Creating Bitmap Fonts using bmfontgen

Artikel
08/30/2006

Author: Gary Kacmarcik (garykac@microsoft.com)
Revision: 14 September 2006

Introduction

The BMFontGen application is a command line utility which can convert a TrueType or OpenType font into a bitmap font. A bitmap font consists of one or more images plus an XML descriptor file which identifies the location of each glyph in the bitmap images along with additional font metric data. These bitmap fonts can be useful in game development where one cannot assume that the game platform provides a font renderer.

This document describes how to create bitmap fonts and how to use them in the XNA programming environment. The BMFontGen application is part of the XNAExtras package, the latest version of which can be downloaded here.

Features

There are a number of bitmap font creation applications available. The bmfontgen application differs from most in that it:

Supports Unicode
Supports extracting more than 256 characters
Allows the set of included characters to be specified as ranges or from a file
Permits individual glyphs to be replaced with custom images

Limitations

While BMFontGen strives to provide full Unicode character support, it is worth noting the following limitations:

While special glyphs like ligatures, non-spacing marks and contextual forms will be extracted as part of the font, currently no special support is provided for these characters.
Surrogate characters are not supported.

Other limitations include:

No codepages other than Unicode are supported
Glyphs are not packed as tightly as possible in the image bitmap
Italic fonts may have the top or bottom tails clipped

Some of these limitations may be removed in later versions.

I : Basic Operation

Using BMFontGen to create fonts

The most basic operation of bmfontgen requires that you specify a font and an output file name.

    bmfontgen -name "Courier New" -size 12 -output "courier"

This command will create a bitmap font with the default set of characters. The font will be based on 12 point "Courier New" and be saved it in "courier.xml" and "courier-0.png".

Alternately, you can use the Windows interface to choose a font using the -fontdialog option:

    bmfontgen -fontdialog -output "font"

This will bring up the standard Windows font selection dialog and allow you to select the font interactively.

Using bitmap fonts created by BMFontGen in XNA

To load and render bitmap fonts created with BMFontGen, you'll want to make use of the BitmapFont class. This rest of this section contains sample code that makes use of the BitmapFont class to display a single text string in a window.

The basic procedure is:

Include a using reference to XNAExtras
Add bitmapfont.cs to your project
Create the font by instantiating BitmapFont and passing it the XML font descriptor file generated by bmfontgen
Render text in your drawing code using the BitmapFont::DrawString method.
Reset the font whenever the device changes (using BitmapFont::Reset)

Here is the sample code for a simple application that displays a string. Most of the code is from the XNA template - the font-related code is highlighted in green.

 using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using XNAExtras;

namespace SimpleFontTest
{
    class SimpleFontTest : Microsoft.Xna.Framework.Game
    {
        private BitmapFont m_font;
        private Microsoft.Xna.Framework.Components.GraphicsComponent m_graphics;

        public SimpleFontTest()
        {
            m_graphics = new Microsoft.Xna.Framework.Components.GraphicsComponent();
            this.GameComponents.Add(m_graphics);
        }

        protected override void OnStarting()
        {
            base.OnStarting();
            m_graphics.GraphicsDevice.DeviceReset += new EventHandler(GraphicsDevice_DeviceReset);

            // create the font
            m_font = new BitmapFont("font.xml");

            LoadResources();
        }

        void GraphicsDevice_DeviceReset(object sender, EventArgs e)
        {
            LoadResources();
        }

        void LoadResources()
        {
            // reset the font when the GraphicsDevice changes
            m_font.Reset(m_graphics.GraphicsDevice);
        }

        protected override void Draw()
        {
            // Make sure we have a valid device
            if (!m_graphics.EnsureDevice())
                return;

            m_graphics.GraphicsDevice.Clear(Color.CornflowerBlue);
            m_graphics.GraphicsDevice.BeginScene();

            // draw the string
            m_font.DrawString(20, 20, Color.DarkBlue, "Sample string");

            m_graphics.GraphicsDevice.EndScene();
            m_graphics.GraphicsDevice.Present();
        }
    }
}

A number of overloads for DrawString are provided that allow parameters like the (x,y) position and color to be omitted. When these parameters are not present, the text color and position is determined by the previous DrawString call.

Note that the BitmapFont class currently provides only basic text rendering capabilities. It does not justify text or provide word wrap capabilities. It also does not support most advanced text rendering options, like bidirectional (or even right-to-left) text, complex ligatures, non-spacing marks and contextual forms.

II : Advanced Options

Choosing an appropriate text rendering hint

While not required, choosing an appropriate text rendering hint value when creating the font can improve the appearance of the bitmap font, especially at small point sizes.

The TextRenderingHint is specified via the -trh option. There are four possible hint values that can be used:

aa : Anti-aliased
aa-grid : Anti-aliased with grid fit
1bpp : One bit per pixel
1bpp-grid : One bit per pixel with grid fit

For example, to set the hint to enable anti-aliasing, the following option would be used:

    -trh aa

The difference between the various options is demonstrated in the following table, which shows Times New Roman 10pt using each of the text rendering hint options:


aa	aa-grid	1bpp	1bpp-grid

Note that at smaller point sizes, the aa hint can result in a text that is not as bright as that produced with one of the gridfit hints. The point at which this happens varies from font to font, but seems common at font sizes less than 12 pts. The following table shows Times New Roman at different point sizes rendered using the aa hint:


Times 8pt	Times 10pt	Times 12pt	Times 14pt	Times 16pt

To help avoid these rendering problems, BMFontgen uses the following defaults: aa-grid for point sizes less than 12; and aa for point sizes 12 and larger. Users are strongly encouraged to evaluate the different TextRenderingHints when creating fonts that are 12 points or less in size.

Using an options file

Option files are text files that contain all of the options needed to create a single font. They are useful when the number of options being specified on the command line becomes large, or when certain extended options are required.

A simple option file is:

    -name "Courier New"
   -size 12
   -output courier12

Note that there is one option per line in an option file. To use an options file to create a font, use the -optfile option with the name of the options file.

    bmfontgen -optfile font_options.txt

The following rules apply to options in an option file:

No line may be longer than 128 characters
Each option line must begin with a hyphen ('-')
Lines that do not begin with a hyphen are treated as comments and are ignored.
Comments may not appear on the same line as an option

Any option that can be used on the command line can also be specified in an options file. There is also an additional set of options (called "extended options" - see the next section for more information) that are only valid when used within an options file. In addition, some options (like -range and -source) are permitted multiple times in an options file, whereas they are only allowed once on the command line.

Extended options

While most options can be specified directly on the command line, there is a small set of options that can only be specified in an options file. These options are known as extended options. These options are considered to be more complex than the other options because of the number of parameters that they require and it is this complexity that restricts them to the options file.

Currently, the only extended option is -custom.

Information on each extended option can be found in Appendix A.

Adding custom glyphs to a font

It is often desirable to add a few special characters to a font, so that these symbols can be written out in a string of text. Custom characters can be added (or used to replace existing characters) by using the -custom extended option.

As an example, to replace the letter 'q' in a font with a custom image, simply add the following extended option to your options file (custom glyphs can only be specified in an options files):

    -custom 0071 abxy.png 0 0 20 20 16 21 0 true

This will replace Unicode codepoint 0071 ('q') with the portion of the "abxy.png" bitmap defined by the (0,0, 20,20) rectangle. The next three options are the baseline (measured from the top of the bitmap rectangle), advance width and the left side bearing. These three options are used to position the glyph relative to the other characters and to specify the spacing around the glyph, as shown in the following figure.


"abxy.png"	Custom glyph extracted from "abxy.png"with metrics

The last option is the "force white" option - set it to 'true' to force the glyph to always be displayed using white, regardless of the current font color. This is useful when you're providing a full color replacement glyph, as in this example.

When these option are used with a 14 point "Comic Sans MS" font, the following bitmap font is created.

Font bitmap with the 'q' characterreplaced by a custom glyph

Once the font has been created in this manner, the custom glyph will be displayed instead of the original character. In this example, drawing the string "Press the q button to switch weapons" would display as follows:

When used in a real game, a character other then 'q' would likely be chosen. Any valid Unicode character can be replaced in this fashion.

Creating fonts with international characters

By default, the font will contain the standard A-Z upper and lower case plus the standard punctuation marks (all Unicode code points from 0020 to 007E). While this range is appropriate for English and a few other languages, there are many languages which require additional characters.

To change the range of characters that are included in the generated font, you can use the -range option. A single range can be specified directly on the command line:

    -range 0000-00ff

or multiple ranges can be specified in an options file:

    -range 0020-007e
   -range 00a0-00ff
   -range 0152-0153

Range values must be specified as 4 hex digits and must be connect by a single hyphen. No spaces are allowed in the range specification.

If you specify a range value, then the default range (0020-007E) will not be used. Thus, if you want basic Latin character support (including punctuation marks), you need to add characters from this range into your range specifications.

Here is a sample options file that creates a Russian font from "Lucida Sans Unicode"

    -name "Lucida Sans Unicode"
   -size 14
   -output russian
   -range 0020-007e
   -range 0400-04ff

Drawing the string "Спасибо Вам за то, что Вы спасли мне жизнь!" with this font produces:

Creating CJK fonts

Chinese, Japanese and Korean fonts are somewhat more challenging to generate because of the large number of glyphs present in those fonts. There can be 10's of thousands of characters in a single CJK font, most of which will not be used. While this problem can be partially addressed using the -range option, that approach is unwieldy and potentially problematic since there is no guarantee that the defined ranges contain all of the required characters.

To address this problem, BMFontGen permits a character-source file to be defined that contains the set of all characters that needs to be included in the font. Characters do not need to occur uniquely in this file – a character may occur multiple times in this file and it will be defined only once in the created font. This allows a dialog script or even source code to be used as a character-source file. The only restriction is that the file must be UTF-8 encoded (with/without a BOM char).

Character-source file are specified with the -source option. A single character-source file can be specified directly on the command line:

    -source game_dialog.txt

or multiple character-source files can be specified in an options file:

    -source dialog.cs
   -source messages.cs
   -source about.cs

While this option was originally intended to provide support for CJK fonts, it can be used when creating fonts for any language. The -source option can be used as a safeguard to ensure that all required characters are present.

Here is a sample options file that creates a Japanese font from "ＭＳＰゴシック", including a standard set of Latin and Japanese characters plus all characters from the "japanese.txt" file.

    -name "ＭＳ Ｐゴシック"
   -size 14
   -output japanese
   -bmsize 256
   -range 0020-007e
   -range 3000-3100
   -source japanese.txt

Using this font to display the string "お兄ちゃ…　お兄ちゃんなんか大っ嫌い！" produces this output:

Appendix A
Summary of available options

This section provides a brief description of each option available in BMFontGen. Unless otherwise specified, these options may be specified on the command line and may only occur once. Extended options (that can only be specified in an options file) and options that are permitted more than once (but only in an options file), are noted in the description.

-blackbg

Normally the font image bitmap is created with a transparent background and white text. This can make it difficult to review the font to evaluate how well the glyphs are formed since most image display programs show the image on a white background. This option will force the bitmap to be created with a black background so that the characters show up clearly.

Note that this option should not be used when creating the final font bitmap.

-bmsize size

By default, the font bitmap size is 256x256. This option allows the user to change the size of each bitmap to any value from 64 to 1024. The size value is used to set both the height and the width of the font bitmap. Sizes that are an integral power of 2 are recommended, but not required (a warning is issued when a non-power-of-2 value is used).

-bold

Create a bold version of the specified font. This option is ignored if the –fontdialog option is used.

Other font style options include -italic, -strikeout and -underline.

-custom ch file x y w h base aw lsb fw

Define a custom glyph to replace the standard glyph (if any) in the font for the specified character. The character is automatically added to the list of characters included in the font (so a separate -range option is not necessary).

Note: This is an extended option and my only appear in an options file.

The arguments for this option are:

ch : the Unicode character, encoded as a 4 hex digit value
file : the file that contains the custom glyph bitmap
x, y : the origin of the glyph in the bitmap
w, h : the width and height of the glyph in the bitmap
base : the baseline of the glyph, measured from the origin of the glyph's bounding rectangle
aw : Advance Width – the horizontal distance to advance the pen after drawing this character
lsb : Left Side Bearing – the horizontal distance from the pen starting position to the left side of the glyph bitmap
fw : Force White - "true" to force this character to alway use Color.White when rendering, regardless of the current font color

The -custom option may appear multiple times, but each option should describe a separate character. If multiple custom options appear for the same character, only the last one will be used.

-fontdialog

Use the OS’s font selection dialog to interactively select the font name, size and style.

This option can be used instead of the -name and -size options. If this option is used, the -bold, -italic, -strikeout and -underline options are ignored.

-italic

Create an italic version of the specified font. This option is ignored if the –fontdialog option is used.

Other font style options include -bold, -strikeout and -underline.

-listfonts

Produce a list of available fonts and print it to stdout.

Note that because of codepage issues, fonts that have localized names may not display correctly when written to the console. To avoid this problem, use –listfontsfile which will write the list of available fonts into a file.

-listfontsfile fontfilename

Same as –listfonts, but the font list is written into a UTF-8 encoded text file instead of printed to stdout. This option is useful when there are installed fonts that have localized names since these names can be mangled when printed to the console.

-name fontname

The name of the font to create.

This option, along with the -size option, is required unless the –fontdialog option is used.

-nowarn-all

Don’t issue any warnings.

-nowarn-missingglyph

Don’t issue a warning if a glyph in the requested range is missing from the font.

-optfile filename

Read the options from the specified file instead of from the command line. Note that some options ("extended options") can only be specified in an options file. See "Using an options file" in Section II for more information.

-output base-output-name

The base filename for the output files. The base filename is restricted to no more than 50 characters in length.

For basic fonts, the extension ".png" and ".xml" will be added to the font image and font xml description files, respectively. If more than one image is required to encode the font, a numeric value will be added to the base filename.

This is a required option.

-range start-end

Specify a start and end character range to include in the font. By default the range is 0020 to 007E. The start and end character values must be Unicode code points and must be encoded as 4 hex digit values.

If you specify a range, then the default range (0020-007E) will not be used. If you want to include basic latin support, then you need to include this range in your range specification.

Note that the -range option may only be specified once on the command line.

To define multiple disjoint character ranges for a font, use this option in an options file. The -range option may be specified multiple times in an option file and the union of all defined ranges will be used for the font. See "Using an options file" in Section II for more information about using option files.

-size size

Specify the size of the font in points. Only font sizes from 7 to 50 points are supported.

-source filename

Specify a character-source file that contains the set of characters that should be included in the font. The file must be UTF-8 encoded (note that 7-bit ASCII encoded files are valid UTF-8 files); the 3-byte UTF-8 BOM character is not required and is ignored if present.

When this option is used, the default character range (0020-007E) will be ignored. If this option is used in conjunction with the -range option, the font will contain the union of all characters specified by the two options.

Note that the -source option may only be specified once on the command line.

To define multiple character-source files, use this option in an options file. The -source option may be specified multiple times in an option file and the union of all characters will be used for the font. See "Using an options file" in Section II for more information about using option files.

-strikeout

Create a strikeout version of the specified font. This option is ignored if the –fontdialog option is used.

Other font style options include -bold, -italic and -underline.

-trh hint

Set the TextRenderingHint, which can help the GDI+ text rendering engine produce better font bitmaps. The hint value can be any of:

1bpp : Use one bit per pixel
1bpp-grid : Use one bit per pixel and fit the glyphs to a display grid
aa : Enable anti-aliasing
aa-grid : Enable anti-aliasing and fit the glyphs to a display grid

-underline

Create an underlined version of the specified font. This option is ignored if the –fontdialog option is used.

Other font style options include -bold, -italic and -strikeout.

-v

Verbose output - display lots of extraneous information while the font is being created.

BMFontGen.zip

Comments

Anonymous
August 30, 2006
As mentioned in a&nbsp;previous post, there is a clear need for a bitmap font generator that provides...
Anonymous
August 30, 2006
The reason that antialiased text looks so much darker may be that you're not performing gamma correction correctly when antialiasing.
Anonymous
August 31, 2006
Thank-you for this resource. When I found out I'd have to write a bitmap font display class for XNA I was dismayed. Your work has saved me a big chunk of time.

Something that I changed in your BitmapFont class was the ability to pass in a file path for the fonts. This allows the fonts to reside in some content directory rather than with the executable:

public BitmapFont(string strFilePath, string strFontFilename)
{
m_strFilePath = strFilePath;
...

...
xd.Load(strFilePath+strFontFilename);
...
}

public void Reset(GraphicsDevice device)
{
m_sb = new SpriteBatch(device);
foreach (KeyValuePair<int, BitmapInfo> kv in m_dictBitmapID2BitmapInfo)
m_dictBitmapID2Texture[kv.Key] = Texture2D.FromFile(device, m_strFilePath + kv.Value.strFilename, kv.Value.nX, kv.Value.nY);
}

Thanks again!
- Dave
Anonymous
August 31, 2006
Thank you for this tool Gary ! It works perfectly !
Anonymous
September 02, 2006
As with most systems we have to have a way to display text to the screen, over the last few hours I have
Anonymous
September 03, 2006
Great tool! Ohw and I experienced the same problem as Dave (from above :)), but I fixed it a little bit different. Instead of giving BitmapFont's constructor another parameter, I retrieve the fontfilepath like this:

m_strFilePath = System.IO.Path.GetDirectoryName(strFontFilename)+"";

Less flexible than Dave's solution, but true in most cases... I guess :)

Anyway, thanks!
Anonymous
September 03, 2006
Thanks David and Thijs (Gloei) for the comments and feedback. I'll be fixing the directory problem in the next release (which should be in a day or two).
Anonymous
September 04, 2006
System.Xml apparently doesn't exist. I have only installed C# Express and GSE.

Is this something that comes with VS 2005 and not C# Express?

How do I get System.Xml installed? [System.Xml is part of the .Net Framework but you need to add a reference to it in your project to get things to compile.

To add a reference to it, right-click on the "References" folder in your project and select "Add Reference". From the .NET tab, find and select System.Xml and click the "OK" button to add it.

I'll be updating the docs to include this information. -GaryKac]
Anonymous
September 11, 2006
How does one dispose of an instance of this class before a GraphicsDevice.Reset() call?

I'm getting ***[4036] Direct3D9: (ERROR) :All user created D3DPOOL_DEFAULT surfaces must be freed before Reset can succeed. Reset Fails. *** when I try to reset the device for a resolution change.

If I remove "MyFont.drawString(...)" from my Draw() routine the exception goes away so I'm guessing that the surface created can't be disposed if MyFont hasn't been disposed yet.

TIA,

Matt [I just answered this at http://blogs.msdn.com/garykac/archive/2006/08/30/728521.aspx#comments. Basically, you need to dispose of the SpriteBatch and the Textures before resetting. Actually, what I should say is that "I should have provided a Dispose method that disposes of the SpriteBatch and the Textures for you". I'll fix this for the next version, but in the meantime you can write a Dispose method for BitmapFont that cleans things up properly. The code to do this is given at the post linked to above. Sorry! -GaryKac]
Anonymous
September 16, 2006
PingBack from http://blogs.msdn.com/garykac/articles/749188.aspx

Freigeben über

Creating Bitmap Fonts using bmfontgen

Introduction

Features

Limitations

I : Basic Operation

Using BMFontGen to create fonts

Using bitmap fonts created by BMFontGen in XNA

II : Advanced Options

Choosing an appropriate text rendering hint

Using an options file

Extended options

Adding custom glyphs to a font

Creating fonts with international characters

Creating CJK fonts

Appendix A
Summary of available options

-blackbg

-bmsize size

-bold

-custom ch file x y w h base aw lsb fw

-fontdialog

-italic

-listfonts

-listfontsfile fontfilename

-name fontname

-nowarn-all

-nowarn-missingglyph

-optfile filename

-output base-output-name

-range start-end

-size size

-source filename

-strikeout

-trh hint

-underline

-v

Comments

Zusätzliche Ressourcen

Freigeben über

Creating Bitmap Fonts using bmfontgen

Introduction

Features

Limitations

I : Basic Operation

Using BMFontGen to create fonts

Using bitmap fonts created by BMFontGen in XNA

II : Advanced Options

Choosing an appropriate text rendering hint

Using an options file

Extended options

Adding custom glyphs to a font

Creating fonts with international characters

Creating CJK fonts

Appendix ASummary of available options

-blackbg

-bmsize size

-bold

-custom ch file x y w h base aw lsb fw

-fontdialog

-italic

-listfonts

-listfontsfile fontfilename

-name fontname

-nowarn-all

-nowarn-missingglyph

-optfile filename

-output base-output-name

-range start-end

-size size

-source filename

-strikeout

-trh hint

-underline

-v

Comments

Zusätzliche Ressourcen

Appendix A
Summary of available options