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/***************************************************************************/
/* */
/* 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_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,
const FT_Byte* filter_weights );
/**************************************************************************
*
* @enum:
* FT_LCD_FILTER_XXX
*
* @description:
* A list of constants which correspond to useful lcd filter settings
* for the @FT_Library_SetLcdFilter function.
*
* @values:
* FT_LCD_FILTER_NONE ::
* The value NULL is reserved to indicate that LCD color filtering
* should be disabled.
*
* FT_LCD_FILTER_DEFAULT ::
* This value is reserved to indicate a default FIR filter that should
* work well on most LCD screen. It corresponds to the array 0x10,
* 0x40, 0x70, 0x40, 0x10.
*
*/
#define FT_LCD_FILTER_NONE ( (const FT_Byte*)NULL )
#define FT_LCD_FILTER_DEFAULT ( (const FT_Byte*)(void*)(ft_ptrdiff_t)1 )
/* */
FT_END_HEADER
#endif /* __FT_LCD_FILTER_H__ */
/* END */
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