FreeType » Docs » Support API » Glyph Stroker

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Glyph Stroker

Synopsis

This component generates stroked outlines of a given vectorial glyph. It also allows you to retrieve the ‘outside’ and/or the ‘inside’ borders of the stroke.

This can be useful to generate ‘bordered’ glyph, i.e., glyphs displayed with a colored (and anti-aliased) border around their shape.

FT_Stroker

Defined in FT_STROKER_H (freetype/ftstroke.h).

  typedef struct FT_StrokerRec_*  FT_Stroker;

Opaque handle to a path stroker object.

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FT_Stroker_LineJoin

Defined in FT_STROKER_H (freetype/ftstroke.h).

  typedef enum  FT_Stroker_LineJoin_
  {
    FT_STROKER_LINEJOIN_ROUND          = 0,
    FT_STROKER_LINEJOIN_BEVEL          = 1,
    FT_STROKER_LINEJOIN_MITER_VARIABLE = 2,
    FT_STROKER_LINEJOIN_MITER          = FT_STROKER_LINEJOIN_MITER_VARIABLE,
    FT_STROKER_LINEJOIN_MITER_FIXED    = 3

  } FT_Stroker_LineJoin;

These values determine how two joining lines are rendered in a stroker.

values

FT_STROKER_LINEJOIN_ROUND	Used to render rounded line joins. Circular arcs are used to join two lines smoothly.
FT_STROKER_LINEJOIN_BEVEL	Used to render beveled line joins. The outer corner of the joined lines is filled by enclosing the triangular region of the corner with a straight line between the outer corners of each stroke.
FT_STROKER_LINEJOIN_MITER_FIXED	Used to render mitered line joins, with fixed bevels if the miter limit is exceeded. The outer edges of the strokes for the two segments are extended until they meet at an angle. A bevel join (see above) is used if the segments meet at too sharp an angle and the outer edges meet beyond a distance corresponding to the meter limit. This prevents long spikes being created. FT_STROKER_LINEJOIN_MITER_FIXED generates a miter line join as used in PostScript and PDF.
FT_STROKER_LINEJOIN_MITER_VARIABLE
FT_STROKER_LINEJOIN_MITER	Used to render mitered line joins, with variable bevels if the miter limit is exceeded. The intersection of the strokes is clipped perpendicularly to the bisector, at a distance corresponding to the miter limit. This prevents long spikes being created. FT_STROKER_LINEJOIN_MITER_VARIABLE generates a mitered line join as used in XPS. FT_STROKER_LINEJOIN_MITER is an alias for FT_STROKER_LINEJOIN_MITER_VARIABLE, retained for backward compatibility.

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FT_Stroker_LineCap

Defined in FT_STROKER_H (freetype/ftstroke.h).

  typedef enum  FT_Stroker_LineCap_
  {
    FT_STROKER_LINECAP_BUTT = 0,
    FT_STROKER_LINECAP_ROUND,
    FT_STROKER_LINECAP_SQUARE

  } FT_Stroker_LineCap;

These values determine how the end of opened sub-paths are rendered in a stroke.

values

FT_STROKER_LINECAP_BUTT	The end of lines is rendered as a full stop on the last point itself.
FT_STROKER_LINECAP_ROUND	The end of lines is rendered as a half-circle around the last point.
FT_STROKER_LINECAP_SQUARE	The end of lines is rendered as a square around the last point.

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FT_StrokerBorder

Defined in FT_STROKER_H (freetype/ftstroke.h).

  typedef enum  FT_StrokerBorder_
  {
    FT_STROKER_BORDER_LEFT = 0,
    FT_STROKER_BORDER_RIGHT

  } FT_StrokerBorder;

These values are used to select a given stroke border in FT_Stroker_GetBorderCounts and FT_Stroker_ExportBorder.

values

FT_STROKER_BORDER_LEFT	Select the left border, relative to the drawing direction.
FT_STROKER_BORDER_RIGHT	Select the right border, relative to the drawing direction.

note

Applications are generally interested in the ‘inside’ and ‘outside’ borders. However, there is no direct mapping between these and the ‘left’ and ‘right’ ones, since this really depends on the glyph's drawing orientation, which varies between font formats.

You can however use FT_Outline_GetInsideBorder and FT_Outline_GetOutsideBorder to get these.

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FT_Outline_GetInsideBorder

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_StrokerBorder )
  FT_Outline_GetInsideBorder( FT_Outline*  outline );

Retrieve the FT_StrokerBorder value corresponding to the ‘inside’ borders of a given outline.

input

outline

The source outline handle.

return

The border index. FT_STROKER_BORDER_RIGHT for empty or invalid outlines.

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FT_Outline_GetOutsideBorder

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_StrokerBorder )
  FT_Outline_GetOutsideBorder( FT_Outline*  outline );

Retrieve the FT_StrokerBorder value corresponding to the ‘outside’ borders of a given outline.

input

outline

The source outline handle.

return

The border index. FT_STROKER_BORDER_LEFT for empty or invalid outlines.

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FT_Glyph_Stroke

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Glyph_Stroke( FT_Glyph    *pglyph,
                   FT_Stroker   stroker,
                   FT_Bool      destroy );

Stroke a given outline glyph object with a given stroker.

inout

pglyph

Source glyph handle on input, new glyph handle on output.

input

stroker	A stroker handle.
destroy	A Boolean. If 1, the source glyph object is destroyed on success.

return

FreeType error code. 0 means success.

note

The source glyph is untouched in case of error.

Adding stroke may yield a significantly wider and taller glyph depending on how large of a radius was used to stroke the glyph. You may need to manually adjust horizontal and vertical advance amounts to account for this added size.

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FT_Glyph_StrokeBorder

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Glyph_StrokeBorder( FT_Glyph    *pglyph,
                         FT_Stroker   stroker,
                         FT_Bool      inside,
                         FT_Bool      destroy );

Stroke a given outline glyph object with a given stroker, but only return either its inside or outside border.

inout

pglyph

Source glyph handle on input, new glyph handle on output.

input

stroker	A stroker handle.
inside	A Boolean. If 1, return the inside border, otherwise the outside border.
destroy	A Boolean. If 1, the source glyph object is destroyed on success.

return

FreeType error code. 0 means success.

note

The source glyph is untouched in case of error.

Adding stroke may yield a significantly wider and taller glyph depending on how large of a radius was used to stroke the glyph. You may need to manually adjust horizontal and vertical advance amounts to account for this added size.

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FT_Stroker_New

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_New( FT_Library   library,
                  FT_Stroker  *astroker );

Create a new stroker object.

input

library

FreeType library handle.

output

astroker

A new stroker object handle. NULL in case of error.

return

FreeType error code. 0 means success.

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FT_Stroker_Set

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( void )
  FT_Stroker_Set( FT_Stroker           stroker,
                  FT_Fixed             radius,
                  FT_Stroker_LineCap   line_cap,
                  FT_Stroker_LineJoin  line_join,
                  FT_Fixed             miter_limit );

Reset a stroker object's attributes.

input

stroker	The target stroker handle.
radius	The border radius.
line_cap	The line cap style.
line_join	The line join style.
miter_limit	The maximum reciprocal sine of half-angle at the miter join, expressed as 16.16 fixed-point value.

note

The radius is expressed in the same units as the outline coordinates.

The miter_limit multiplied by the radius gives the maximum size of a miter spike, at which it is clipped for FT_STROKER_LINEJOIN_MITER_VARIABLE or replaced with a bevel join for FT_STROKER_LINEJOIN_MITER_FIXED.

This function calls FT_Stroker_Rewind automatically.

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FT_Stroker_Rewind

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( void )
  FT_Stroker_Rewind( FT_Stroker  stroker );

Reset a stroker object without changing its attributes. You should call this function before beginning a new series of calls to FT_Stroker_BeginSubPath or FT_Stroker_EndSubPath.

input

stroker

The target stroker handle.

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FT_Stroker_ParseOutline

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_ParseOutline( FT_Stroker   stroker,
                           FT_Outline*  outline,
                           FT_Bool      opened );

A convenience function used to parse a whole outline with the stroker. The resulting outline(s) can be retrieved later by functions like FT_Stroker_GetCounts and FT_Stroker_Export.

input

stroker	The target stroker handle.
outline	The source outline.
opened	A boolean. If 1, the outline is treated as an open path instead of a closed one.

return

FreeType error code. 0 means success.

note

If opened is 0 (the default), the outline is treated as a closed path, and the stroker generates two distinct ‘border’ outlines.

If opened is 1, the outline is processed as an open path, and the stroker generates a single ‘stroke’ outline.

This function calls FT_Stroker_Rewind automatically.

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FT_Stroker_Done

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( void )
  FT_Stroker_Done( FT_Stroker  stroker );

Destroy a stroker object.

input

stroker

A stroker handle. Can be NULL.

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FT_Stroker_BeginSubPath

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_BeginSubPath( FT_Stroker  stroker,
                           FT_Vector*  to,
                           FT_Bool     open );

Start a new sub-path in the stroker.

input

stroker	The target stroker handle.
to	A pointer to the start vector.
open	A boolean. If 1, the sub-path is treated as an open one.

return

FreeType error code. 0 means success.

note

This function is useful when you need to stroke a path that is not stored as an FT_Outline object.

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FT_Stroker_EndSubPath

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_EndSubPath( FT_Stroker  stroker );

Close the current sub-path in the stroker.

input

stroker

The target stroker handle.

return

FreeType error code. 0 means success.

note

You should call this function after FT_Stroker_BeginSubPath. If the subpath was not ‘opened’, this function ‘draws’ a single line segment to the start position when needed.

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FT_Stroker_LineTo

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_LineTo( FT_Stroker  stroker,
                     FT_Vector*  to );

‘Draw’ a single line segment in the stroker's current sub-path, from the last position.

input

stroker	The target stroker handle.
to	A pointer to the destination point.

return

FreeType error code. 0 means success.

note

You should call this function between FT_Stroker_BeginSubPath and FT_Stroker_EndSubPath.

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FT_Stroker_ConicTo

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_ConicTo( FT_Stroker  stroker,
                      FT_Vector*  control,
                      FT_Vector*  to );

‘Draw’ a single quadratic Bezier in the stroker's current sub-path, from the last position.

input

stroker	The target stroker handle.
control	A pointer to a Bezier control point.
to	A pointer to the destination point.

return

FreeType error code. 0 means success.

note

You should call this function between FT_Stroker_BeginSubPath and FT_Stroker_EndSubPath.

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FT_Stroker_CubicTo

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_CubicTo( FT_Stroker  stroker,
                      FT_Vector*  control1,
                      FT_Vector*  control2,
                      FT_Vector*  to );

‘Draw’ a single cubic Bezier in the stroker's current sub-path, from the last position.

input

stroker	The target stroker handle.
control1	A pointer to the first Bezier control point.
control2	A pointer to second Bezier control point.
to	A pointer to the destination point.

return

FreeType error code. 0 means success.

note

You should call this function between FT_Stroker_BeginSubPath and FT_Stroker_EndSubPath.

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FT_Stroker_GetBorderCounts

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_GetBorderCounts( FT_Stroker        stroker,
                              FT_StrokerBorder  border,
                              FT_UInt          *anum_points,
                              FT_UInt          *anum_contours );

Call this function once you have finished parsing your paths with the stroker. It returns the number of points and contours necessary to export one of the ‘border’ or ‘stroke’ outlines generated by the stroker.

input

stroker	The target stroker handle.
border	The border index.

output

anum_points	The number of points.
anum_contours	The number of contours.

return

FreeType error code. 0 means success.

note

When an outline, or a sub-path, is ‘closed’, the stroker generates two independent ‘border’ outlines, named ‘left’ and ‘right’.

When the outline, or a sub-path, is ‘opened’, the stroker merges the ‘border’ outlines with caps. The ‘left’ border receives all points, while the ‘right’ border becomes empty.

Use the function FT_Stroker_GetCounts instead if you want to retrieve the counts associated to both borders.

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FT_Stroker_ExportBorder

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( void )
  FT_Stroker_ExportBorder( FT_Stroker        stroker,
                           FT_StrokerBorder  border,
                           FT_Outline*       outline );

Call this function after FT_Stroker_GetBorderCounts to export the corresponding border to your own FT_Outline structure.

Note that this function appends the border points and contours to your outline, but does not try to resize its arrays.

input

stroker	The target stroker handle.
border	The border index.
outline	The target outline handle.

note

Always call this function after FT_Stroker_GetBorderCounts to get sure that there is enough room in your FT_Outline object to receive all new data.

When an outline, or a sub-path, is ‘closed’, the stroker generates two independent ‘border’ outlines, named ‘left’ and ‘right’.

When the outline, or a sub-path, is ‘opened’, the stroker merges the ‘border’ outlines with caps. The ‘left’ border receives all points, while the ‘right’ border becomes empty.

Use the function FT_Stroker_Export instead if you want to retrieve all borders at once.

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FT_Stroker_GetCounts

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( FT_Error )
  FT_Stroker_GetCounts( FT_Stroker  stroker,
                        FT_UInt    *anum_points,
                        FT_UInt    *anum_contours );

Call this function once you have finished parsing your paths with the stroker. It returns the number of points and contours necessary to export all points/borders from the stroked outline/path.

input

stroker

The target stroker handle.

output

anum_points	The number of points.
anum_contours	The number of contours.

return

FreeType error code. 0 means success.

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FT_Stroker_Export

Defined in FT_STROKER_H (freetype/ftstroke.h).

  FT_EXPORT( void )
  FT_Stroker_Export( FT_Stroker   stroker,
                     FT_Outline*  outline );

Call this function after FT_Stroker_GetBorderCounts to export all borders to your own FT_Outline structure.

Note that this function appends the border points and contours to your outline, but does not try to resize its arrays.

input

stroker	The target stroker handle.
outline	The target outline handle.

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