Text rendering in OpenGL using FreeType - c++

Question

I'm trying to display some simple text in OpenGL, but all I get is a black screen. I'm using cglm (glm for c), glad, and glfw. Here is my code:
#include <iostream>
#include <map>
#include <string>
#include <vendor/glad/glad.h>
#include <vendor/GLFW/glfw3.h>
#include <vendor/cglm/cglm.h>
#include <ft2build.h>
#include FT_FREETYPE_H
// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
const char *vertexShaderSource =
"#version 330 core\n"
"layout (location = 0) in vec4 vertex; // <vec2 pos, vec2 tex>\n"
"out vec2 TexCoords;\n"
"uniform mat4 projection;\n"
"void main()\n"
"{\n"
" gl_Position = projection * vec4(vertex.xy, 0.0, 1.0);\n"
" TexCoords = vertex.zw;\n"
"};\n";
const char *fragmentShaderSource =
"#version 330 core\n"
"in vec2 TexCoords;\n"
"out vec4 color;\n"
"uniform sampler2D text;\n"
"uniform vec3 textColor;\n"
"void main()\n"
"{ \n"
" vec4 sampled = vec4(1.0, 1.0, 1.0, texture(text, TexCoords).r);\n"
" color = vec4(textColor, 1.0) * sampled;\n"
"};\n";
typedef struct my_vec3
{
float x;
float y;
float z;
} my_vec3;
typedef struct my_vec2
{
int x;
int y;
} my_vec2;
typedef struct Character
{
unsigned int TextureID; // ID handle of the glyph texture
my_vec2 Size; // Size of glyph
my_vec2 Bearing; // Offset from baseline to left/top of glyph
unsigned int Advance; // Horizontal offset to advance to next glyph
} Character;
void framebuffer_size_callback(GLFWwindow *window, int width, int height);
void processInput(GLFWwindow *window);
void RenderText(GLuint shader, std::string text, float x, float y, float scale, my_vec3 color);
unsigned int VAO, VBO;
std::map<GLchar, Character> Characters;
int main()
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
GLFWwindow *window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
if (window == NULL)
{
printf("Failed to create GLFW window");
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
printf("Failed to initialize GLAD");
return -1;
}
glEnable(GL_CULL_FACE);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
printf("ERROR::SHADER::VERTEX::COMPILATION_FAILED %s\n", infoLog);
}
unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
printf("ERROR::SHADER::FRAGMENT::COMPILATION_FAILED %s\n", infoLog);
}
unsigned int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success)
{
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
printf("ERROR::SHADER::PROGRAM::LINKING_FAILED %s\n", infoLog);
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
mat4 projection;
glm_mat4_identity(projection);
glm_ortho(0.0, static_cast<float>(SCR_WIDTH), 0.0f, static_cast<float>(SCR_HEIGHT), 0.01, 100.0, projection);
// glm_perspective(4.8, (float)SCR_WIDTH/(float)SCR_WIDTH, 0.01, 100.0, projection);
glUseProgram(shaderProgram);
glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "projection"), 1, GL_FALSE, &projection[0][0]);
FT_Library ft;
if (FT_Init_FreeType(&ft))
{
std::cout << "ERROR::FREETYPE: Could not init FreeType Library" << std::endl;
return -1;
}
std::string font_name = "/home/filip/Downloads/arial/arial.ttf";
FT_Face face;
if (FT_New_Face(ft, font_name.c_str(), 0, &face))
{
std::cout << "ERROR::FREETYPE: Failed to load font" << std::endl;
return -1;
}
else
{
FT_Set_Pixel_Sizes(face, 0, 48);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
for (unsigned char 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;
}
unsigned int 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);
my_vec2 size;
size.x = face->glyph->bitmap.width;
size.y = face->glyph->bitmap.rows;
my_vec2 bearing;
bearing.x = face->glyph->bitmap_left;
bearing.y = face->glyph->bitmap_top;
Character character = {
texture,
size,
bearing,
static_cast<unsigned int>(face->glyph->advance.x)};
Characters.insert(std::pair<char, Character>(c, character));
}
glBindTexture(GL_TEXTURE_2D, 0);
}
FT_Done_Face(face);
FT_Done_FreeType(ft);
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 6 * 4, NULL, GL_DYNAMIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(float), 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
while (!glfwWindowShouldClose(window))
{
processInput(window);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
my_vec3 color1;
color1.x = 0.5;
color1.y = 0.8;
color1.z = 0.2;
my_vec3 color2;
color2.x = 0.3;
color2.y = 0.7;
color2.z = 0.9;
RenderText(shaderProgram, "This is sample text", 125.0f, 125.0f, 1.0f, color1);
RenderText(shaderProgram, "(C) LearnOpenGL123.com", 370.0f, 370.0f, 0.5f, color2);
glfwSwapBuffers(window);
glfwPollEvents();
}
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)
{
glViewport(0, 0, width, height);
}
void RenderText(GLuint shader, std::string text, float x, float y, float scale, my_vec3 color)
{
glUseProgram(shader);
glUniform3f(glGetUniformLocation(shader, "textColor"), color.x, color.y, color.z);
glActiveTexture(GL_TEXTURE0);
glBindVertexArray(VAO);
std::string::const_iterator c;
for (c = text.begin(); c != text.end(); c++)
{
Character ch = Characters[*c];
float xpos = x + ch.Bearing.x * scale;
float ypos = y - (ch.Size.y - ch.Bearing.y) * scale;
float w = ch.Size.x * scale;
float h = ch.Size.y * scale;
float vertices[6][4] = {
{xpos, ypos + h, 0.0f, 0.0f},
{xpos, ypos, 0.0f, 1.0f},
{xpos + w, ypos, 1.0f, 1.0f},
{xpos, ypos + h, 0.0f, 0.0f},
{xpos + w, ypos, 1.0f, 1.0f},
{xpos + w, ypos + h, 1.0f, 0.0f}};
glBindTexture(GL_TEXTURE_2D, ch.TextureID);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices); // be sure to use glBufferSubData and not glBufferData
glBindBuffer(GL_ARRAY_BUFFER, 0);
glDrawArrays(GL_TRIANGLES, 0, 6);
x += (ch.Advance >> 6) * scale; // bitshift by 6 to get value in pixels (2^6 = 64 (divide amount of 1/64th pixels by 64 to get amount of pixels))
}
glBindVertexArray(0);
glBindTexture(GL_TEXTURE_2D, 0);
}
I've been following this tutorial. The program compiles and runs without any errors, except that it does not render anything and I can not seem to figure out why.

Answer 1

It seems that you are placing your text on plane z=0
" gl_Position = projection * vec4(vertex.xy, **0.0**, 1.0);\n"
But your camera is looking to -Z (standard camera) from -0.01 to -100.0f.
glm_ortho(0.0, static_cast<float>(SCR_WIDTH), 0.0f, static_cast<float>(SCR_HEIGHT), **0.01, 100.0**, projection);
You can solve it just moving your text a little bit to the -Z axis. A value between the range you have specified in the Zmin, Zmax parameters of the glm_ortho function. Just to be inside the box that ortho is defining.
" gl_Position = projection * vec4(vertex.xy, **-3.0**, 1.0);\n"
It doesn't mind because it is an orthographic projection. Objects have the same size no matter how depth they are.
More details about projection can be found here http://www.songho.ca/opengl/gl_transform.html