ref: 7bab6ae3e901e282dda489fd34136b65690b0062
dir: /include/freetype/ftlcdfil.h/
/***************************************************************************/
/* */
/* ftlcdfil.h */
/* */
/* FreeType API for color filtering of subpixel bitmap glyphs */
/* (specification). */
/* */
/* Copyright 2006 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
FT_BEGIN_HEADER
/****************************************************************************
*
* @func:
* FT_LcdFilter
*
* @description:
* a list of values used to identify various types of LCD filters
*
* @values:
* FT_LCD_FILTER_NONE :: value 0 means do not perform filtering. when
* used with subpixel rendering, this will result in sometimes severe
* color fringes
*
* FT_LCD_FILTER_DEFAULT ::
* the default filter reduces color fringes considerably, at the cost of
* a slight bluriness in the output
*
* FT_LCD_FILTER_LIGHT ::
* the light filter is a variant that produces less bluriness
* at the cost of slightly more color fringes than the default one. It
* might be better than the default one, depending on your monitor and
* personal vision.
*
* FT_LCD_FILTER_LEGACY ::
* this filter corresponds to the original libXft color filter, this
* provides high contrast output, but can exhibit really bad color fringes
* if your glyphs are not extremely well hinted to the pixel grid. In
* other words, it only works well when enabling the TrueType bytecode
* interpreter *and* using high-quality hinted fonts. It will suck for
* all other cases.
*
* this filter is only provided for comparison purposes, and might be
* disabled/unsupported in the future...
*/
typedef enum
{
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_weights ::
* A pointer to an array of 5 bytes corresponding to the weights of a
* 5-tap FIR filter. Each weight must be positive, and their sum
* should be at least 256 to avoid loss of darkness in the rendered
* glyphs. The sum can be greater than 256 to darken the glyphs
* (`el-cheapo gamma').
*
* 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_weights' 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 the library.
*
* The filter affects glyph bitmaps rendered through FT_Render_Glyph,
* @@FT_Glyph_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.
*
*/
FT_EXPORT( FT_Error )
FT_Library_SetLcdFilter( FT_Library library,
FT_LcdFilter filter );
/* */
FT_END_HEADER
#endif /* __FT_LCD_FILTER_H__ */
/* END */