如何在C++中使用GLUT/OpenGL绘制文本？

#include <ft2build.h>
#include FT_FREETYPE_H

FT_Library ft;
if (FT_Init_FreeType(&ft))
    std::cout << "ERROR::FREETYPE: Could not init FreeType Library"<< std::endl;

FT_Face face;
if (FT_New_Face(ft, "path/to/font/file", 0, &face))
    std::cout << "ERROR::FREETYPE: Failed to load font"<< std::endl;

FT_Set_Pixel_Sizes(face, 0, 48);

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
for (GLubyte c = 0; c < 128; c++)
{
    if (FT_Load_Char(face, c, FT_LOAD_RENDER))
    {
        std::cout << "ERROR::FREETYTPE: Failed to load Glyph"<< std::endl;
        continue;
    }
    GLuint texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexImage2D(
        GL_TEXTURE_2D,
        0,
        GL_RED,
        face->glyph->bitmap.width,
        face->glyph->bitmap.rows,
        0,
        GL_RED,
        GL_UNSIGNED_BYTE,
        face->glyph->bitmap.buffer
    );
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    Character character = {
        texture,
        glm::ivec2(face->glyph->bitmap.width, face->glyph->bitmap.rows),
        glm::ivec2(face->glyph->bitmap_left, face->glyph->bitmap_top),
        face->glyph->advance.x
    };
    Characters.insert(std::pair<GLchar, Character>(c, character));
}

std::string text = "Hello, World!";
glUseProgram(shaderProgram);
glUniform3f(glGetUniformLocation(shaderProgram, "textColor"), 1.0f, 1.0f, 1.0f);
glActiveTexture(GL_TEXTURE0);
for (char c : text)
{
    Character ch = Characters[c];
    GLfloat xpos = x + ch.Bearing.x * scale;
    GLfloat ypos = y - (ch.Size.y - ch.Bearing.y) * scale;

    GLfloat w = ch.Size.x * scale;
    GLfloat h = ch.Size.y * scale;
    glBindTexture(GL_TEXTURE_2D, ch.TextureID);
    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(GLfloat) * 6 * 4, glm::value_ptr(glm::vec4(xpos, ypos + h, 0.0, 0.0)));
    glBufferSubData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 6 * 4, sizeof(GLfloat) * 6 * 4, glm::value_ptr(glm::vec4(xpos, ypos, 0.0, 0.0)));
    glBufferSubData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 12 * 4, sizeof(GLfloat) * 6 * 4, glm::value_ptr(glm::vec4(xpos + w, ypos, 0.0, 1.0)));
    glBufferSubData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 18 * 4, sizeof(GLfloat) * 6 * 4, glm::value_ptr(glm::vec4(xpos + w, ypos + h, 0.0, 1.0)));
    glDrawArrays(GL_TRIANGLES, 0, 6);
    x += (ch.Advance >> 6) * scale;
}
glBindVertexArray(0);
glBindTexture(GL_TEXTURE_2D, 0);