freetype2gl3/freetype2gl3.cc

#include "gl3w.h"
#include <SDL.h>
#include <iostream>
#include <ft2build.h>
#include FT_FREETYPE_H
#include "GLProgram.h"

using namespace std;

#define WIDTH   500
#define HEIGHT  500

static FT_Library ft;
static FT_Face face;
static GLProgram program;
static GLint uniform_tex;
static GLint uniform_color;

const char vertex_shader[] =
"#version 120\n"
"\n"
"attribute vec4 coord;\n"
"\n"
"varying vec2 tex_coord_i;\n"
"\n"
"void main(void)\n"
"{\n"
"    gl_Position = vec4(coord.xy * 2.0 / 500.0, 0, 1);\n"
"    tex_coord_i = coord.zw;\n"
"}\n";

const char fragment_shader[] =
"varying vec2 tex_coord_i;\n"
"\n"
"uniform sampler2D tex;\n"
"uniform vec4 color;\n"
"\n"
"void main(void)\n"
"{\n"
"    gl_FragColor = vec4(1, 1, 1, texture2D(tex, tex_coord_i).a) * color;\n"
"}\n";

void init(void)
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
    program.create(vertex_shader, fragment_shader,
                   "coord", 0, NULL,
                   "tex", "color", NULL);
    uniform_tex = program.uniform("tex");
    uniform_color = program.uniform("color");
    program.use();
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}

void display(SDL_Window * window)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    if (FT_Load_Char(face, 'h', FT_LOAD_RENDER) != 0)
    {
        cerr << "Failed to load character" << endl;
    }
    GLuint texture_id;
    glActiveTexture(GL_TEXTURE0);
    glGenTextures(1, &texture_id);
    glBindTexture(GL_TEXTURE_2D, texture_id);
    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);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexImage2D(GL_TEXTURE_2D,
                 0,
                 GL_ALPHA,
                 face->glyph->bitmap.width,
                 face->glyph->bitmap.rows,
                 0,
                 GL_ALPHA,
                 GL_UNSIGNED_BYTE,
                 face->glyph->bitmap.buffer);
    GLuint vbo;
    glGenBuffers(1, &vbo);
    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
    GLfloat color[4] = {1, 0.6, 0, 1.0};
    glUniform1i(uniform_tex, 0);
    glUniform4fv(uniform_color, 1, color);
    GLfloat box[4][4] = {
        {0, 0, 0, 0},
        {face->glyph->bitmap.width, 0, 1, 0},
        {0, -face->glyph->bitmap.rows, 0, 1},
        {face->glyph->bitmap.width, -face->glyph->bitmap.rows, 1, 1}
    };
    glBufferData(GL_ARRAY_BUFFER, sizeof(box), box, GL_STATIC_DRAW);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    SDL_GL_SwapWindow(window);
}

int main(int argc, char *argv[])
{
    if (argc < 2)
    {
        cerr << "Usage: " << argv[0] << " <font>" << endl;
        return 1;
    }

    if (SDL_Init(SDL_INIT_VIDEO))
    {
        cerr << "Failed to initialize SDL!" << endl;
        return 1;
    }

    atexit(SDL_Quit);

    SDL_Window * window = SDL_CreateWindow(argv[0],
                                           SDL_WINDOWPOS_UNDEFINED,
                                           SDL_WINDOWPOS_UNDEFINED,
                                           WIDTH,
                                           HEIGHT,
                                           SDL_WINDOW_OPENGL);
    if (!window)
    {
        cerr << "Failed to create window!" << endl;
        SDL_Quit();
        return 2;
    }

    SDL_GLContext gl_context = SDL_GL_CreateContext(window);

    if (gl3wInit() != 0)
    {
        cerr << "Failed to gl3wInit()" << endl;
        SDL_Quit();
        return 2;
    }

    if (!gl3wIsSupported(3, 0))
    {
        cerr << "OpenGL 3.0 is not supported!" << endl;
        SDL_Quit();
        return 2;
    }

    if (FT_Init_FreeType(&ft) != 0)
    {
        cerr << "Could not FT_Init_FreeType()" << endl;
        return 2;
    }

    if (FT_New_Face(ft, argv[1], 0, &face) != 0)
    {
        cerr << "Could not load font " << argv[1] << endl;
        return 2;
    }

    FT_Set_Pixel_Sizes(face, 0, 20);

    init();
    display(window);
    SDL_Event event;
    while (SDL_WaitEvent(&event))
    {
        if (event.type == SDL_QUIT)
            break;
        else if (event.type == SDL_KEYDOWN)
        {
            if (event.key.keysym.sym == SDLK_ESCAPE)
                break;
            if (event.key.keysym.sym == SDLK_RETURN)
                display(window);
        }
    }
}