/src/compiler/android-ndk/jni/freetype/include/freetype/ftlcdfil.h

  1/***************************************************************************/
  2/*                                                                         */
  3/*  ftlcdfil.h                                                             */
  4/*                                                                         */
  5/*    FreeType API for color filtering of subpixel bitmap glyphs           */
  6/*    (specification).                                                     */
  7/*                                                                         */
  8/*  Copyright 2006, 2007, 2008 by                                          */
  9/*  David Turner, Robert Wilhelm, and Werner Lemberg.                      */
 10/*                                                                         */
 11/*  This file is part of the FreeType project, and may only be used,       */
 12/*  modified, and distributed under the terms of the FreeType project      */
 13/*  license, LICENSE.TXT.  By continuing to use, modify, or distribute     */
 14/*  this file you indicate that you have read the license and              */
 15/*  understand and accept it fully.                                        */
 16/*                                                                         */
 17/***************************************************************************/
 18
 19
 20#ifndef __FT_LCD_FILTER_H__
 21#define __FT_LCD_FILTER_H__
 22
 23#include <ft2build.h>
 24#include FT_FREETYPE_H
 25
 26#ifdef FREETYPE_H
 27#error "freetype.h of FreeType 1 has been loaded!"
 28#error "Please fix the directory search order for header files"
 29#error "so that freetype.h of FreeType 2 is found first."
 30#endif
 31
 32
 33FT_BEGIN_HEADER
 34
 35  /***************************************************************************
 36   *
 37   * @section:
 38   *   lcd_filtering
 39   *
 40   * @title:
 41   *   LCD Filtering
 42   *
 43   * @abstract:
 44   *   Reduce color fringes of LCD-optimized bitmaps.
 45   *
 46   * @description:
 47   *   The @FT_Library_SetLcdFilter API can be used to specify a low-pass
 48   *   filter which is then applied to LCD-optimized bitmaps generated
 49   *   through @FT_Render_Glyph.  This is useful to reduce color fringes
 50   *   which would occur with unfiltered rendering.
 51   *
 52   *   Note that no filter is active by default, and that this function is
 53   *   *not* implemented in default builds of the library.  You need to
 54   *   #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your `ftoption.h' file
 55   *   in order to activate it.
 56   */
 57
 58
 59  /****************************************************************************
 60   *
 61   * @func:
 62   *   FT_LcdFilter
 63   *
 64   * @description:
 65   *   A list of values to identify various types of LCD filters.
 66   *
 67   * @values:
 68   *   FT_LCD_FILTER_NONE ::
 69   *     Do not perform filtering.  When used with subpixel rendering, this
 70   *     results in sometimes severe color fringes.
 71   *
 72   *   FT_LCD_FILTER_DEFAULT ::
 73   *     The default filter reduces color fringes considerably, at the cost
 74   *     of a slight blurriness in the output.
 75   *
 76   *   FT_LCD_FILTER_LIGHT ::
 77   *     The light filter is a variant that produces less blurriness at the
 78   *     cost of slightly more color fringes than the default one.  It might
 79   *     be better, depending on taste, your monitor, or your personal vision.
 80   *
 81   *   FT_LCD_FILTER_LEGACY ::
 82   *     This filter corresponds to the original libXft color filter.  It
 83   *     provides high contrast output but can exhibit really bad color
 84   *     fringes if glyphs are not extremely well hinted to the pixel grid.
 85   *     In other words, it only works well if the TrueType bytecode
 86   *     interpreter is enabled *and* high-quality hinted fonts are used.
 87   *
 88   *     This filter is only provided for comparison purposes, and might be
 89   *     disabled or stay unsupported in the future.
 90   *
 91   * @since:
 92   *   2.3.0
 93   */
 94  typedef enum  FT_LcdFilter_
 95  {
 96    FT_LCD_FILTER_NONE    = 0,
 97    FT_LCD_FILTER_DEFAULT = 1,
 98    FT_LCD_FILTER_LIGHT   = 2,
 99    FT_LCD_FILTER_LEGACY  = 16,
100
101    FT_LCD_FILTER_MAX   /* do not remove */
102
103  } FT_LcdFilter;
104
105
106  /**************************************************************************
107   *
108   * @func:
109   *   FT_Library_SetLcdFilter
110   *
111   * @description:
112   *   This function is used to apply color filtering to LCD decimated
113   *   bitmaps, like the ones used when calling @FT_Render_Glyph with
114   *   @FT_RENDER_MODE_LCD or @FT_RENDER_MODE_LCD_V.
115   *
116   * @input:
117   *   library ::
118   *     A handle to the target library instance.
119   *
120   *   filter ::
121   *     The filter type.
122   *
123   *     You can use @FT_LCD_FILTER_NONE here to disable this feature, or
124   *     @FT_LCD_FILTER_DEFAULT to use a default filter that should work
125   *     well on most LCD screens.
126   *
127   * @return:
128   *   FreeType error code.  0~means success.
129   *
130   * @note:
131   *   This feature is always disabled by default.  Clients must make an
132   *   explicit call to this function with a `filter' value other than
133   *   @FT_LCD_FILTER_NONE in order to enable it.
134   *
135   *   Due to *PATENTS* covering subpixel rendering, this function doesn't
136   *   do anything except returning `FT_Err_Unimplemented_Feature' if the
137   *   configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not
138   *   defined in your build of the library, which should correspond to all
139   *   default builds of FreeType.
140   *
141   *   The filter affects glyph bitmaps rendered through @FT_Render_Glyph,
142   *   @FT_Outline_Get_Bitmap, @FT_Load_Glyph, and @FT_Load_Char.
143   *
144   *   It does _not_ affect the output of @FT_Outline_Render and
145   *   @FT_Outline_Get_Bitmap.
146   *
147   *   If this feature is activated, the dimensions of LCD glyph bitmaps are
148   *   either larger or taller than the dimensions of the corresponding
149   *   outline with regards to the pixel grid.  For example, for
150   *   @FT_RENDER_MODE_LCD, the filter adds up to 3~pixels to the left, and
151   *   up to 3~pixels to the right.
152   *
153   *   The bitmap offset values are adjusted correctly, so clients shouldn't
154   *   need to modify their layout and glyph positioning code when enabling
155   *   the filter.
156   *
157   * @since:
158   *   2.3.0
159   */
160  FT_EXPORT( FT_Error )
161  FT_Library_SetLcdFilter( FT_Library    library,
162                           FT_LcdFilter  filter );
163
164  /* */
165
166
167FT_END_HEADER
168
169#endif /* __FT_LCD_FILTER_H__ */
170
171
172/* END */