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API for Harmony LCD rendering. 

This introduces `FT_Library_SetLcdGeometry' for setting up arbitrary
LCD subpixel geometry including non-striped patterns.
This commit is contained in:
Alexei Podtelezhnikov 2018-04-30 00:02:33 -04:00
parent 11ffff2c91
commit d526705f5e
4 changed files with 88 additions and 12 deletions
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2
include/freetype/freetype.h
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@ -3351,7 +3351,7 @@ FT_BEGIN_HEADER
/* with subpixel-rendered glyphs to prevent color-fringing! A */
/* subpixel-rendered glyph must first be filtered with a filter that */
/* gives equal weight to the three color primaries and does not */
/* exceed a sum of 0x100, see section @lcd_filtering. Then the */
/* exceed a sum of 0x100, see section @lcd_rendering. Then the */
/* only difference to gray linear blending is that subpixel-rendered */
/* linear blending is done 3~times per pixel: red foreground subpixel */
/* to red background subpixel and so on for green and blue. */

2
include/freetype/ftchapters.h
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@ -120,7 +120,7 @@
/* gzip */
/* lzw */
/* bzip2 */
/* lcd_filtering */
/* lcd_rendering */
/* */
/***************************************************************************/

66
include/freetype/ftlcdfil.h
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@ -36,10 +36,10 @@ FT_BEGIN_HEADER
/***************************************************************************
*
* @section:
* lcd_filtering
* lcd_rendering
*
* @title:
* LCD Filtering
* LCD Rendering
*
* @abstract:
* Reduce color fringes of subpixel-rendered bitmaps.
@ -230,9 +230,10 @@ FT_BEGIN_HEADER
* @FT_LCD_FILTER_NONE in order to enable it.
*
* Due to *PATENTS* covering subpixel rendering, this function doesn't
* do anything if FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not defined
* in your build of the library, which should correspond to all default
* builds of FreeType.
* 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 FreeType.
*
* @since:
* 2.3.0
@ -264,9 +265,10 @@ FT_BEGIN_HEADER
*
* @note:
* Due to *PATENTS* covering subpixel rendering, this function doesn't
* do anything if FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not defined
* in your build of the library, which should correspond to all default
* builds of FreeType.
* 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 FreeType.
*
* LCD filter weights can also be set per face using @FT_Face_Properties
* with @FT_PARAM_TAG_LCD_FILTER_WEIGHTS.
@ -296,6 +298,54 @@ FT_BEGIN_HEADER
typedef FT_Byte FT_LcdFiveTapFilter[FT_LCD_FILTER_FIVE_TAPS];
/**************************************************************************
*
* @func:
* FT_Library_SetLcdGeometry
*
* @description:
* This function can be used to modify default positions of color
* subpixels, which controls Harmony LCD rendering.
*
* @input:
* library ::
* A handle to the target library instance.
*
* sub ::
* A pointer to an array of 3 vectors in 26.6 fractional pixel format;
* the function modifies the default values, see the note below.
*
* @return:
* FreeType error code. 0~means success.
*
* @note:
* This function does nothing and returns `FT_Err_Unimplemented_Feature'
* in the context of ClearType-style subpixel rendering when
* FT_CONFIG_OPTION_SUBPIXEL_RENDERING is defined in your build of the
* library.
*
* Subpixel geometry examples:
*
* - {{-21, 0}, {0, 0}, {21, 0}} is the default, corresponding 3 color
* stripes shifted by a third of a pixel. This could be an RGB panel.
*
* - {{21, 0}, {0, 0}, {-21, 0}} looks the same as the default but
* offers you possibility to specify that this is a BGR panel instead,
* while keeping the bitmap in the same RGB888 format.
*
* - {{0, 21}, {0, 0}, {0, -21}} is the vertical RGB, but the bitmap
* stays RGB888 as a result.
*
* - {{32, -21}, {-32, -21}, {0, 42}} is a certain PenTile arrangement.
*
* @since:
* 2.9.x
*/
FT_EXPORT( FT_Error )
FT_Library_SetLcdGeometry( FT_Library library,
FT_Vector* sub );
/* */

30
src/base/ftlcdfil.c
View File

@ -351,6 +351,16 @@
return FT_Err_Ok;
}
FT_EXPORT_DEF( FT_Error )
FT_Library_SetLcdGeometry( FT_Library library,
FT_Vector* sub )
{
FT_UNUSED( library );
FT_UNUSED( sub );
return FT_THROW( Unimplemented_Feature );
}
#else /* !FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
/* add padding to accommodate outline shifts */
@ -378,6 +388,22 @@
}
FT_EXPORT_DEF( FT_Error )
FT_Library_SetLcdGeometry( FT_Library library,
FT_Vector* sub )
{
if ( !library )
return FT_THROW( Invalid_Library_Handle );
if ( !sub )
return FT_THROW( Invalid_Argument );
ft_memcpy( library->lcd_geometry, sub, 6 * sizeof( FT_Vector ) );
return FT_THROW( Unimplemented_Feature );
}
FT_EXPORT_DEF( FT_Error )
FT_Library_SetLcdFilterWeights( FT_Library library,
unsigned char *weights )
@ -385,7 +411,7 @@
FT_UNUSED( library );
FT_UNUSED( weights );
return FT_Err_Ok;
return FT_THROW( Unimplemented_Feature );
}
@ -396,7 +422,7 @@
FT_UNUSED( library );
FT_UNUSED( filter );
return FT_Err_Ok;
return FT_THROW( Unimplemented_Feature );
}
#endif /* !FT_CONFIG_OPTION_SUBPIXEL_RENDERING */