FreeType » Docs » Format-Specific API » Gasp Table

Gasp Table¶

Synopsis¶

The function FT_Get_Gasp can be used to query a TrueType or OpenType font for specific entries in its ‘gasp’ table, if any. This is mainly useful when implementing native TrueType hinting with the bytecode interpreter to duplicate the Windows text rendering results.

FT_GASP_XXX¶

Defined in FT_GASP_H (freetype/ftgasp.h).

#define FT_GASP_NO_TABLE               -1
#define FT_GASP_DO_GRIDFIT           0x01
#define FT_GASP_DO_GRAY              0x02
#define FT_GASP_SYMMETRIC_GRIDFIT    0x04
#define FT_GASP_SYMMETRIC_SMOOTHING  0x08

A list of values and/or bit-flags returned by the FT_Get_Gasp function.

values

FT_GASP_NO_TABLE	This special value means that there is no GASP table in this face. It is up to the client to decide what to do.
FT_GASP_DO_GRIDFIT	Grid-fitting and hinting should be performed at the specified ppem. This really means TrueType bytecode interpretation. If this bit is not set, no hinting gets applied.
FT_GASP_DO_GRAY	Anti-aliased rendering should be performed at the specified ppem. If not set, do monochrome rendering.
FT_GASP_SYMMETRIC_SMOOTHING	If set, smoothing along multiple axes must be used with ClearType.
FT_GASP_SYMMETRIC_GRIDFIT	Grid-fitting must be used with ClearType's symmetric smoothing.

note

The bit-flags FT_GASP_DO_GRIDFIT and FT_GASP_DO_GRAY are to be used for standard font rasterization only. Independently of that, FT_GASP_SYMMETRIC_SMOOTHING and FT_GASP_SYMMETRIC_GRIDFIT are to be used if ClearType is enabled (and FT_GASP_DO_GRIDFIT and FT_GASP_DO_GRAY are consequently ignored).

‘ClearType’ is Microsoft's implementation of LCD rendering, partly protected by patents.

since

2.3.0

FT_Get_Gasp¶

Defined in FT_GASP_H (freetype/ftgasp.h).

  FT_EXPORT( FT_Int )
  FT_Get_Gasp( FT_Face  face,
               FT_UInt  ppem );

For a TrueType or OpenType font file, return the rasterizer behaviour flags from the font's ‘gasp’ table corresponding to a given character pixel size.

input

face	The source face handle.
ppem	The vertical character pixel size.

return

Bit flags (see FT_GASP_XXX), or FT_GASP_NO_TABLE if there is no ‘gasp’ table in the face.

note

If you want to use the MM functionality of OpenType variation fonts (i.e., using FT_Set_Var_Design_Coordinates and friends), call this function after setting an instance since the return values can change.

since

2.3.0