FreeType » Docs » Extended API » Glyph Management

Glyph Management¶

Synopsis¶

This section contains definitions used to manage glyph data through generic FT_Glyph objects. Each of them can contain a bitmap, a vector outline, or even images in other formats. These objects are detached from FT_Face, contrary to FT_GlyphSlot.

FT_Glyph¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct FT_GlyphRec_*  FT_Glyph;

Handle to an object used to model generic glyph images. It is a pointer to the FT_GlyphRec structure and can contain a glyph bitmap or pointer.

note

Glyph objects are not owned by the library. You must thus release them manually (through FT_Done_Glyph) before calling FT_Done_FreeType.

FT_GlyphRec¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct  FT_GlyphRec_
  {
    FT_Library             library;
    const FT_Glyph_Class*  clazz;
    FT_Glyph_Format        format;
    FT_Vector              advance;

  } FT_GlyphRec;

The root glyph structure contains a given glyph image plus its advance width in 16.16 fixed-point format.

fields

library	A handle to the FreeType library object.
clazz	A pointer to the glyph's class. Private.
format	The format of the glyph's image.
advance	A 16.16 vector that gives the glyph's advance width.

FT_BitmapGlyph¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct FT_BitmapGlyphRec_*  FT_BitmapGlyph;

A handle to an object used to model a bitmap glyph image. This is a ‘sub-class’ of FT_Glyph, and a pointer to FT_BitmapGlyphRec.

FT_BitmapGlyphRec¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct  FT_BitmapGlyphRec_
  {
    FT_GlyphRec  root;
    FT_Int       left;
    FT_Int       top;
    FT_Bitmap    bitmap;

  } FT_BitmapGlyphRec;

A structure used for bitmap glyph images. This really is a ‘sub-class’ of FT_GlyphRec.

fields

root	The root fields of `FT_Glyph`.
left	The left-side bearing, i.e., the horizontal distance from the current pen position to the left border of the glyph bitmap.
top	The top-side bearing, i.e., the vertical distance from the current pen position to the top border of the glyph bitmap. This distance is positive for upwards y!
bitmap	A descriptor for the bitmap.

note

You can typecast an FT_Glyph to FT_BitmapGlyph if you have glyph->format == FT_GLYPH_FORMAT_BITMAP. This lets you access the bitmap's contents easily.

The corresponding pixel buffer is always owned by FT_BitmapGlyph and is thus created and destroyed with it.

FT_OutlineGlyph¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct FT_OutlineGlyphRec_*  FT_OutlineGlyph;

A handle to an object used to model an outline glyph image. This is a ‘sub-class’ of FT_Glyph, and a pointer to FT_OutlineGlyphRec.

FT_OutlineGlyphRec¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct  FT_OutlineGlyphRec_
  {
    FT_GlyphRec  root;
    FT_Outline   outline;

  } FT_OutlineGlyphRec;

A structure used for outline (vectorial) glyph images. This really is a ‘sub-class’ of FT_GlyphRec.

fields

root	The root `FT_Glyph` fields.
outline	A descriptor for the outline.

note

You can typecast an FT_Glyph to FT_OutlineGlyph if you have glyph->format == FT_GLYPH_FORMAT_OUTLINE. This lets you access the outline's content easily.

As the outline is extracted from a glyph slot, its coordinates are expressed normally in 26.6 pixels, unless the flag FT_LOAD_NO_SCALE was used in FT_Load_Glyph or FT_Load_Char.

The outline's tables are always owned by the object and are destroyed with it.

FT_SvgGlyph¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct FT_SvgGlyphRec_*  FT_SvgGlyph;

A handle to an object used to model an SVG glyph. This is a ‘sub-class’ of FT_Glyph, and a pointer to FT_SvgGlyphRec.

since

2.12

FT_SvgGlyphRec¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef struct  FT_SvgGlyphRec_
  {
    FT_GlyphRec  root;

    FT_Byte*  svg_document;
    FT_ULong  svg_document_length;

    FT_UInt  glyph_index;

    FT_Size_Metrics  metrics;
    FT_UShort        units_per_EM;

    FT_UShort  start_glyph_id;
    FT_UShort  end_glyph_id;

    FT_Matrix  transform;
    FT_Vector  delta;

  } FT_SvgGlyphRec;

A structure used for OT-SVG glyphs. This is a ‘sub-class’ of FT_GlyphRec.

fields

root	The root `FT_GlyphRec` fields.
svg_document	A pointer to the SVG document.
svg_document_length	The length of `svg_document`.
glyph_index	The index of the glyph to be rendered.
metrics	A metrics object storing the size information.
units_per_EM	The size of the EM square.
start_glyph_id	The first glyph ID in the glyph range covered by this document.
end_glyph_id	The last glyph ID in the glyph range covered by this document.
transform	A 2x2 transformation matrix to apply to the glyph while rendering it.
delta	Translation to apply to the glyph while rendering.

note

The Glyph Management API requires FT_Glyph or its ‘sub-class’ to have all the information needed to completely define the glyph's rendering. Outline-based glyphs can directly apply transformations to the outline but this is not possible for an SVG document that hasn't been parsed. Therefore, the transformation is stored along with the document. In the absence of a ‘ViewBox’ or ‘Width’/'Height' attribute, the size of the ViewPort should be assumed to be ‘units_per_EM’.

FT_New_Glyph¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  FT_EXPORT( FT_Error )
  FT_New_Glyph( FT_Library       library,
                FT_Glyph_Format  format,
                FT_Glyph         *aglyph );

A function used to create a new empty glyph image. Note that the created FT_Glyph object must be released with FT_Done_Glyph.

input

library	A handle to the FreeType library object.
format	The format of the glyph's image.

output

aglyph

A handle to the glyph object.

return

FreeType error code. 0 means success.

since

2.10

FT_Get_Glyph¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  FT_EXPORT( FT_Error )
  FT_Get_Glyph( FT_GlyphSlot  slot,
                FT_Glyph     *aglyph );

A function used to extract a glyph image from a slot. Note that the created FT_Glyph object must be released with FT_Done_Glyph.

input

slot	A handle to the source glyph slot.

output

aglyph

A handle to the glyph object. NULL in case of error.

return

FreeType error code. 0 means success.

note

Because *aglyph->advance.x and *aglyph->advance.y are 16.16 fixed-point numbers, slot->advance.x and slot->advance.y (which are in 26.6 fixed-point format) must be in the range ]-32768;32768[.

FT_Glyph_Copy¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  FT_EXPORT( FT_Error )
  FT_Glyph_Copy( FT_Glyph   source,
                 FT_Glyph  *target );

A function used to copy a glyph image. Note that the created FT_Glyph object must be released with FT_Done_Glyph.

input

source

A handle to the source glyph object.

output

target

A handle to the target glyph object. NULL in case of error.

return

FreeType error code. 0 means success.

FT_Glyph_Transform¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  FT_EXPORT( FT_Error )
  FT_Glyph_Transform( FT_Glyph          glyph,
                      const FT_Matrix*  matrix,
                      const FT_Vector*  delta );

Transform a glyph image if its format is scalable.

inout

glyph

A handle to the target glyph object.

input

matrix	A pointer to a 2x2 matrix to apply.
delta	A pointer to a 2d vector to apply. Coordinates are expressed in 1/64 of a pixel.

return

FreeType error code (if not 0, the glyph format is not scalable).

note

The 2x2 transformation matrix is also applied to the glyph's advance vector.

FT_Glyph_BBox_Mode¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  typedef enum  FT_Glyph_BBox_Mode_
  {
    FT_GLYPH_BBOX_UNSCALED  = 0,
    FT_GLYPH_BBOX_SUBPIXELS = 0,
    FT_GLYPH_BBOX_GRIDFIT   = 1,
    FT_GLYPH_BBOX_TRUNCATE  = 2,
    FT_GLYPH_BBOX_PIXELS    = 3

  } FT_Glyph_BBox_Mode;


  /* these constants are deprecated; use the corresponding */
  /* `FT_Glyph_BBox_Mode` values instead                   */
#define ft_glyph_bbox_unscaled   FT_GLYPH_BBOX_UNSCALED
#define ft_glyph_bbox_subpixels  FT_GLYPH_BBOX_SUBPIXELS
#define ft_glyph_bbox_gridfit    FT_GLYPH_BBOX_GRIDFIT
#define ft_glyph_bbox_truncate   FT_GLYPH_BBOX_TRUNCATE
#define ft_glyph_bbox_pixels     FT_GLYPH_BBOX_PIXELS

The mode how the values of FT_Glyph_Get_CBox are returned.

values

FT_GLYPH_BBOX_UNSCALED	Return unscaled font units.
FT_GLYPH_BBOX_SUBPIXELS	Return unfitted 26.6 coordinates.
FT_GLYPH_BBOX_GRIDFIT	Return grid-fitted 26.6 coordinates.
FT_GLYPH_BBOX_TRUNCATE	Return coordinates in integer pixels.
FT_GLYPH_BBOX_PIXELS	Return grid-fitted pixel coordinates.

FT_Glyph_Get_CBox¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  FT_EXPORT( void )
  FT_Glyph_Get_CBox( FT_Glyph  glyph,
                     FT_UInt   bbox_mode,
                     FT_BBox  *acbox );

Return a glyph's ‘control box’. The control box encloses all the outline's points, including Bezier control points. Though it coincides with the exact bounding box for most glyphs, it can be slightly larger in some situations (like when rotating an outline that contains Bezier outside arcs).

Computing the control box is very fast, while getting the bounding box can take much more time as it needs to walk over all segments and arcs in the outline. To get the latter, you can use the ‘ftbbox’ component, which is dedicated to this single task.

input

glyph	A handle to the source glyph object.
mode	The mode that indicates how to interpret the returned bounding box values.

output

acbox

The glyph coordinate bounding box. Coordinates are expressed in 1/64 of pixels if it is grid-fitted.

note

Coordinates are relative to the glyph origin, using the y upwards convention.

If the glyph has been loaded with FT_LOAD_NO_SCALE, bbox_mode must be set to FT_GLYPH_BBOX_UNSCALED to get unscaled font units in 26.6 pixel format. The value FT_GLYPH_BBOX_SUBPIXELS is another name for this constant.

If the font is tricky and the glyph has been loaded with FT_LOAD_NO_SCALE, the resulting CBox is meaningless. To get reasonable values for the CBox it is necessary to load the glyph at a large ppem value (so that the hinting instructions can properly shift and scale the subglyphs), then extracting the CBox, which can be eventually converted back to font units.

Note that the maximum coordinates are exclusive, which means that one can compute the width and height of the glyph image (be it in integer or 26.6 pixels) as:

  width  = bbox.xMax - bbox.xMin;
  height = bbox.yMax - bbox.yMin;

Note also that for 26.6 coordinates, if bbox_mode is set to FT_GLYPH_BBOX_GRIDFIT, the coordinates will also be grid-fitted, which corresponds to:

  bbox.xMin = FLOOR(bbox.xMin);
  bbox.yMin = FLOOR(bbox.yMin);
  bbox.xMax = CEILING(bbox.xMax);
  bbox.yMax = CEILING(bbox.yMax);

To get the bbox in pixel coordinates, set bbox_mode to FT_GLYPH_BBOX_TRUNCATE.

To get the bbox in grid-fitted pixel coordinates, set bbox_mode to FT_GLYPH_BBOX_PIXELS.

FT_Glyph_To_Bitmap¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  FT_EXPORT( FT_Error )
  FT_Glyph_To_Bitmap( FT_Glyph*         the_glyph,
                      FT_Render_Mode    render_mode,
                      const FT_Vector*  origin,
                      FT_Bool           destroy );

Convert a given glyph object to a bitmap glyph object.

inout

the_glyph

A pointer to a handle to the target glyph.

input

render_mode	An enumeration that describes how the data is rendered.
origin	A pointer to a vector used to translate the glyph image before rendering. Can be 0 (if no translation). The origin is expressed in 26.6 pixels.
destroy	A boolean that indicates that the original glyph image should be destroyed by this function. It is never destroyed in case of error.

return

FreeType error code. 0 means success.

note

This function does nothing if the glyph format isn't scalable.

The glyph image is translated with the origin vector before rendering.

The first parameter is a pointer to an FT_Glyph handle that will be replaced by this function (with newly allocated data). Typically, you would do something like the following (omitting error handling).

  FT_Glyph        glyph;
  FT_BitmapGlyph  glyph_bitmap;


  // load glyph
  error = FT_Load_Char( face, glyph_index, FT_LOAD_DEFAULT );

  // extract glyph image
  error = FT_Get_Glyph( face->glyph, &glyph );

  // convert to a bitmap (default render mode + destroying old)
  if ( glyph->format != FT_GLYPH_FORMAT_BITMAP )
  {
    error = FT_Glyph_To_Bitmap( &glyph, FT_RENDER_MODE_NORMAL,
                                0, 1 );
    if ( error ) // `glyph' unchanged
      ...
  }

  // access bitmap content by typecasting
  glyph_bitmap = (FT_BitmapGlyph)glyph;

  // do funny stuff with it, like blitting/drawing
  ...

  // discard glyph image (bitmap or not)
  FT_Done_Glyph( glyph );

Here is another example, again without error handling.

  FT_Glyph  glyphs[MAX_GLYPHS]


  ...

  for ( idx = 0; i < MAX_GLYPHS; i++ )
    error = FT_Load_Glyph( face, idx, FT_LOAD_DEFAULT ) ||
            FT_Get_Glyph ( face->glyph, &glyphs[idx] );

  ...

  for ( idx = 0; i < MAX_GLYPHS; i++ )
  {
    FT_Glyph  bitmap = glyphs[idx];


    ...

    // after this call, `bitmap' no longer points into
    // the `glyphs' array (and the old value isn't destroyed)
    FT_Glyph_To_Bitmap( &bitmap, FT_RENDER_MODE_MONO, 0, 0 );

    ...

    FT_Done_Glyph( bitmap );
  }

  ...

  for ( idx = 0; i < MAX_GLYPHS; i++ )
    FT_Done_Glyph( glyphs[idx] );

FT_Done_Glyph¶

Defined in FT_GLYPH_H (freetype/ftglyph.h).

  FT_EXPORT( void )
  FT_Done_Glyph( FT_Glyph  glyph );

Destroy a given glyph.

input

glyph

A handle to the target glyph object. Can be NULL.