 trans = glm::mat4(1.0f);
    //  将单位矩阵弄成平移矩阵
    //  1   0   0   x
    //  0   1   0   y
    //  0   0   1   z
    //  0   0   0   1
    //  translate函数用来创建平移矩阵，第一个参数是作用矩阵，第二个参数是向量
    trans = glm::translate(trans, glm::vec3(1.0f, 1.0f, 0.0f));     //后面的vec3的值对应x、y、z
    vec = trans * vec;
    std::cout << vec.x << ", " << vec.y << ", " << vec.z << std::endl;
    //  此时向量变换为(2, 1, 0)


    //  rotate函数用来创建旋转矩阵，scale用于创建缩放矩阵
    glm::mat4 mat2 = glm::mat4(1.0f);
    mat2 = glm::rotate(mat2, glm::radians(90.0f),
                       glm::vec3(0.0f, 0.0f, 1.0f));     //第二个参数是旋转角度（radians转为弧度），第二个参数为旋转轴，这里绕z
    mat2 = glm::scale(mat2, glm::vec3(0.5f, 0.5f, 0.5f));   //第二个参数是三个坐标的缩放倍数，这里缩小两倍
    //  调用上面两个函数会使得mat2自动相乘，并且默认右乘，所以顺序反过来：先缩放、后旋转
    vec = mat2 * vec;
    std::cout << vec.x << ", " << vec.y << ", " << vec.z << std::endl;
    //  此时向量变换为(-0.5, 1, 0)

    //  初始化
    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, "GLM矩阵变换", nullptr, nullptr);
    if (window == nullptr) {
        std::cout << "Error: Fail to create window! \n";
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress)) {
        std::cout << "Error: Fail to initialize GLAD! \n";
        return -1;
    }

    float vertices[] = {
            -0.5f, -0.5f, 0.0f,
            0.0f, 0.5f, 0.0f,
            0.5f, -0.5f, 0.0f
    };

    unsigned int vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_DYNAMIC_DRAW);

    unsigned int vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *) nullptr);
    glEnableVertexAttribArray(0);

    std::string vsh = "shaders\glm\glm.vsh";
    std::string fsh = "shaders\glm\glm.fsh";
    Shader shader(vsh, fsh);
    shader.use();

    while (!glfwWindowShouldClose(window)) {
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glm::mat4 mat = glm::mat4(1.0f);
        //  角度随时间变化，所以是动态的旋转
        mat = glm::rotate(mat, (float) glfwGetTime(), glm::vec3(0.0f, 0.0f, 1.0f));

        //  获取uniform变量transform的地址
        unsigned int transformLoc = glGetUniformLocation(shader.id, "transform");
        //  将mat2矩阵传给transform（第一个参数是地址，第二个变量是矩阵的个数，第三个确认是否转置，第四个是矩阵的参数）
        glUniformMatrix4fv(transformLoc, 1, GL_FALSE, glm::value_ptr(mat));

        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    glDeleteProgram(shader.id);
    glfwTerminate();

}

顶点着色器

#version 330 core
layout (location = 0) in vec3 aPos;

uniform mat4 transform;

void main(){
    gl_Position = transform * vec4(aPos, 1.0);
}

片元着色器

#version 330 core
out vec4 FragColor;

void main(){
    FragColor = vec4(0.5f, 0.5f, 0.2f, 1.0f);
}