openGL：为什么屏幕上没有出现文字？

Question

我正在将我的OpenGL项目从GLUT转移到GLFW。目前我正在尝试使用FreeType库在屏幕上显示文本。我正在关注他们网站的教程，但我被困住了。我相信我已将所有内容写出来，但由于某种原因它无效。我错过了什么？

这是我的代码：

#include <iostream>
#include <stdlib.h>

// Include GLEW
#include <GL/glew.h>

#include <GLFW/glfw3.h>

#include "ft2build.h"
#include FT_FREETYPE_H

FT_Library library;
FT_Face face;

static void error_callback(int error, const char* description)
{
    fputs(description, stderr);
}

//should only be used for key press or key release
static void key_press(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GL_TRUE);
}

void render_text(const std::string &str, FT_Face face, float x, float y, float sx, float sy) {
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    const FT_GlyphSlot glyph = face->glyph;

    for (auto c : str) {
        if (FT_Load_Char(face, c, FT_LOAD_RENDER) != 0)
            continue;

        glTexImage2D(GL_TEXTURE_2D, 0, GL_R8,
            glyph->bitmap.width, glyph->bitmap.rows,
            0, GL_RED, GL_UNSIGNED_BYTE, glyph->bitmap.buffer);

        const float vx = x + glyph->bitmap_left * sx;
        const float vy = y + glyph->bitmap_top * sy;
        const float w = glyph->bitmap.width * sx;
        const float h = glyph->bitmap.rows * sy;

        struct {
            float x, y, s, t;
        } data[6] = {
            { vx, vy, 0, 0 },
            { vx, vy - h, 0, 1 },
            { vx + w, vy, 1, 0 },
            { vx + w, vy, 1, 0 },
            { vx, vy - h, 0, 1 },
            { vx + w, vy - h, 1, 1 }
        };

        glBufferData(GL_ARRAY_BUFFER, 24 * sizeof(float), data, GL_DYNAMIC_DRAW);
        glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
        glDrawArrays(GL_TRIANGLES, 0, 6);

        x += (glyph->advance.x >> 6) * sx;
        y += (glyph->advance.y >> 6) * sy;
    }

    glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
}

void Resize(GLFWwindow* window)
{
    int width, height;

    glfwGetFramebufferSize(window, &width, &height);

    glViewport(0, 0, width, height);
    glClear(GL_COLOR_BUFFER_BIT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glOrtho(-5.f, 5.f, -5.f, 5.f, 5.f, -5.f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void Setup()
{
    glEnable(GL_TEXTURE_2D);
    glEnable(GL_DEPTH_TEST); // Depth Testing
    glDepthFunc(GL_LEQUAL);
    glDisable(GL_CULL_FACE);
    glCullFace(GL_BACK);

    //used for font
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}

void Display(GLFWwindow* window)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();

    render_text("TEST", face, 0, 0, 100, 100);

    glfwSwapBuffers(window);
    glfwPollEvents();
}

void Update(GLFWwindow* window)
{
    Display(window);
}

int main(void)
{
    GLFWwindow* window;

    glfwSetErrorCallback(error_callback);

    if (!glfwInit())
        exit(EXIT_FAILURE);

    window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        exit(EXIT_FAILURE);
    }

    glfwMakeContextCurrent(window);
    glfwSwapInterval(1);

    glewExperimental = true;
    if (glewInit() != GLEW_OK)
    {
        //Problem: glewInit failed, something is seriously wrong.
        std::cout << "glewInit failed, aborting." << std::endl;
        exit(EXIT_FAILURE);
    }

    FT_Error error = FT_Init_FreeType(&library);
    if (error) {
        fprintf(stderr, "Could not init freetype library\n");
        return 1;
    }

    error = FT_New_Face(library, "Stoke-Regular.ttf", 0, &face);
    if (error == FT_Err_Unknown_File_Format) 
    { 
        std::cout << "font is unsupported" << std::endl;
        return 1;
    }
    else if (error) 
    { 
        std::cout << "font could not be read or opened" << std::endl;
        return 1;
    }

    error = FT_Set_Pixel_Sizes(face, 0, 48);
    if (error)
    {
        std::cout << "Problem adjusting pixel size" << std::endl;
        return 1;
    }

    //keyboard controls
    glfwSetKeyCallback(window, key_press);

    Resize(window);
    Setup();

    while (!glfwWindowShouldClose(window))
    {
        Update(window);
    }

    glfwDestroyWindow(window);
    glfwTerminate();
    exit(EXIT_SUCCESS);
}