BMFont

BMFont, short for Bitmap Font, is both a bitmap font format and a toolset used to generate bitmap fonts for real-time rendering, especially in 2D games and applications. It works by packing glyph images into a texture atlas and providing a font descriptor that maps character codes to their glyph positions and metrics.

The typical output consists of a texture atlas (commonly PNG) containing all glyph images and a font description file (often with a .fnt extension). The descriptor can be in plain text, XML, JSON, or binary form. It lists each glyph’s source rectangle (x, y, width, height), its offset within the line (xoffset, yoffset), the xadvance, and the page index when multiple texture pages are used. It may also include kerning pairs to adjust spacing between specific character combinations.

BMFont supports multiple texture pages to accommodate large fonts or extensive glyph sets and may embed kerning data. Glyphs can be exported for a chosen character set, such as ASCII or Unicode, depending on the needs of the project. The descriptor formats differ in syntax but share the same underlying data: how to locate each glyph in the atlas and how to position it during rendering.

Usage involves drawing the appropriate glyphs from the atlas using the coordinates and metrics from the descriptor, advancing with xadvance and applying xoffset and yoffset for proper alignment. This approach provides consistent rendering across platforms and resolutions and is compatible with many 2D rendering frameworks and engines. See also bitmap font, font atlas, and TrueType font.