forked from minhngoc25a/freetype2
214 lines
7.5 KiB
C
214 lines
7.5 KiB
C
/***************************************************************************/
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/* */
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/* ftlcdfil.h */
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/* */
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/* FreeType API for color filtering of subpixel bitmap glyphs */
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/* (specification). */
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/* */
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/* Copyright 2006, 2007, 2008, 2010 by */
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/* David Turner, Robert Wilhelm, and Werner Lemberg. */
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/* */
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/* This file is part of the FreeType project, and may only be used, */
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/* modified, and distributed under the terms of the FreeType project */
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/* license, LICENSE.TXT. By continuing to use, modify, or distribute */
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/* this file you indicate that you have read the license and */
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/* understand and accept it fully. */
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/* */
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/***************************************************************************/
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#ifndef __FT_LCD_FILTER_H__
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#define __FT_LCD_FILTER_H__
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#include <ft2build.h>
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#include FT_FREETYPE_H
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#ifdef FREETYPE_H
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#error "freetype.h of FreeType 1 has been loaded!"
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#error "Please fix the directory search order for header files"
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#error "so that freetype.h of FreeType 2 is found first."
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#endif
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FT_BEGIN_HEADER
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/***************************************************************************
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*
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* @section:
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* lcd_filtering
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*
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* @title:
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* LCD Filtering
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*
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* @abstract:
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* Reduce color fringes of LCD-optimized bitmaps.
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*
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* @description:
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* The @FT_Library_SetLcdFilter API can be used to specify a low-pass
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* filter which is then applied to LCD-optimized bitmaps generated
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* through @FT_Render_Glyph. This is useful to reduce color fringes
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* which would occur with unfiltered rendering.
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*
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* Note that no filter is active by default, and that this function is
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* *not* implemented in default builds of the library. You need to
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* #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your `ftoption.h' file
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* in order to activate it.
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*/
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/****************************************************************************
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*
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* @func:
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* FT_LcdFilter
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*
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* @description:
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* A list of values to identify various types of LCD filters.
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*
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* @values:
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* FT_LCD_FILTER_NONE ::
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* Do not perform filtering. When used with subpixel rendering, this
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* results in sometimes severe color fringes.
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*
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* FT_LCD_FILTER_DEFAULT ::
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* The default filter reduces color fringes considerably, at the cost
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* of a slight blurriness in the output.
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*
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* FT_LCD_FILTER_LIGHT ::
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* The light filter is a variant that produces less blurriness at the
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* cost of slightly more color fringes than the default one. It might
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* be better, depending on taste, your monitor, or your personal vision.
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*
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* FT_LCD_FILTER_LEGACY ::
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* This filter corresponds to the original libXft color filter. It
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* provides high contrast output but can exhibit really bad color
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* fringes if glyphs are not extremely well hinted to the pixel grid.
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* In other words, it only works well if the TrueType bytecode
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* interpreter is enabled *and* high-quality hinted fonts are used.
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*
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* This filter is only provided for comparison purposes, and might be
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* disabled or stay unsupported in the future.
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*
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* @since:
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* 2.3.0
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*/
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typedef enum FT_LcdFilter_
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{
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FT_LCD_FILTER_NONE = 0,
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FT_LCD_FILTER_DEFAULT = 1,
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FT_LCD_FILTER_LIGHT = 2,
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FT_LCD_FILTER_LEGACY = 16,
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FT_LCD_FILTER_MAX /* do not remove */
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} FT_LcdFilter;
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/**************************************************************************
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*
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* @func:
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* FT_Library_SetLcdFilter
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*
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* @description:
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* This function is used to apply color filtering to LCD decimated
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* bitmaps, like the ones used when calling @FT_Render_Glyph with
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* @FT_RENDER_MODE_LCD or @FT_RENDER_MODE_LCD_V.
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*
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* @input:
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* library ::
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* A handle to the target library instance.
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*
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* filter ::
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* The filter type.
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*
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* You can use @FT_LCD_FILTER_NONE here to disable this feature, or
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* @FT_LCD_FILTER_DEFAULT to use a default filter that should work
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* well on most LCD screens.
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*
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* @return:
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* FreeType error code. 0~means success.
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*
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* @note:
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* This feature is always disabled by default. Clients must make an
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* explicit call to this function with a `filter' value other than
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* @FT_LCD_FILTER_NONE in order to enable it.
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*
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* Due to *PATENTS* covering subpixel rendering, this function doesn't
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* do anything except returning `FT_Err_Unimplemented_Feature' if the
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* configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not
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* defined in your build of the library, which should correspond to all
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* default builds of FreeType.
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*
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* The filter affects glyph bitmaps rendered through @FT_Render_Glyph,
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* @FT_Outline_Get_Bitmap, @FT_Load_Glyph, and @FT_Load_Char.
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*
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* It does _not_ affect the output of @FT_Outline_Render and
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* @FT_Outline_Get_Bitmap.
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*
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* If this feature is activated, the dimensions of LCD glyph bitmaps are
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* either larger or taller than the dimensions of the corresponding
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* outline with regards to the pixel grid. For example, for
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* @FT_RENDER_MODE_LCD, the filter adds up to 3~pixels to the left, and
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* up to 3~pixels to the right.
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*
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* The bitmap offset values are adjusted correctly, so clients shouldn't
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* need to modify their layout and glyph positioning code when enabling
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* the filter.
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*
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* @since:
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* 2.3.0
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*/
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FT_EXPORT( FT_Error )
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FT_Library_SetLcdFilter( FT_Library library,
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FT_LcdFilter filter );
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/**************************************************************************
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*
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* @func:
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* FT_Library_SetLcdFilterWeights
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*
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* @description:
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* Use this function to override the filter weights selected by
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* @FT_Library_SetLcdFilter. By default, FreeType uses the quintuple
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* (0x00, 0x55, 0x56, 0x55, 0x00) for FT_LCD_FILTER_LIGHT, and (0x10,
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* 0x40, 0x70, 0x40, 0x10) for FT_LCD_FILTER_DEFAULT and
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* FT_LCD_FILTER_LEGACY.
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*
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* @input:
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* library ::
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* A handle to the target library instance.
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*
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* weights ::
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* A pointer to an array; the function copies the first five bytes and
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* uses them to specify the filter weights.
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*
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* @return:
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* FreeType error code. 0~means success.
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*
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* @note:
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* Due to *PATENTS* covering subpixel rendering, this function doesn't
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* do anything except returning `FT_Err_Unimplemented_Feature' if the
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* configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not
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* defined in your build of the library, which should correspond to all
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* default builds of FreeType.
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*
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* This function must be called after @FT_Library_SetLcdFilter to have
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* any effect.
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*
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* @since:
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* 2.3.13
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*/
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FT_EXPORT( FT_Error )
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FT_Library_SetLcdFilterWeights( FT_Library library,
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unsigned char *weights );
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/* */
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FT_END_HEADER
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#endif /* __FT_LCD_FILTER_H__ */
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/* END */
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