This utility will generate -Textures and the fitting .fontdef file for TTF fonts. This is useful when you want to use the flexibility of TTF fonts and want to cache the resulting image, so you don't need to regenerate it upon every program startup.

fontTextureHelper.h:

#include "Ogre.h"
#include "OgreFontManager.h"

#include <iostream>
#include <fstream>

#ifndef FONT_UNICODE
# define FONT_UNICODE //highly recommended to be used, otherwise you run into problems with non-ASCII font glyphs
#endif //FONT_UNICODE

// licensed under the do-whatever-you-want license ;)
// created by Thomas Fischer thomas{AT}thomasfischer{DOT}biz

Ogre::UTFString cache_name = "_cache";

// this code is slow, use it sparingly!
int generateFontTexture(Ogre::String fontName, bool load=false)
{
    Ogre::FontPtr font = Ogre::FontManager::getSingleton().getByName(fontName);
    if(font.isNull()) return 1;

    if(font->getType() != Ogre::FT_TRUETYPE)
        return 1;

    if(!font->isLoaded())
        font->load();

    Ogre::String texname = font->getMaterial()->getTechnique(0)->getPass(0)->getTextureUnitState(0)->getTextureName();
    

    Ogre::TexturePtr fontTexture = Ogre::TextureManager::getSingleton().getByName(texname);
    Ogre::HardwarePixelBufferSharedPtr fontBuffer = fontTexture->getBuffer();

    if(fontBuffer.isNull())
        return 1;

    // create a remporary buffer that holds the font
    size_t nBuffSize = fontBuffer->getSizeInBytes();
    Ogre::uint8* buffer = (Ogre::uint8*)calloc(nBuffSize, sizeof(Ogre::uint8)); 
    Ogre::PixelBox fontPb(fontBuffer->getWidth(), fontBuffer->getHeight(),fontBuffer->getDepth(), fontBuffer->getFormat(), buffer);          
    fontBuffer->blitToMemory(fontPb);
    
    // create new render texture
    Ogre::String texNameManual = "FontTextureRTT_"+font->getName();
    Ogre::TexturePtr t = Ogre::TextureManager::getSingleton().createManual(texNameManual,"General", Ogre::TEX_TYPE_2D, fontBuffer->getWidth(), fontBuffer->getHeight(), fontBuffer->getDepth(), 1, fontBuffer->getFormat(), Ogre::TU_RENDERTARGET);
    Ogre::TexturePtr fontTextureRTT = Ogre::TextureManager::getSingleton().getByName(texNameManual);
    fontTextureRTT->getBuffer()->blitFromMemory(fontPb);        
    
    // now render to file
    Ogre::RenderTexture* pRenderTexture = fontTextureRTT->getBuffer()->getRenderTarget();
    pRenderTexture->update();
    Ogre::String outImageName = font->getName()+ cache_name + ".png";
    pRenderTexture->writeContentsToFile(outImageName);

    // free stuff
    free(buffer);
    Ogre::TextureManager::getSingleton().remove(texNameManual);

    // save texture font infos
    Ogre::UTFString out_text = font->getName()+cache_name+"\n{\n\ttype\timage\n\tsource\t"+outImageName+"\n";

    std::vector<Ogre::Font::CodePointRange> ranges = font->getCodePointRangeList();
    for(std::vector<Ogre::Font::CodePointRange>::iterator it = ranges.begin(); it != ranges.end(); it++)
    {
        // iterate over all known glyphs
        for(Ogre::uint32 i=it->first;i<=it->second;i++)
        {
            Ogre::Font::GlyphInfo gi(0, Ogre::Font::UVRect(), 0);
            try
            {
                gi = font->getGlyphInfo(i);
            }
            catch(...)
            {
                // catch code point not found error
                continue;
            }
            
            // create character
#ifdef FONT_UNICODE
            wchar_t tmp[20];
            swprintf(tmp, 20, L"%c", i);
#else
            char tmp[20] = "";
            sprintf(tmp, "%c", i);
#endif
            out_text.append("\tglyph " + Ogre::UTFString(tmp) + " " +                         Ogre::StringConverter::toString(gi.uvRect.left)+" "+                         Ogre::StringConverter::toString(gi.uvRect.top)+" "+                         Ogre::StringConverter::toString(gi.uvRect.right)+" "+                         Ogre::StringConverter::toString(gi.uvRect.bottom)+"\n");

        }
    }
    out_text.append("}\n");

    Ogre::String defFileName = font->getName() + cache_name + ".fontdef";
    std::ofstream f;
    f.open(defFileName.c_str());
    f << out_text;
    f.close();
    Ogre::LogManager::getSingleton().logMessage("generated font cache for font "+fontName+" ("+outImageName+", "+defFileName+")");

    if(load)
    {
        // reload to find the .fontdef file
        Ogre::ResourceGroupManager::getSingleton().initialiseAllResourceGroups();
        // load now
        Ogre::FontPtr cached_font = Ogre::FontManager::getSingleton().getByName(fontName+cache_name);
        if(cached_font.isNull()) return 1;
        cached_font->load();
        return 0;
    }
    return 0;
}

// if you want to use this, use instead of the original texture name, the texture name plus cache_name (see top)
// this function creates the font cache if its not existing
int fontCacheInit(Ogre::String fontName)
{
    Ogre::FontPtr font_org = Ogre::FontManager::getSingleton().getByName(fontName);
    Ogre::FontPtr font_cache = Ogre::FontManager::getSingleton().getByName(fontName + cache_name);
    
    // base font not even existing?
    if(font_org.isNull()) return 1;
    // using texture fonts is a bit stupid ...
    if(font_org->getType() != Ogre::FT_TRUETYPE) return 1;

    int res = 0;
    if(font_cache.isNull())
        res = generateFontTexture(fontName);

    if(font_org->isLoaded()) font_org->unload();
    return res;
}

int generateAllFontTextures()
{
    Ogre::ResourceManager::ResourceMapIterator itf2 = Ogre::FontManager::getSingleton().getResourceIterator();
    while (itf2.hasMoreElements())
        generateFontTexture(itf2.getNext()->getName());

    Ogre::LogManager::getSingleton().logMessage("all font textures generated");
    return 0;
}

Example usage:

void example_usage()
{
    // use only for debugging:
    // generateAllFontTextures()

    // example: i want to use the TTF font Cyberbit in my application:
    fontCacheInit("Cyberbit");

    // from now you can use font Cyberbit_cache in your application :)
}

Link to the respective forum topic.