/***************************************************************************/

/*                                                                         */

/*  ftlcdfil.h                                                             */

/*                                                                         */

/*    FreeType API for color filtering of subpixel bitmap glyphs           */

/*    (specification).                                                     */

/*                                                                         */

/*  Copyright 2006, 2007, 2008, 2010 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 __FT_LCD_FILTER_H__

#define __FT_LCD_FILTER_H__



#include <ft2build.h>

#include FT_FREETYPE_H



#ifdef FREETYPE_H

#error "freetype.h of FreeType 1 has been loaded!"

#error "Please fix the directory search order for header files"

#error "so that freetype.h of FreeType 2 is found first."

#endif





FT_BEGIN_HEADER



  /***************************************************************************

   *

   * @section:

   *   lcd_filtering

   *

   * @title:

   *   LCD Filtering

   *

   * @abstract:

   *   Reduce color fringes of LCD-optimized bitmaps.

   *

   * @description:

   *   The @FT_Library_SetLcdFilter API can be used to specify a low-pass

   *   filter which is then applied to LCD-optimized bitmaps generated

   *   through @FT_Render_Glyph.  This is useful to reduce color fringes

   *   which would occur with unfiltered rendering.

   *

   *   Note that no filter is active by default, and that this function is

   *   *not* implemented in default builds of the library.  You need to

   *   #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your `ftoption.h' file

   *   in order to activate it.

   */





  /****************************************************************************

   *

   * @enum:

   *   FT_LcdFilter

   *

   * @description:

   *   A list of values to identify various types of LCD filters.

   *

   * @values:

   *   FT_LCD_FILTER_NONE ::

   *     Do not perform filtering.  When used with subpixel rendering, this

   *     results in sometimes severe color fringes.

   *

   *   FT_LCD_FILTER_DEFAULT ::

   *     The default filter reduces color fringes considerably, at the cost

   *     of a slight blurriness in the output.

   *

   *   FT_LCD_FILTER_LIGHT ::

   *     The light filter is a variant that produces less blurriness at the

   *     cost of slightly more color fringes than the default one.  It might

   *     be better, depending on taste, your monitor, or your personal vision.

   *

   *   FT_LCD_FILTER_LEGACY ::

   *     This filter corresponds to the original libXft color filter.  It

   *     provides high contrast output but can exhibit really bad color

   *     fringes if glyphs are not extremely well hinted to the pixel grid.

   *     In other words, it only works well if the TrueType bytecode

   *     interpreter is enabled *and* high-quality hinted fonts are used.

   *

   *     This filter is only provided for comparison purposes, and might be

   *     disabled or stay unsupported in the future.

   *

   * @since:

   *   2.3.0

   */

  typedef enum  FT_LcdFilter_

  {

    FT_LCD_FILTER_NONE    = 0,

    FT_LCD_FILTER_DEFAULT = 1,

    FT_LCD_FILTER_LIGHT   = 2,

    FT_LCD_FILTER_LEGACY  = 16,



    FT_LCD_FILTER_MAX   /* do not remove */



  } FT_LcdFilter;





  /**************************************************************************

   *

   * @func:

   *   FT_Library_SetLcdFilter

   *

   * @description:

   *   This function is used to apply color filtering to LCD decimated

   *   bitmaps, like the ones used when calling @FT_Render_Glyph with

   *   @FT_RENDER_MODE_LCD or @FT_RENDER_MODE_LCD_V.

   *

   * @input:

   *   library ::

   *     A handle to the target library instance.

   *

   *   filter ::

   *     The filter type.

   *

   *     You can use @FT_LCD_FILTER_NONE here to disable this feature, or

   *     @FT_LCD_FILTER_DEFAULT to use a default filter that should work

   *     well on most LCD screens.

   *

   * @return:

   *   FreeType error code.  0~means success.

   *

   * @note:

   *   This feature is always disabled by default.  Clients must make an

   *   explicit call to this function with a `filter' value other than

   *   @FT_LCD_FILTER_NONE in order to enable it.

   *

   *   Due to *PATENTS* covering subpixel rendering, this function doesn't

   *   do anything except returning `FT_Err_Unimplemented_Feature' if the

   *   configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not

   *   defined in your build of the library, which should correspond to all

   *   default builds of FreeType.

   *

   *   The filter affects glyph bitmaps rendered through @FT_Render_Glyph,

   *   @FT_Outline_Get_Bitmap, @FT_Load_Glyph, and @FT_Load_Char.

   *

   *   It does _not_ affect the output of @FT_Outline_Render and

   *   @FT_Outline_Get_Bitmap.

   *

   *   If this feature is activated, the dimensions of LCD glyph bitmaps are

   *   either larger or taller than the dimensions of the corresponding

   *   outline with regards to the pixel grid.  For example, for

   *   @FT_RENDER_MODE_LCD, the filter adds up to 3~pixels to the left, and

   *   up to 3~pixels to the right.

   *

   *   The bitmap offset values are adjusted correctly, so clients shouldn't

   *   need to modify their layout and glyph positioning code when enabling

   *   the filter.

   *

   * @since:

   *   2.3.0

   */

  FT_EXPORT( FT_Error )

  FT_Library_SetLcdFilter( FT_Library    library,

                           FT_LcdFilter  filter );





  /**************************************************************************

   *

   * @func:

   *   FT_Library_SetLcdFilterWeights

   *

   * @description:

   *   Use this function to override the filter weights selected by

   *   @FT_Library_SetLcdFilter.  By default, FreeType uses the quintuple

   *   (0x00, 0x55, 0x56, 0x55, 0x00) for FT_LCD_FILTER_LIGHT, and (0x10,

   *   0x40, 0x70, 0x40, 0x10) for FT_LCD_FILTER_DEFAULT and

   *   FT_LCD_FILTER_LEGACY.

   *

   * @input:

   *   library ::

   *     A handle to the target library instance.

   *

   *   weights ::

   *     A pointer to an array; the function copies the first five bytes and

   *     uses them to specify the filter weights.

   *

   * @return:

   *   FreeType error code.  0~means success.

   *

   * @note:

   *   Due to *PATENTS* covering subpixel rendering, this function doesn't

   *   do anything except returning `FT_Err_Unimplemented_Feature' if the

   *   configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not

   *   defined in your build of the library, which should correspond to all

   *   default builds of FreeType.

   *

   *   This function must be called after @FT_Library_SetLcdFilter to have

   *   any effect.

   *

   * @since:

   *   2.4.0

   */

  FT_EXPORT( FT_Error )

  FT_Library_SetLcdFilterWeights( FT_Library      library,

                                  unsigned char  *weights );



  /* */





FT_END_HEADER



#endif /* __FT_LCD_FILTER_H__ */





/* END */

