OpenGL FreeType2 位图不渲染

Posted 2023-02-16

【中文标题】OpenGL FreeType2 位图不渲染

【英文标题】：OpenGL FreeType2 bitmap not rendering

【发布时间】：2016-07-30 19:06:58

【问题描述】：

尝试使用 FreeType2 和 this online tutorial 渲染字符，但遇到了一些问题并且结果非常不规则。我查看了该网站上的其他问题here 和here 并进行了这些更正，但我仍然很困惑。我已经完成了，但位图显示不正确：

不仅如此，显示效果还取决于我要渲染的角色。有些显示为空白，而另一些显示为矩形。代码如下，任何建议将不胜感激。

主程序：

#include <iostream>
#include <fstream>
#include <vector>

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#define GLM_FORCE_RADIANS
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtx/transform.hpp>

#include <ft2build.h>
#include FT_FREETYPE_H

#include "OGLT.hpp"

OGLT Toolkit;
GLuint vao, vbo[2], shader, uniform_color, tex, uniform_tex;

static void key_callback(GLFWwindow * window, int key, int scancode, int action, int mods)
  if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
    glfwSetWindowShouldClose(window, GL_TRUE);


void MyInitialize()
  // Initialize FreeType
  FT_Library library;
  FT_Face face;
  int error = FT_Init_FreeType(&library);
  if (error)
    std::cout << "An error occurred during library initialization!\n";
  
  //error = FT_New_Face(library, "open-sans/OpenSans-Regular.ttf", 0, &face);
  error = FT_New_Face(library, "/usr/share/fonts/truetype/droid/DroidSans.ttf", 0, &face);
  if(error == FT_Err_Unknown_File_Format)
    std::cout << "The font file could be opened and read, but it appears " << 
  "that its font format is unsupported.\n";
  
  else if(error)
    std::cout << "Another error code means that the font file could not be " <<
  "opened or read, or that it is broken.\n";
  
  else std::cout << "Font file sucessfully loaded!\n";
  FT_Set_Pixel_Sizes(face, 0, 100);

  // Initialize GLEW and load shaders
  Toolkit.StartGLEW();

  // OpenGL state initialization
  glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
  glPixelStorei(GL_UNPACK_ALIGNMENT,1);
  glEnable(GL_DEPTH_TEST);
  glDepthFunc(GL_LESS);
  glEnable(GL_BLEND);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

  // Vertex buffer initialization
  FT_Load_Char(face, 'W', FT_LOAD_RENDER);
  FT_GlyphSlot g = face->glyph;

  float x = 0.0f, y = 0.0f;
  float sx = 2.0/1000.0;
  float sy = 2.0/800.0;

  float x2 = x + g->bitmap_left * sx;
  float y2 = -y - g->bitmap_top * sy;
  float w = g->bitmap.width * sx;
  float h = g->bitmap.rows * sy;

  static float letter[] = 
    x2, -y2, 0.0f,
    x2+w, -y2, 0.0f,
    x2, -y2-h, 0.0f,
    x2+w, -y2-h, 0.0f,
  ;
  static float letter_uv[] = 
    0.0f, 0.0f,
    1.0f, 0.0f,
    0.0f, 1.0f,
    1.0f, 1.0f
  ;

  glGenVertexArrays(1, &vao);
  glBindVertexArray(vao);

  glGenBuffers(2, vbo);
  glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
  glBufferData(GL_ARRAY_BUFFER, sizeof(letter), letter, GL_STATIC_DRAW);

  GLuint VertexAttributeID = 0;
  glVertexAttribPointer(VertexAttributeID, 3, GL_FLOAT, GL_FALSE, 0, 0);
  glEnableVertexAttribArray(VertexAttributeID);

  glBindBuffer(GL_ARRAY_BUFFER, vbo[1]);
  glBufferData(GL_ARRAY_BUFFER, sizeof(letter_uv), letter, GL_STATIC_DRAW);

  GLuint UvAttributeID = 1;
  glVertexAttribPointer(UvAttributeID, 2, GL_FLOAT, GL_FALSE, 0, 0);
  glEnableVertexAttribArray(UvAttributeID);

  glBindVertexArray(0);
  glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);

  glActiveTexture(GL_TEXTURE0);
  glGenTextures(1, &tex);
  glBindTexture(GL_TEXTURE_2D, tex);

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

  shader = Toolkit.LoadShaders("test_vertex.glsl", "test_fragment.glsl");
  uniform_color = glGetUniformLocation(shader, "color");
  uniform_tex = glGetUniformLocation(shader, "texture_sampler");


void MyDisplay(GLFWwindow * window)
  int width, height;
  glfwGetFramebufferSize(window, &width, &height);
  glViewport(0, 0, width, height);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glUseProgram(shader);

  glm::vec4 ColorVec = glm::vec4(0.0f, 1.0f, 0.0f, 1.0f);
  glUniform4fv(uniform_color, 1, &ColorVec[0]);
  glUniform1i(uniform_tex, 0);

  glBindVertexArray(vao);
  glActiveTexture(GL_TEXTURE0);
  glBindTexture(GL_TEXTURE_2D, tex);
  glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

  glBindVertexArray(0);
  glBindBuffer(GL_ARRAY_BUFFER, 0);
  glBindTexture(GL_TEXTURE_2D, 0);
  glUseProgram(0);


int main()
  // Initialize window
  GLFWwindow * window;

  // Initialize the library
  if(!glfwInit()) return -1;

  glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
  glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
  glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

  // Create a windowed mode window and its OpenGL context
  window = glfwCreateWindow(1000, 800, "Font Test", NULL, NULL);
  if(!window)
    glfwTerminate();
    return -1;
  

  // Make the window's context current
  glfwMakeContextCurrent(window);
  glfwSwapInterval(1);
  glfwSetKeyCallback(window, key_callback);

  MyInitialize();

  // Loop until the user closes the window
  while(!glfwWindowShouldClose(window))
    // Render here
    MyDisplay(window);
    // Swap front and back buffers
    glfwSwapBuffers(window);
    // Poll for and process events
    glfwPollEvents();
  
  glfwDestroyWindow(window);
  glfwTerminate();

  return 0;

顶点着色器：

#version 330 core

layout (location = 0) in vec3 vertex;
layout (location = 1) in vec2 vertex_uv;
out vec2 uv;

void main()
  gl_Position = vec4(vertex.xyz, 1);
  uv = vertex_uv;

片段着色器：

#version 330 core

in vec2 uv;
uniform vec4 color;
uniform sampler2D texture_sampler;
out vec4 color_out;

void main()
  color_out = vec4(1.0, 1.0, 1.0, texture(texture_sampler, uv).r) * color;

【参考方案1】：

如果您尝试显示不同的字符，您会发现您只显示了其中的一部分，这应该会导致您找到错误的原因。就是在上传uv缓冲区的代码中，一个简单的copy_paste错误：

glBufferData(GL_ARRAY_BUFFER, sizeof(letter_uv), letter, GL_STATIC_DRAW);

第三个参数应该是 letter_uv