sol2_test/src/text.cpp

#include "text.hpp"
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <ft2build.h>
#include "config.hpp"
#include FT_FREETYPE_H

void Text::render(const std::string& text, float x, float y, float scale, glm::vec3 color) {
  text_shader.use();
  glm::mat4 projection = glm::ortho(0.0f, static_cast<float>(WINDOW_WIDTH), 0.0f, static_cast<float>(WINDOW_HEIGHT));
  text_shader.setMat4("projection", projection);

  glUniform3f(glGetUniformLocation(text_shader.ID, "textColor"), color.x, color.y, color.z);
  glActiveTexture(GL_TEXTURE0);
  glBindVertexArray(text_vao);

  for(auto c : text) {
    auto& ch = characters.at(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 }
    };

    // rander glyph texture over quad
    glBindTexture(GL_TEXTURE_2D, ch.texture_id);

    // update content of VBO memory
    glBindBuffer(GL_ARRAY_BUFFER, text_vbo);
    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    // render quad
    glDrawArrays(GL_TRIANGLES, 0, 6);

    x += (ch.advance >> 6) * scale;
  }

  glBindVertexArray(0);
  glBindTexture(GL_TEXTURE_2D, 0);
}

void Text::load_font() {
  FT_Library ft;
  int fail = FT_Init_FreeType(&ft);
  dbc::check(fail == 0, "FreeType failed.");

  FT_Face face;
  fail = FT_New_Face(ft, font.c_str(), 0, &face);
  dbc::check(fail == 0, "Failed to load font.");

  // load the font bitmaps
  FT_Set_Pixel_Sizes(face, 0, font_size);
  glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

  for(unsigned char c = 0; c < 255; c++) {
    fail = FT_Load_Char(face, c, FT_LOAD_RENDER);
    dbc::check(fail == 0, $F("Failed to load char {}", int(c)));

    unsigned int texture = UINT_MAX;
    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);

    characters.try_emplace(c,
        texture,
        glm::ivec2(face->glyph->bitmap.width, face->glyph->bitmap.rows),
        glm::ivec2(face->glyph->bitmap_left, face->glyph->bitmap_top),
        static_cast<unsigned int>(face->glyph->advance.x));
  }

  // unbind
  glBindTexture(GL_TEXTURE_2D, 0);

  // cleanup
  FT_Done_Face(face);
  FT_Done_FreeType(ft);

  // create teh vao/vbo
  glGenVertexArrays(1, &text_vao);
  glGenBuffers(1, &text_vbo);
  glBindVertexArray(text_vao);
  glBindBuffer(GL_ARRAY_BUFFER, text_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);
  glBindVertexArray(0);
}