如何将OpenGL+GLFW渲染的坐标原点从左下角改为左上角？

我正在用OpenGL和GLFW开发文本编辑器，传统GUI应用以左上角为坐标原点（而非OpenGL默认的左下角），所以调整坐标原点至关重要。我需要实现窗口调整大小时，渲染内容始终锚定左上角，而非默认的左下角。

效果对比 #

初始窗口：

调整后窗口（当前默认锚定左下角）：

期望的调整后窗口效果（锚定左上角）：

最小复现代码 #

主程序代码 #

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>

class Shader
{
public:
    unsigned int ID;
    // constructor generates the shader on the fly
    // ------------------------------------------------------------------------
    Shader(const char* vertexPath, const char* fragmentPath)
    {
        // 1. retrieve the vertex/fragment source code from filePath
        std::string vertexCode;
        std::string fragmentCode;
        std::ifstream vShaderFile;
        std::ifstream fShaderFile;
        // ensure ifstream objects can throw exceptions:
        vShaderFile.exceptions (std::ifstream::failbit | std::ifstream::badbit);
        fShaderFile.exceptions (std::ifstream::failbit | std::ifstream::badbit);
        try 
        {
            // open files
            vShaderFile.open(vertexPath);
            fShaderFile.open(fragmentPath);
            std::stringstream vShaderStream, fShaderStream;
            // read file's buffer contents into streams
            vShaderStream << vShaderFile.rdbuf();
            fShaderStream << fShaderFile.rdbuf();
            // close file handlers
            vShaderFile.close();
            fShaderFile.close();
            // convert stream into string
            vertexCode   = vShaderStream.str();
            fragmentCode = fShaderStream.str();
        }
        catch (std::ifstream::failure& e)
        {
            std::cout << "ERROR::SHADER::FILE_NOT_SUCCESSFULLY_READ: " << e.what() << std::endl;
        }
        const char* vShaderCode = vertexCode.c_str();
        const char * fShaderCode = fragmentCode.c_str();
        // 2. compile shaders
        unsigned int vertex, fragment;
        // vertex shader
        vertex = glCreateShader(GL_VERTEX_SHADER);
        glShaderSource(vertex, 1, &vShaderCode, NULL);
        glCompileShader(vertex);
        checkCompileErrors(vertex, "VERTEX");
        // fragment Shader
        fragment = glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fragment, 1, &fShaderCode, NULL);
        glCompileShader(fragment);
        checkCompileErrors(fragment, "FRAGMENT");
        // shader Program
        ID = glCreateProgram();
        glAttachShader(ID, vertex);
        glAttachShader(ID, fragment);
        glLinkProgram(ID);
        checkCompileErrors(ID, "PROGRAM");
        // delete the shaders as they're linked into our program now and no longer necessary
        glDeleteShader(vertex);
        glDeleteShader(fragment);
    }
    // activate the shader
    // ------------------------------------------------------------------------
    void use() 
    { 
        glUseProgram(ID); 
    }
    // utility uniform functions
    // ------------------------------------------------------------------------
    void setBool(const std::string &name, bool value) const
    {          
        glUniform1i(glGetUniformLocation(ID, name.c_str()), (int)value); 
    }
    // ------------------------------------------------------------------------
    void setInt(const std::string &name, int value) const
    { 
        glUniform1i(glGetUniformLocation(ID, name.c_str()), value); 
    }
    // ------------------------------------------------------------------------
    void setFloat(const std::string &name, float value) const
    { 
        glUniform1f(glGetUniformLocation(ID, name.c_str()), value); 
    }
    // ------------------------------------------------------------------------
    void setMat4(const std::string &name, const float* value) const
    {
        glUniformMatrix4fv(glGetUniformLocation(ID, name.c_str()), 1, GL_FALSE, value);
    }

private:
    // utility function for checking shader compilation/linking errors.
    // ------------------------------------------------------------------------
    void checkCompileErrors(unsigned int shader, std::string type)
    {
        int success;
        char infoLog[1024];
        if (type != "PROGRAM")
        {
            glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
            if (!success)
            {
                glGetShaderInfoLog(shader, 1024, NULL, infoLog);
                std::cout << "ERROR::SHADER_COMPILATION_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
            }
        }
        else
        {
            glGetProgramiv(shader, GL_LINK_STATUS, &success);
            if (!success)
            {
                glGetProgramInfoLog(shader, 1024, NULL, infoLog);
                std::cout << "ERROR::PROGRAM_LINKING_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
            }
        }
    }
};

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

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
int screenWidth = SCR_WIDTH;
int screenHeight = SCR_HEIGHT;

int main()
{
    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

    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);

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    Shader ourShader("3.3.shader.vs", "3.3.shader.fs");

    // 改用像素坐标示例：三角形左上角锚定(0,0)，向下延伸100像素，向右延伸100像素
    float vertices[] = {
        100.0f, 100.0f, 0.0f,  1.0f, 0.0f, 0.0f,  // bottom right
         0.0f, 100.0f, 0.0f,  0.0f, 1.0f, 0.0f,  // bottom left
        50.0f,   0.0f, 0.0f,  0.0f, 0.0f, 1.0f   // top (左上角位置)
    };

    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);

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

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);

    while (!glfwWindowShouldClose(window))
    {
        processInput(window);

        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        ourShader.use();
        // 手动构造正交投影矩阵：原点在左上角，X向右递增，Y向下递增
        float projMatrix[16] = {
            2.0f / screenWidth, 0.0f, 0.0f, -1.0f,
            0.0f, -2.0f / screenHeight, 0.0f, 1.0f,
            0.0f, 0.0f, -2.0f / (1.0f - (-1.0f)), 0.0f,
            0.0f, 0.0f, 0.0f, 1.0f
        };
        ourShader.setMat4("projection", projMatrix);

        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);

    glfwTerminate();
    return 0;
}

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

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

片段着色器（3.3.shader.fs） #

#version 330 core
out vec4 FragColor;

in vec3 ourColor;

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

修改后的顶点着色器（3.3.shader.vs） #

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;

out vec3 ourColor;

uniform mat4 projection;

void main()
{
    gl_Position = projection * vec4(aPos, 1.0);
    ourColor = aColor;
}

核心修改说明 #

1. 顶点着色器加入投影矩阵：通过uniform mat4 projection接收外部传入的坐标变换矩阵，将顶点坐标转换为以左上角为原点的NDC坐标。
2. 窗口大小回调：监听窗口尺寸变化，实时更新视口和投影矩阵参数。
3. 构造正交投影矩阵：手动构造（或用GLM库）翻转Y轴的正交矩阵，将窗口左上角设为坐标原点，X轴向右，Y轴向下，完全匹配传统GUI的坐标系统。
4. 调整顶点坐标：改用像素坐标（或归一化坐标），让渲染内容的位置直接对应窗口中的实际位置，窗口缩放时自动锚定左上角。

内容的提问来源于stack exchange，提问作者xXxAirSnifferxXx