2.5 变换

变换

有个易于使用，专门为OpenGL量身定做的数学库，那就是GLM。

GLM是OpenGL Mathematics的缩写，它是一个只有头文件的库，也就是说我们只需包含对应的头文件就行了，不用链接和编译。

OpenGL开发者通常使用一种内部矩阵布局，叫做列主序(Column-major Ordering)布局。GLM的默认布局就是列主序。

code

旋转、平移变换

#include "../env/glm/glm.hpp"
#include "../env/glm/gtc/matrix_transform.hpp"
#include "../env/glm/gtc/type_ptr.hpp"
#include <iostream> 

#define STB_IMAGE_IMPLEMENTATION
#include "../env/std_image.h"
#include "../env/glad.h"
#include "../env/glfw3.h"
#include <fstream>

#define WIDTH 800
#define HEIGHT 600

GLFWwindow *initialize(int width, int height);
GLuint complieVertexShader(const std::string &filename);
GLuint complieFragmentShader(const std::string &filename);
GLuint getShaderProgram(GLuint vertexShader, GLuint fragmentShader);

void framebuffer_size_callback(GLFWwindow *window, int width, int height);
void processInput(GLFWwindow *window);
std::string getShaderSource(const std::string &filename);

int main()
{
    
    
    GLFWwindow *window = initialize(WIDTH, HEIGHT);
    GLuint vertexShader = complieVertexShader("5-vertex.glsl");
    GLuint fragmentShader = complieFragmentShader("5-fragment.glsl");
    GLuint shaderProgram = getShaderProgram(vertexShader, fragmentShader);

    GLuint myVAO;
    glGenVertexArrays(1, &myVAO);
    glBindVertexArray(myVAO);

    float vertices[] = {
    
    
        //     ---- 位置 ----       ---- 颜色 ----     - 纹理坐标 -
        0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f,   // 右上
        0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f,  // 右下
        -0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // 左下
        -0.5f, 0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f   // 左上
    };

    GLuint indices[] = {
    
    
        0, 1, 3,
        2, 1, 3};

    unsigned int myVBO;
    glGenBuffers(1, &myVBO);
    glBindBuffer(GL_ARRAY_BUFFER, myVBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void *)0);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void *)(6 * sizeof(float)));

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);

    GLuint myEBO;
    glGenBuffers(1, &myEBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, myEBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    int width, height, channel;
    unsigned char *data = stbi_load("../images/container.jpg", &width, &height, &channel, 0);


    GLuint texture1;
    glGenTextures(1, &texture1);
    glBindTexture(GL_TEXTURE_2D, texture1);

    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);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
    glGenerateMipmap(GL_TEXTURE_2D);

    stbi_image_free(data);

    stbi_set_flip_vertically_on_load(true);
    data = stbi_load("../images/awesomeface.png", &width, &height, &channel, 0);

    GLuint texture2;
    glGenTextures(1, &texture2);
    glBindTexture(GL_TEXTURE_2D, texture2);

    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);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
    glGenerateMipmap(GL_TEXTURE_2D);

    stbi_image_free(data);
    
    // 激活不同的纹理单元
    glUseProgram(shaderProgram);
    GLint texture1Location = glGetUniformLocation(shaderProgram, "texture1");
    glUniform1i(texture1Location, 0);
    GLint texture2Location = glGetUniformLocation(shaderProgram, "texture2");
    glUniform1i(texture2Location, 1);

    // 获取着色器中定义的变换矩阵的位置
    GLint transformMatrixLocation = glGetUniformLocation(shaderProgram, "transform");

    while (!glfwWindowShouldClose(window))
    {
    
    
        glUseProgram(shaderProgram);
        // 激活不同的纹理单元
        // glm中的矩阵是列主序的
        glm::mat4 transform = glm::mat4(1.0f);
        // 旋转
        transform = glm::rotate(transform, (float)glfwGetTime(), glm::vec3(0.0f, 0.0f, 1.0f));
        // 缩放
        transform = glm::scale(transform, glm::vec3(0.5f, 0.5f, 1.0f ));
        // 平移
        transform = glm::translate(transform, glm::vec3(0.25f, 0.0f, 0.0f));
        // 将矩阵发送到GPU
        glUniformMatrix4fv(transformMatrixLocation, 1, GL_FALSE, glm::value_ptr(transform));

        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, texture1);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, texture2);
        glBindVertexArray(myVAO);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

        processInput(window);
        glfwSwapBuffers(window);
        glfwPollEvents();
        glClearColor(0.2, 0.3, 0.3, 1.0);
        glClear(GL_COLOR_BUFFER_BIT);
    }

    glfwTerminate();
    return 0;
}

void framebuffer_size_callback(GLFWwindow *window, int width, int height)
{
    
    
    glViewport(0, 0, width, height);
}

void processInput(GLFWwindow *window)
{
    
    
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
    {
    
    
        glfwSetWindowShouldClose(window, true);
    }
}

GLFWwindow *initialize(int width, int height)
{
    
    
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow *window = glfwCreateWindow(WIDTH, HEIGHT, "2", nullptr, nullptr);
    if (!window)
    {
    
    
        exit(-1);
    }

    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
    
    
        exit(-1);
    }

    glViewport(0, 0, width, height);

    glfwSetWindowSizeCallback(window, framebuffer_size_callback);

    return window;
}

std::string getShaderSource(const std::string &filename)
{
    
    

    std::ifstream in;
    in.open(filename, std::ios::in);
    if (!in.is_open())
    {
    
    
        exit(-1);
    }

    std::string ans, line;
    while (!in.eof())
    {
    
    
        getline(in, line);
        ans += line;
        ans.push_back('\n');
    }

    return ans;
}

GLuint complieVertexShader(const std::string &filename)
{
    
    
    const char *charPtr = nullptr;

    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    std::string vertexShaderSource = getShaderSource(filename);
    if (vertexShaderSource.empty())
        exit(-1);

    charPtr = vertexShaderSource.c_str();
    // 把这个着色器源码附加到着色器对象上，然后编译
    glShaderSource(vertexShader, 1, &charPtr, nullptr);
    glCompileShader(vertexShader);

    // 获取顶点着色器编译信息
    int success;
    char info[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
    
    
        glGetShaderInfoLog(vertexShader, 512, nullptr, info);
        std::cout << "Complie vertex shader error: " << info << std::endl;
        exit(-1);
    }

    return vertexShader;
}

GLuint complieFragmentShader(const std::string &filename)
{
    
    
    const char *charPtr = nullptr;

    // 编译片段着色器
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    std::string fragmentShaderSource = getShaderSource(filename);
    if (fragmentShaderSource.empty())
    {
    
    
        exit(-1);
    }
    charPtr = fragmentShaderSource.c_str();
    glShaderSource(fragmentShader, 1, &charPtr, nullptr);
    glCompileShader(fragmentShader);

    int success;
    char info[512];
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
    
    
        glGetShaderInfoLog(fragmentShader, 512, nullptr, info);
        std::cout << "Complie fragment shader error: " << info << std::endl;
        exit(-1);
    }

    return fragmentShader;
}

GLuint getShaderProgram(GLuint vertexShader, GLuint fragmentShader)
{
    
    
    // 创建着色器程序对象
    GLuint shaderProgram;
    shaderProgram = glCreateProgram();

    // 链接着色器到程序对象
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    // 删除着色器对象
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    return shaderProgram;
}

#version 330 core

layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoord;

uniform mat4 transform;

out vec2 ourTexCoord;

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