What is FreeType?

FreeType is the industry-standard open-source font rendering engine, used in virtually every major computing platform. It loads and decodes font files in every common format — TrueType (TTF), OpenType (OTF), WOFF, Type 1, CFF, PCF, and more — and renders individual glyphs to pixel bitmaps with high-quality anti-aliasing.

At small sizes, FreeType's hinting engine snaps glyph outlines to the pixel grid so characters remain crisp and readable. At larger sizes it produces smooth, sub-pixel-accurate outlines. Three hinting strategies are available: TrueType native bytecode hints (best for screen text), FreeType's own auto-hinter (good for OpenType/CFF), and no hinting (best for large sizes or subpixel rendering).

FreeType powers Android, Chrome, Firefox, the entire Linux desktop stack (GTK, Qt, Pango, Cairo), LibreOffice, SDL2_ttf, and many embedded systems. It is the de-facto standard for anything that draws text.

Font Rendering Pipeline

Every glyph goes through the same sequence of steps:

FreeType uses 26.6 fixed-point format for glyph metrics (multiply by 64 to get real pixels). The advance width tells you how far to move the pen after drawing a glyph; the bearing is the offset from the pen position to the glyph's bounding box.

Types

Code Example — Render “Hello” Glyph by Glyph

uses freetype;

var
  Lib     : TFTLibrary;
  Face    : TFTFace;
  Bmp     : TFTBitmap;
  Metrics : TFTGlyphMetrics;
  C       : Char;

begin
  Lib  := InitLibrary;
  Face := NewFace(Lib, '/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf', 0);
  SetPixelSize(Face, 0, 32);  { 0 = auto width, 32 = height in pixels }

  for C in 'Hello' do begin
    LoadChar(Face, Ord(C));       { GetGlyphIndex + LoadGlyph in one call }
    RenderGlyph(Face, rmNormal);  { 8-bit grayscale anti-aliased }
    Bmp     := GetBitmap(Face);
    Metrics := GetMetrics(Face);
    { Bmp.Data holds Bmp.Rows * Bmp.Pitch bytes of grayscale pixel data }
    { Pen advance (pixels) = Metrics.HoriAdvance div 64 }
    { blit Bmp.Data to your screen surface at the current pen position }
  end;

  FreeFace(Face);
  FreeLibrary(Lib);
end.

API Reference

Library

Function	Description
InitLibrary(): TFTLibrary	Initialize the FreeType library. Call once per process.
FreeLibrary(Lib)	Release the library and all associated resources.
FreeTypeVersion(): string	Return the linked FreeType version string (e.g. "2.13.2").

Face (font file)

Function	Description
NewFace(Lib, Path, FaceIndex): TFTFace	Load a font face from a file path. FaceIndex 0 = first face.
NewFaceMemory(Lib, Data, FaceIndex): TFTFace	Load a font face from an in-memory byte string.
FreeFace(Face)	Release a font face handle.
GetFaceInfo(Face): TFTFaceInfo	Return family name, style, glyph count, line metrics, flags.

Size Selection

Function	Description
SetPixelSize(Face, Width, Height)	Set rendering size in pixels. Pass 0 for Width to auto-compute from height.
SetCharSize(Face, WidthPt, HeightPt, HorizDPI, VertDPI)	Set size in points at a given DPI (typically 72 or 96). Use for print-quality output.

Glyph Rendering

Function	Description
GetGlyphIndex(Face, Codepoint): Integer	Map a Unicode codepoint to a glyph index. Returns 0 if not in font.
LoadGlyph(Face, GlyphIndex)	Load a glyph by its index into the glyph slot.
LoadChar(Face, Codepoint)	Convenience: GetGlyphIndex + LoadGlyph in one call.
RenderGlyph(Face, Mode)	Render the loaded glyph to a bitmap using the given TFTRenderMode.
GetBitmap(Face): TFTBitmap	Return the rendered bitmap from the glyph slot.
GetMetrics(Face): TFTGlyphMetrics	Return advance width, bearing, and bounding box (26.6 fixed-point).

Kerning

Function	Description
GetKerning(Face, LeftGlyph, RightGlyph): TFTKerning	Return the kerning adjustment (X, Y) between two adjacent glyph indices. Both indices must come from GetGlyphIndex.

Text Metrics & Convenience

Function	Description
MeasureText(Face, Text): Integer	Return the total advance width of a UTF-8 string in pixels.
GetTextBounds(Face, Text; out Width, Height)	Return bounding box dimensions of a UTF-8 string.
RenderText(Face, Text): TFTBitmap	Render a full UTF-8 string to an 8-bit grayscale bitmap in one call.
RenderTextRGBA(Face, Text, R, G, B): TFTBitmap	Render a UTF-8 string to an RGBA bitmap with the given color, ready for direct alpha-blending onto a surface.