126 lines
4.7 KiB
C
126 lines
4.7 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 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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FT_BEGIN_HEADER
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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_weights ::
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* A pointer to an array of 5 bytes corresponding to the weights of a
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* 5-tap FIR filter. Each weight must be positive, and their sum
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* should be at least 256 to avoid loss of darkness in the rendered
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* glyphs. The sum can be greater than 256 to darken the glyphs
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* (`el-cheapo gamma').
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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_weights' value other
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* than @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 the library.
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*
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* The filter affects glyph bitmaps rendered through FT_Render_Glyph,
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* @@FT_Glyph_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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*/
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FT_EXPORT( FT_Error )
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FT_Library_SetLcdFilter( FT_Library library,
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const FT_Byte* filter_weights );
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/**************************************************************************
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*
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* @enum:
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* FT_LCD_FILTER_XXX
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*
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* @description:
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* A list of constants which correspond to useful lcd filter settings
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* for the @FT_Library_SetLcdFilter function.
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*
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* @values:
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* FT_LCD_FILTER_NONE ::
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* The value NULL is reserved to indicate that LCD color filtering
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* should be disabled.
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*
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* FT_LCD_FILTER_DEFAULT ::
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* This value is reserved to indicate a default FIR filter that should
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* work well on most LCD screen. It corresponds to the array 0x10,
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* 0x40, 0x70, 0x40, 0x10.
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*
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*/
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#define FT_LCD_FILTER_NONE ( (const FT_Byte*)NULL )
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#define FT_LCD_FILTER_DEFAULT ( (const FT_Byte*)(void*)(ft_ptrdiff_t)1 )
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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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