Font.cpp

#include "Font.h"
#include <GL/glew.h>
#include <cstdio>
#include <cassert>
#include <cstdlib>

void Font::SetHeight(float h) {
    m_height = h;
}

bool Font::LoadFromFile(const std::string &filename) {
    FILE *fd = fopen(filename.c_str(), "rb");
    char *ttf_buffer = new char[1<<20];
    assert(fd != 0);
    int rc = fread(ttf_buffer, 1, 1<<20, fd);
    assert(rc > 0);
    int texture_width = 512;
    int texture_height = 512;
    fclose(fd);
    stbtt_BakeFontBitmap((const unsigned char*)ttf_buffer, 0, m_height, temp_bitmap, texture_width, texture_height, 32, 96, cdata); // no guarantee this fits!
    free(ttf_buffer);
    glGenTextures(1, &ftex);
    glBindTexture(GL_TEXTURE_2D, ftex);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, texture_width, texture_height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, temp_bitmap);
    // can free temp_bitmap at this point
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    return true;
}

void Font::Draw(float x, float y, std::string text) {
    // assume orthographic projection with units = screen pixels, origin at top left
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, ftex);
    glPushMatrix();
    glBegin(GL_TRIANGLES);
    for (size_t i = 0; i < text.size(); ++i) {
        char c = text[i];
        if (c >= 32) {
            stbtt_aligned_quad q;
            stbtt_GetBakedQuad(cdata, 512, 512, c-32, &x,&y,&q,1);

            glTexCoord2f(q.s0, q.t0); glVertex2f(q.x0, q.y0);
            glTexCoord2f(q.s1, q.t1); glVertex2f(q.x1, q.y1);
            glTexCoord2f(q.s1, q.t0); glVertex2f(q.x1, q.y0);

            glTexCoord2f(q.s0, q.t0); glVertex2f(q.x0, q.y0);
            glTexCoord2f(q.s0, q.t1); glVertex2f(q.x0, q.y1);
            glTexCoord2f(q.s1, q.t1); glVertex2f(q.x1, q.y1);
        }
    }
    glEnd();
    glPopMatrix();
}

Font.h

#pragma once
#include "Resource.h"
#include "stb_truetype.h"

class Font : public Resource {
public:
    Font() {
        m_height = 16.0;
        ftex = 0;
    }

    bool LoadFromFile(const std::string &filename);

    void Draw(float x, float y, std::string text);

    void SetHeight(float h);
    float GetHeight() { return m_height; }

private:
    unsigned char temp_bitmap[512*512];
    stbtt_bakedchar cdata[96]; // ASCII 32..126 is 95 glyphs
    unsigned int ftex;
    float m_height;
};