Werner Lemberg
19 years ago
parent
9b15ea341c
commit
2c002e13a7
8 changed files with 268 additions and 188 deletions
@ -1,89 +1,125 @@ |
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/***************************************************************************/ |
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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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* @func: 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 :: handle to target library instance |
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* |
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* filter_weights :: a pointer to an array of 5 bytes corresponding |
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* to the weights of a 5-tap FIR filter. Each |
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* weight must be positive, and their sum should |
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* be at least 256 to avoid loss of darkness |
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* in the rendered glyphs. The sum can be greater |
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* than 256 to darken the glyphs (el-cheapo gamma) |
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* |
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* you can use @FT_LCD_FILTER_NONE here to disable |
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* this feature, or @FT_LCD_FILTER_DEFAULT to use |
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* a default filter that should work well on most |
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* LCD screens. |
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* |
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* @return: |
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* 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 will |
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* not do anything except return @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 |
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* to all default builds of the library |
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* |
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* the filter affects glyph bitmaps rendered through |
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* @FT_Render_Glyph, @FT_Glyph_Get_Bitmap, @FT_Load_Glyph and |
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* @FT_Load_Char. |
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* |
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* It does *not* affect the output of @FT_Outline_Render |
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* and @FT_Outline_Get_Bitmap. |
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* |
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* if this feature is activated, the dimensions of LCD glyph bitmaps |
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* will be either larger or taller than the dimensions of the corresponding |
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* outline with regards to the pixel grid. For example, for @FT_RENDER_MODE_LCD, |
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* the filter adds up to 3 pixels to the left, and 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 need |
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* to modify thei layout / glyph positioning code when enabling the filter. |
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*/ |
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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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* @enum: FT_LCD_FILTER_XXX |
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* |
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* @desc: a list of constants correspond to useful lcd filter settings to |
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* be used when calling @FT_Library_SetLcdFilter |
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* |
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* @values: |
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* FT_LCD_FILTER_NONE :: the value NULL is reserved to indicate that |
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* LCD color filtering 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 |
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* should work well on most LCD screen. For the really curious, |
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* it corresponds to the array 0x10, 0x40, 0x70, 0x40, 0x10 |
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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_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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