freetype2/include/freetype/ftstroke.h

/****************************************************************************
 *
 * ftstroke.h
 *
 *   FreeType path stroker (specification).
 *
 * Copyright (C) 2002-2019 by
 * David Turner, Robert Wilhelm, and Werner Lemberg.
 *
 * This file is part of the FreeType project, and may only be used,
 * modified, and distributed under the terms of the FreeType project
 * license, LICENSE.TXT.  By continuing to use, modify, or distribute
 * this file you indicate that you have read the license and
 * understand and accept it fully.
 *
 */


#ifndef FTSTROKE_H_
#define FTSTROKE_H_

#include <ft2build.h>
#include FT_OUTLINE_H
#include FT_GLYPH_H


FT_BEGIN_HEADER


  /**************************************************************************
   *
   * @section:
   *    glyph_stroker
   *
   * @title:
   *    Glyph Stroker
   *
   * @abstract:
   *    Generating bordered and stroked glyphs.
   *
   * @description:
   *    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 coloured (and anti-aliased) border around their
   *    shape.
   *
   * @order:
   *    FT_Stroker
   *
   *    FT_Stroker_LineJoin
   *    FT_Stroker_LineCap
   *    FT_StrokerBorder
   *
   *    FT_Outline_GetInsideBorder
   *    FT_Outline_GetOutsideBorder
   *
   *    FT_Glyph_Stroke
   *    FT_Glyph_StrokeBorder
   *
   *    FT_Stroker_New
   *    FT_Stroker_Set
   *    FT_Stroker_Rewind
   *    FT_Stroker_ParseOutline
   *    FT_Stroker_Done
   *
   *    FT_Stroker_BeginSubPath
   *    FT_Stroker_EndSubPath
   *
   *    FT_Stroker_LineTo
   *    FT_Stroker_ConicTo
   *    FT_Stroker_CubicTo
   *
   *    FT_Stroker_GetBorderCounts
   *    FT_Stroker_ExportBorder
   *    FT_Stroker_GetCounts
   *    FT_Stroker_Export
   *
   */


  /**************************************************************************
   *
   * @type:
   *   FT_Stroker
   *
   * @description:
   *   Opaque handle to a path stroker object.
   */
  typedef struct FT_StrokerRec_*  FT_Stroker;


  /**************************************************************************
   *
   * @enum:
   *   FT_Stroker_LineJoin
   *
   * @description:
   *   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.  If the segments
   *     meet at too sharp an angle (such that the miter would extend from
   *     the intersection of the segments a distance greater than the product
   *     of the miter limit value and the border radius), then a bevel join
   *     (see above) is used instead.  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 at a
   *     line perpendicular to the bisector of the angle between the strokes,
   *     at the distance from the intersection of the segments equal to the
   *     product of the miter limit value and the border radius.  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.
   */
  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;


  /**************************************************************************
   *
   * @enum:
   *   FT_Stroker_LineCap
   *
   * @description:
   *   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.
   */
  typedef enum  FT_Stroker_LineCap_
  {
    FT_STROKER_LINECAP_BUTT = 0,
    FT_STROKER_LINECAP_ROUND,
    FT_STROKER_LINECAP_SQUARE

  } FT_Stroker_LineCap;


  /**************************************************************************
   *
   * @enum:
   *   FT_StrokerBorder
   *
   * @description:
   *   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.
   */
  typedef enum  FT_StrokerBorder_
  {
    FT_STROKER_BORDER_LEFT = 0,
    FT_STROKER_BORDER_RIGHT

  } FT_StrokerBorder;


  /**************************************************************************
   *
   * @function:
   *   FT_Outline_GetInsideBorder
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_StrokerBorder )
  FT_Outline_GetInsideBorder( FT_Outline*  outline );


  /**************************************************************************
   *
   * @function:
   *   FT_Outline_GetOutsideBorder
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_StrokerBorder )
  FT_Outline_GetOutsideBorder( FT_Outline*  outline );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_New
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_New( FT_Library   library,
                  FT_Stroker  *astroker );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_Set
   *
   * @description:
   *   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 miter limit for the `FT_STROKER_LINEJOIN_MITER_FIXED` and
   *     `FT_STROKER_LINEJOIN_MITER_VARIABLE` line join styles, expressed as
   *     16.16 fixed-point value.
   *
   * @note:
   *   The radius is expressed in the same units as the outline coordinates.
   *
   *   This function calls @FT_Stroker_Rewind automatically.
   */
  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 );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_Rewind
   *
   * @description:
   *   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.
   */
  FT_EXPORT( void )
  FT_Stroker_Rewind( FT_Stroker  stroker );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_ParseOutline
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_ParseOutline( FT_Stroker   stroker,
                           FT_Outline*  outline,
                           FT_Bool      opened );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_BeginSubPath
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_BeginSubPath( FT_Stroker  stroker,
                           FT_Vector*  to,
                           FT_Bool     open );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_EndSubPath
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_EndSubPath( FT_Stroker  stroker );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_LineTo
   *
   * @description:
   *   '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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_LineTo( FT_Stroker  stroker,
                     FT_Vector*  to );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_ConicTo
   *
   * @description:
   *   '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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_ConicTo( FT_Stroker  stroker,
                      FT_Vector*  control,
                      FT_Vector*  to );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_CubicTo
   *
   * @description:
   *   '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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_CubicTo( FT_Stroker  stroker,
                      FT_Vector*  control1,
                      FT_Vector*  control2,
                      FT_Vector*  to );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_GetBorderCounts
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_GetBorderCounts( FT_Stroker        stroker,
                              FT_StrokerBorder  border,
                              FT_UInt          *anum_points,
                              FT_UInt          *anum_contours );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_ExportBorder
   *
   * @description:
   *   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.
   */
  FT_EXPORT( void )
  FT_Stroker_ExportBorder( FT_Stroker        stroker,
                           FT_StrokerBorder  border,
                           FT_Outline*       outline );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_GetCounts
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Stroker_GetCounts( FT_Stroker  stroker,
                        FT_UInt    *anum_points,
                        FT_UInt    *anum_contours );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_Export
   *
   * @description:
   *   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.
   */
  FT_EXPORT( void )
  FT_Stroker_Export( FT_Stroker   stroker,
                     FT_Outline*  outline );


  /**************************************************************************
   *
   * @function:
   *   FT_Stroker_Done
   *
   * @description:
   *   Destroy a stroker object.
   *
   * @input:
   *   stroker ::
   *     A stroker handle.  Can be `NULL`.
   */
  FT_EXPORT( void )
  FT_Stroker_Done( FT_Stroker  stroker );


  /**************************************************************************
   *
   * @function:
   *   FT_Glyph_Stroke
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Glyph_Stroke( FT_Glyph    *pglyph,
                   FT_Stroker   stroker,
                   FT_Bool      destroy );


  /**************************************************************************
   *
   * @function:
   *   FT_Glyph_StrokeBorder
   *
   * @description:
   *   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.
   */
  FT_EXPORT( FT_Error )
  FT_Glyph_StrokeBorder( FT_Glyph    *pglyph,
                         FT_Stroker   stroker,
                         FT_Bool      inside,
                         FT_Bool      destroy );

  /* */

FT_END_HEADER

#endif /* FTSTROKE_H_ */


/* END */


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