OpenGL绘制四边形绕(5,4)旋转90度，使用转换矩阵方法

要绘制一个四边形绕(5,4)旋转90度，可以按照以下步骤使用转换矩阵方法：

1. 定义四边形的四个顶点坐标，可以使用数组表示，例如：

float vertices[] = {
   4.0f, 3.0f, 0.0f, // 右上角
   2.0f, 4.0f, 0.0f, // 左上角
   3.0f, 2.0f, 0.0f, // 右下角
   1.0f, 1.0f, 0.0f  // 左下角
};

2. 创建一个旋转矩阵，将四边形绕原点逆时针旋转90度，可以使用以下代码：

glm::mat4 rotation = glm::rotate(glm::mat4(1.0f), glm::radians(90.0f), glm::vec3(0.0f, 0.0f, 1.0f));

这里使用了glm库的旋转函数，第一个参数是一个4x4的单位矩阵，第二个参数是旋转角度，第三个参数是旋转轴向量，这里选择了z轴作为旋转轴。

3. 创建一个平移矩阵，将四边形平移到(5,4)的位置，可以使用以下代码：

glm::mat4 translation = glm::translate(glm::mat4(1.0f), glm::vec3(5.0f, 4.0f, 0.0f));

这里使用了glm库的平移函数，第一个参数是一个4x4的单位矩阵，第二个参数是平移向量。

4. 将旋转矩阵和平移矩阵相乘，得到最终的变换矩阵：

glm::mat4 transform = translation * rotation;

5. 将变换矩阵传递给着色器，在顶点着色器中将顶点坐标乘以变换矩阵，即可实现四边形的旋转和平移，例如：

#version 330 core

layout (location = 0) in vec3 aPos;

uniform mat4 transform;

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

6. 最后使用glDrawArrays函数绘制四边形。

完整的代码示例：

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char *vertexShaderSource = "#version 330 core\n"
    "layout (location = 0) in vec3 aPos;\n"
    "uniform mat4 transform;\n"
    "void main()\n"
    "{\n"
    "   gl_Position = transform * vec4(aPos, 1.0f);\n"
    "}\0";
const char *fragmentShaderSource = "#version 330 core\n"
    "out vec4 FragColor;\n"
    "void main()\n"
    "{\n"
    "   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
    "}\n\0";

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);

    // 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);

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

    // build and compile our shader zprogram
    // ------------------------------------
    // vertex shader
    int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // fragment shader
    int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // link shaders
    int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        4.0f, 3.0f, 0.0f, // 右上角
        2.0f, 4.0f, 0.0f, // 左上角
        3.0f, 2.0f, 0.0f, // 右下角
        1.0f, 1.0f, 0.0f  // 左下角
    };
    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

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

    // note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    // You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
    // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
    // glBindVertexArray(0);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // create transformations
        glm::mat4 transform = glm::translate(glm::mat4(1.0f), glm::vec3(5.0f, 4.0f, 0.0f));
        transform = glm::rotate(transform, glm::radians(90.0f), glm::vec3(0.0f, 0.0f, 1.0f));

        // get matrix's uniform location and set matrix
        unsigned int transformLoc = glGetUniformLocation(shaderProgram, "transform");
        glUniformMatrix4fv(transformLoc, 1, GL_FALSE, glm::value_ptr(transform));

        // render container
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
        // glBindVertexArray(0); // no need to unbind it every time 

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteProgram(shaderProgram);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

在这个示例中，我们使用了GLM库来进行矩阵计算，以及glfw和glad库来创建窗口和加载OpenGL函数。在渲染循环中，我们先创建了变换矩阵，将其上传到着色器中，然后绘制四边形。要注意的是，在绘制四边形之前，我们需要先绑定VAO和使用着色器程序。