godot/thirdparty/freetype/src/sdf/ftsdfcommon.c

/****************************************************************************
 *
 * ftsdfcommon.c
 *
 *   Auxiliary data for Signed Distance Field support (body).
 *
 * Copyright (C) 2020-2023 by
 * David Turner, Robert Wilhelm, and Werner Lemberg.
 *
 * Written by Anuj Verma.
 *
 * 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.
 *
 */


#include "ftsdf.h"
#include "ftsdfcommon.h"


  /**************************************************************************
   *
   * common functions
   *
   */

  /*
   * Original algorithm:
   *
   *   https://github.com/chmike/fpsqrt
   *
   * Use this to compute the square root of a 16.16 fixed-point number.
   */
  FT_LOCAL_DEF( FT_16D16 )
  square_root( FT_16D16  val )
  { … }


  /**************************************************************************
   *
   * format and sign manipulating functions
   *
   */

  /*
   * Convert 16.16 fixed-point values to the desired output format.
   * In this case we reduce 16.16 fixed-point values to normalized
   * 8-bit values.
   *
   * The `max_value` in the parameter is the maximum value in the
   * distance field map and is equal to the spread.  We normalize
   * the distances using this value instead of computing the maximum
   * value for the entire bitmap.
   *
   * You can use this function to map the 16.16 signed values to any
   * format required.  Do note that the output buffer is 8-bit, so only
   * use an 8-bit format for `FT_SDFFormat`, or increase the buffer size in
   * `ftsdfrend.c`.
   */
  FT_LOCAL_DEF( FT_SDFFormat )
  map_fixed_to_sdf( FT_16D16  dist,
                    FT_16D16  max_value )
  { … }


  /*
   * Invert the signed distance packed into the corresponding format.
   * So if the values are negative they will become positive in the
   * chosen format.
   *
   * [Note]: This function should only be used after converting the
   *         16.16 signed distance values to `FT_SDFFormat`.  If that
   *         conversion has not been done, then simply invert the sign
   *         and use the above function to pack the values.
   */
  FT_LOCAL_DEF( FT_SDFFormat )
  invert_sign( FT_SDFFormat  dist )
  { … }


/* END */