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src/02_text_description.cpp
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278
src/02_text_description.cpp
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/*
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* MIT License
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*
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* Copyright (c) 2026 Mark Allyn
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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/*
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* 02_text_description.cpp
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* Author: Mark Allyn
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* Component: 02_text_description
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*
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* FreeType-based text renderer. Loads ASCII glyphs into GL_RED textures
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* and renders them as textured quads into whichever viewport is active.
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*/
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#include "02_text_description.h"
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#include <ft2build.h>
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#include FT_FREETYPE_H
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#include <cstdio>
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#include <fstream>
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#include <sstream>
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/* Global singleton used by all components. */
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TextRenderer g_text_renderer;
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/* ------------------------------------------------------------------ */
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/* Internal helpers */
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/* ------------------------------------------------------------------ */
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static bool read_file(const std::string& path, std::string& out) {
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std::ifstream f(path);
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if (!f.is_open()) {
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fprintf(stderr, "[02_text] cannot open shader: %s\n", path.c_str());
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return false;
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}
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std::ostringstream ss;
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ss << f.rdbuf();
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out = ss.str();
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return true;
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}
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static GLuint compile_shader_src(const char* source, GLenum type) {
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GLuint shader = glCreateShader(type);
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glShaderSource(shader, 1, &source, nullptr);
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glCompileShader(shader);
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GLint ok = 0;
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glGetShaderiv(shader, GL_COMPILE_STATUS, &ok);
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if (!ok) {
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char log[512];
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glGetShaderInfoLog(shader, 512, nullptr, log);
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fprintf(stderr, "[02_text] shader compile error:\n%s\n", log);
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}
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return shader;
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}
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/* ------------------------------------------------------------------ */
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/* TextRenderer public methods */
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/* ------------------------------------------------------------------ */
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bool TextRenderer::initialize_shaders() {
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std::string vert_src, frag_src;
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if (!read_file(SHADER_DIR "02_text_description_vert.glsl", vert_src)) return false;
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if (!read_file(SHADER_DIR "02_text_description_frag.glsl", frag_src)) return false;
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GLuint vert = compile_shader_src(vert_src.c_str(), GL_VERTEX_SHADER);
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GLuint frag = compile_shader_src(frag_src.c_str(), GL_FRAGMENT_SHADER);
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shader_program_ = glCreateProgram();
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glAttachShader(shader_program_, vert);
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glAttachShader(shader_program_, frag);
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glLinkProgram(shader_program_);
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GLint ok = 0;
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glGetProgramiv(shader_program_, GL_LINK_STATUS, &ok);
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if (!ok) {
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char log[512];
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glGetProgramInfoLog(shader_program_, 512, nullptr, log);
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fprintf(stderr, "[02_text] shader link error:\n%s\n", log);
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glDeleteShader(vert);
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glDeleteShader(frag);
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return false;
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}
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glDeleteShader(vert);
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glDeleteShader(frag);
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/* VAO/VBO for one glyph quad: 6 vertices × 4 floats (xy + uv). */
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glGenVertexArrays(1, &vao_);
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glGenBuffers(1, &vbo_);
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glBindVertexArray(vao_);
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glBindBuffer(GL_ARRAY_BUFFER, vbo_);
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glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 6 * 4, nullptr, GL_DYNAMIC_DRAW);
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glEnableVertexAttribArray(0);
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glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(float), reinterpret_cast<void*>(0));
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glBindBuffer(GL_ARRAY_BUFFER, 0);
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glBindVertexArray(0);
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/* Bind text_sampler uniform to texture unit 0. */
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glUseProgram(shader_program_);
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glUniform1i(glGetUniformLocation(shader_program_, "text_sampler"), 0);
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glUseProgram(0);
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#if DEBUG_SHADER_COMPILE
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fprintf(stdout, "[02_text] shaders compiled and linked OK\n");
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#endif
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return true;
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}
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bool TextRenderer::initialize_font(const std::string& font_path, unsigned int font_size) {
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FT_Library ft_lib;
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if (FT_Init_FreeType(&ft_lib)) {
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fprintf(stderr, "[02_text] FreeType init failed\n");
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return false;
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}
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FT_Face ft_face;
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if (FT_New_Face(ft_lib, font_path.c_str(), 0, &ft_face)) {
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fprintf(stderr, "[02_text] cannot load font: %s\n", font_path.c_str());
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FT_Done_FreeType(ft_lib);
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return false;
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}
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FT_Set_Pixel_Sizes(ft_face, 0, font_size);
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/* Upload each printable ASCII glyph as a GL_RED texture. */
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glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
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for (unsigned char c = 32; c < 127; c++) {
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if (FT_Load_Char(ft_face, c, FT_LOAD_RENDER)) {
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fprintf(stderr, "[02_text] failed to load glyph 0x%02x\n", c);
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continue;
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}
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GLuint tex = 0;
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glGenTextures(1, &tex);
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glBindTexture(GL_TEXTURE_2D, tex);
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glTexImage2D(
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GL_TEXTURE_2D, 0, GL_RED,
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static_cast<GLsizei>(ft_face->glyph->bitmap.width),
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static_cast<GLsizei>(ft_face->glyph->bitmap.rows),
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0, GL_RED, GL_UNSIGNED_BYTE,
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ft_face->glyph->bitmap.buffer
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);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
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glyph_character ch;
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ch.texture_id = tex;
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ch.size_x = static_cast<int>(ft_face->glyph->bitmap.width);
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ch.size_y = static_cast<int>(ft_face->glyph->bitmap.rows);
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ch.bearing_x = ft_face->glyph->bitmap_left;
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ch.bearing_y = ft_face->glyph->bitmap_top;
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ch.advance = static_cast<unsigned int>(ft_face->glyph->advance.x);
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characters_[static_cast<char>(c)] = ch;
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}
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glBindTexture(GL_TEXTURE_2D, 0);
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FT_Done_Face(ft_face);
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FT_Done_FreeType(ft_lib);
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fprintf(stdout, "[02_text] font loaded: %s at %u px\n", font_path.c_str(), font_size);
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return true;
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}
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void TextRenderer::render_text(const std::string& text,
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float x, float y, float scale,
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float color_r, float color_g, float color_b) {
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glUseProgram(shader_program_);
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glUniform3f(glGetUniformLocation(shader_program_, "text_color"),
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color_r, color_g, color_b);
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glActiveTexture(GL_TEXTURE0);
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glBindVertexArray(vao_);
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for (std::string::const_iterator it = text.cbegin(); it != text.cend(); ++it) {
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char c = *it;
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if (characters_.count(c) == 0) {
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/* Advance by a fixed amount for unknown characters. */
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x += 10.0f * scale;
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continue;
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}
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const glyph_character& ch = characters_.at(c);
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float xpos = x + static_cast<float>(ch.bearing_x) * scale;
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float ypos = y - static_cast<float>(ch.size_y - ch.bearing_y) * scale;
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float w = static_cast<float>(ch.size_x) * scale;
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float h = static_cast<float>(ch.size_y) * scale;
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if (w > 0.0f && h > 0.0f) {
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float vertices[6][4] = {
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{ xpos, ypos + h, 0.0f, 0.0f },
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{ xpos, ypos, 0.0f, 1.0f },
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{ xpos + w, ypos, 1.0f, 1.0f },
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{ xpos, ypos + h, 0.0f, 0.0f },
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{ xpos + w, ypos, 1.0f, 1.0f },
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{ xpos + w, ypos + h, 1.0f, 0.0f }
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};
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glBindTexture(GL_TEXTURE_2D, ch.texture_id);
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glBindBuffer(GL_ARRAY_BUFFER, vbo_);
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glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices);
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glDrawArrays(GL_TRIANGLES, 0, 6);
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}
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x += static_cast<float>(ch.advance >> 6) * scale;
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}
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glBindVertexArray(0);
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glBindTexture(GL_TEXTURE_2D, 0);
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glUseProgram(0);
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}
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float TextRenderer::get_text_width(const std::string& text, float scale) const {
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float width = 0.0f;
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for (std::string::const_iterator it = text.cbegin(); it != text.cend(); ++it) {
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char c = *it;
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if (characters_.count(c) == 0) {
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width += 10.0f * scale;
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continue;
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}
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width += static_cast<float>(characters_.at(c).advance >> 6) * scale;
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}
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return width;
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}
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void TextRenderer::set_projection(int w, int h) {
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/* Column-major orthographic matrix mapping pixel space [0,w]x[0,h]
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* to NDC. Near=-1, far=1 (depth unused for 2D text). */
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float fw = static_cast<float>(w);
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float fh = static_cast<float>(h);
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float proj[16] = {
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2.0f / fw, 0.0f, 0.0f, 0.0f,
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0.0f, 2.0f / fh, 0.0f, 0.0f,
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0.0f, 0.0f, -1.0f, 0.0f,
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-1.0f, -1.0f, 0.0f, 1.0f
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};
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glUseProgram(shader_program_);
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glUniformMatrix4fv(
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glGetUniformLocation(shader_program_, "projection"),
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1, GL_FALSE, proj
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);
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glUseProgram(0);
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}
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void TextRenderer::cleanup() {
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for (std::map<char, glyph_character>::iterator it = characters_.begin();
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it != characters_.end(); ++it) {
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glDeleteTextures(1, &it->second.texture_id);
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}
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characters_.clear();
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if (vao_) { glDeleteVertexArrays(1, &vao_); vao_ = 0; }
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if (vbo_) { glDeleteBuffers(1, &vbo_); vbo_ = 0; }
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if (shader_program_) { glDeleteProgram(shader_program_); shader_program_ = 0; }
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}
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