90 lines
3.3 KiB
C
90 lines
3.3 KiB
C
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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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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_END_HEADER
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#endif /* __FT_LCD_FILTER_H__ */
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