Text and fonts

1. TCastleFont class

To draw some text you need an instance of the TCastleFont class. To make it easy, one global instance of this class is already created for you: UIFont (part of CastleControls unit). So you can simply draw text like this:

UIFont.Print(10, 10, Yellow, 'Some text to print');

You should place such drawing code inside a render method, for example inside the OnRender event of TCastleWindowCustom or OnRender event of TCastleControlCustom or inside the overridden TUIControl.Render implementation. See the manual about 2D drawing for a general info about 2D rendering.

Instead of directly drawing the text, you can also use TCastleLabel that manages the drawing for you. You can customize it's font using CustomFont, FontSize and SmallFont properties. Many other UI controls (see for example unit CastleControls) descend from TUIControlFont. and thus may have their font customized, for example TCastleButton.

TCastleFont class has a lot of methods and properties.

2. Create a new font

TCastleFont is actually an abstract class representing some font that can be drawn. To create a new font, you create an instance of a non-abstract class, most often the TTextureFont class — it draws font glyphs from a texture, and can be loaded from a TTF font. There are other possible font implementations, for example TSimpleTextureFont allows to use a font drawn on an image (so you can make colorful letters, with fancy custom outline and such).

See castle_game_engine/examples/fonts/font_from_texture.lpr for a simple example of creating fonts. In the basic version, you simply use TTextureFont constructor to load a font from a TTF file (or any other font format supported by the FreeType2 library). So you construct a font like this:

MyNewFont := TTextureFont.Create(ApplicationData('MyFontFile.ttf'), 20, true);

Remember to install the FreeType2 library for this to work. On Windows, place appropriate FreeType2 DLL alongside the exe, you can get the DLL from castle_game_engine/tools/build-tool/data/external_libraries/ directory of the engine.

Note that you can also assign the new font as the global UIFont, so it will be by default used by all standard UI controls:

UIFont := TTextureFont.Create(ApplicationData('MyFontFile.ttf'), 20, true);

Instead of loading the font data from a TTF file, you can also provide a TTextureFontData instance to the TTextureFont constructor. This allows to create the font data at runtime or to use the font data embedded in a Pascal source code. You can use the texture-font-to-pascal program (compile it from castle_game_engine/tools/texture-font-to-pascal/texture-font-to-pascal.lpr) to convert a TTF file into a Pascal unit:

texture-font-to-pascal --size 20 MyFontFile.ttf

In response, it will create a unit called CastleTextureFont_MyFontFile_20 with a public function:

function TextureFont_MyFontFile_20: TTextureFontData;

You can use this unit in your program, and create a font instance like this:

MyNewFont := TTextureFont.Create(TextureFont_MyFontFile_20);

The advantages of embedding a font inside a Pascal unit are:

  • You don't need to distribute the FreeType2 library. This is especially useful when developing for Android or iOS or web plugin, when linking with an additional library can be troublesome.
  • Font is loaded slightly faster, since it's already processed to a suitable texture data.

The disadvantages are of course that you cannot easily edit the TTF anymore, you will need to rerun the texture-font-to-pascal command and recompile your program to see the new font.

3. International characters

All font routines (printing, measuring) expect the international characters to be encoded using UTF-8. To draw the international characters (anything beyond basic English ASCII set) you also need to create a font with these characters.

When constructing TTextureFont, you need to use the overloaded constructor with parameter ACharacters (TUnicodeCharList). Provide there a list of the characters (including all the possible international characters) that you want to display. Like this:

uses ..., CasteFonts, CastleStringUtils, CastleUnicode;
 
function CreateMyFont: TCastleFont;
var
  Characters: TUnicodeCharList;
begin
  Characters := TUnicodeCharList.Create;
  try
    Characters.Add(SimpleAsciiCharacters);
    Characters.Add('string containing all my weird chars, in UTF-8:)');
    Result := TTextureFont.Create(ApplicationData('MyFontFile.ttf'), 20, true,
      Characters);
  finally FreeAndNil(Characters) end;
end;

If you use texture-font-to-pascal utility to embed fonts in Pascal sources then just use it's parameter --sample-text to provide the additional (beyond simple ASCII) chars. Like this:

texture-font-to-pascal --size 20 MyFontFile.ttf --sample-text 'string containing all my weird chars, in UTF-8:)'

Note that you need to make sure to provide the sample characters encoded in UTF-8. Make sure your source code is in UTF-8 (edit it using an UTF-8 capable editor, consider adding an UTF-8 BOM, consider using {$CODEPAGE UTF8}, see FPC source codepage option). If you use texture-font-to-pascal then make sure that your command-line, and/or your script interpreter, correcly handle UTF-8 (on Linux, this should be a breeze, since everything works with UTF-8 out of the box; on modern Windows it should also work).