ref: 410f3799b6a193e20b34c574e6f0f2be2428b1eb
parent: 5710ef989da2be3db21d875ac48eb980564c052b
author: Alexei Podtelezhnikov <[email protected]>
date: Wed Mar 8 19:08:38 EST 2017
[smooth] Harmony LCD rendering. This is a new technology for LCD-optimized rendering. It capitalizes on the fact that each color channel grid is shifted by a third of a pixel. Therefore it is logical to render 3 separate monochrome bitmaps shifting the outline by 1/3 pixel, and then combine them. Importantly, the resulting output does not require additional LCD filtering. * src/smooth/ftsmooth.c (ft_smooth_render_generic) [!FT_CONFIG_OPTION_SUBPIXEL_RENDERING]: Implement new LCD-optimized rendering. * include/freetype/ftlcdfil.h, include/freetype/freetype.h, include/freetype/config/ftoption.h, devel/ftoption.h: Updated documentation.
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,24 @@
2017-08-08 Alexei Podtelezhnikov <[email protected]>
+ [smooth] Harmony LCD rendering.
+
+ This is a new technology for LCD-optimized rendering. It capitalizes
+ on the fact that each color channel grid is shifted by a third of a
+ pixel. Therefore it is logical to render 3 separate monochrome
+ bitmaps shifting the outline by 1/3 pixel, and then combine them.
+ Importantly, the resulting output does not require additional LCD
+ filtering.
+
+ * src/smooth/ftsmooth.c (ft_smooth_render_generic)
+ [!FT_CONFIG_OPTION_SUBPIXEL_RENDERING]: Implement new LCD-optimized
+ rendering.
+
+ * include/freetype/ftlcdfil.h, include/freetype/freetype.h,
+ include/freetype/config/ftoption.h, devel/ftoption.h: Updated
+ documentation.
+
+2017-08-08 Alexei Podtelezhnikov <[email protected]>
+
* src/smooth/ftsmooth.c (ft_smooth_render_generic): Clean up.
2017-08-08 Alexei Podtelezhnikov <[email protected]>
--- a/devel/ftoption.h
+++ b/devel/ftoption.h
@@ -107,22 +107,19 @@
/*************************************************************************/
/* */
- /* Uncomment the line below if you want to activate sub-pixel rendering */
- /* (a.k.a. LCD rendering, or ClearType) in this build of the library. */
+ /* Uncomment the line below if you want to activate LCD rendering */
+ /* technology similar to ClearType in this build of the library. This */
+ /* technology triples the resolution in the direction color subpixels. */
+ /* To mitigate color fringes inherent to this technology, you also need */
+ /* to explicitly set up LCD filtering. */
/* */
/* Note that this feature is covered by several Microsoft patents */
/* and should not be activated in any default build of the library. */
+ /* When this macro is not defined, FreeType offers alternative LCD */
+ /* rendering technology that produces excellent output without LCD */
+ /* filtering. */
/* */
- /* This macro has no impact on the FreeType API, only on its */
- /* _implementation_. For example, using FT_RENDER_MODE_LCD when calling */
- /* FT_Render_Glyph still generates a bitmap that is 3 times wider than */
- /* the original size in case this macro isn't defined; however, each */
- /* triplet of subpixels has R=G=B. */
- /* */
- /* This is done to allow FreeType clients to run unmodified, forcing */
- /* them to display normal gray-level anti-aliased glyphs. */
- /* */
-#define FT_CONFIG_OPTION_SUBPIXEL_RENDERING
+/* #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
/*************************************************************************/
--- a/include/freetype/config/ftoption.h
+++ b/include/freetype/config/ftoption.h
@@ -107,20 +107,17 @@
/*************************************************************************/
/* */
- /* Uncomment the line below if you want to activate sub-pixel rendering */
- /* (a.k.a. LCD rendering, or ClearType) in this build of the library. */
+ /* Uncomment the line below if you want to activate LCD rendering */
+ /* technology similar to ClearType in this build of the library. This */
+ /* technology triples the resolution in the direction color subpixels. */
+ /* To mitigate color fringes inherent to this technology, you also need */
+ /* to explicitly set up LCD filtering. */
/* */
/* Note that this feature is covered by several Microsoft patents */
/* and should not be activated in any default build of the library. */
- /* */
- /* This macro has no impact on the FreeType API, only on its */
- /* _implementation_. For example, using FT_RENDER_MODE_LCD when calling */
- /* FT_Render_Glyph still generates a bitmap that is 3 times wider than */
- /* the original size in case this macro isn't defined; however, each */
- /* triplet of subpixels has R=G=B. */
- /* */
- /* This is done to allow FreeType clients to run unmodified, forcing */
- /* them to display normal gray-level anti-aliased glyphs. */
+ /* When this macro is not defined, FreeType offers alternative LCD */
+ /* rendering technology that produces excellent output without LCD */
+ /* filtering. */
/* */
/* #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -3131,11 +3131,13 @@
/* glyph outline in pixels and use the @FT_PIXEL_MODE_LCD_V mode. */
/* */
/* <Note> */
- /* The LCD-optimized glyph bitmaps produced by `FT_Render_Glyph' can */
- /* be filtered to reduce color-fringes by using */
- /* @FT_Library_SetLcdFilter (not active in the default builds). It */
- /* is up to the caller to either call `FT_Library_SetLcdFilter' (if */
- /* available) or do the filtering itself. */
+ /* Should you define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your */
+ /* `ftoption.h', which enables patented ClearType-style rendering, */
+ /* the LCD-optimized glyph bitmaps should be filtered to reduce color */
+ /* fringes inherent to this technology. You can either set up LCD */
+ /* filtering with @FT_Library_SetLcdFilter or @FT_Face_Properties, */
+ /* or do the filtering yourself. The default FreeType LCD rendering */
+ /* technology does not require filtering. */
/* */
/* The selected render mode only affects vector glyphs of a font. */
/* Embedded bitmaps often have a different pixel mode like */
--- a/include/freetype/ftlcdfil.h
+++ b/include/freetype/ftlcdfil.h
@@ -44,9 +44,16 @@
* Reduce color fringes of subpixel-rendered bitmaps.
*
* @description:
- * Subpixel rendering exploits the color-striped structure of LCD
- * pixels, increasing the available resolution in the direction of the
- * stripe (usually horizontal RGB) by a factor of~3. Since these
+ * Should you #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your
+ * `ftoption.h', which enables patented ClearType-style rendering,
+ * the LCD-optimized glyph bitmaps should be filtered to reduce color
+ * fringes inherent to this technology. The default FreeType LCD
+ * rendering uses different technology, and API described below,
+ * although available, does nothing.
+ *
+ * ClearType-style LCD rendering exploits the color-striped structure of
+ * LCD pixels, increasing the available resolution in the direction of
+ * the stripe (usually horizontal RGB) by a factor of~3. Since these
* subpixels are color pixels, using them unfiltered creates severe
* color fringes. Use the @FT_Library_SetLcdFilter API to specify a
* low-pass filter, which is then applied to subpixel-rendered bitmaps
@@ -53,12 +60,6 @@
* generated through @FT_Render_Glyph. The filter sacrifices some of
* the higher resolution to reduce color fringes, making the glyph image
* slightly blurrier. Positional improvements will remain.
- *
- * Note that no filter is active by default, and that this function is
- * *not* implemented in default builds of the library. You need to
- * #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your `ftoption.h' file
- * in order to activate it and explicitly call @FT_Library_SetLcdFilter
- * to enable it.
*
* A filter should have two properties:
*
--- a/src/smooth/ftsmooth.c
+++ b/src/smooth/ftsmooth.c
@@ -190,7 +190,23 @@
/* taking into account the origin shift */
FT_Outline_Get_CBox( outline, &cbox );
-#ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
+#ifndef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
+
+ /* add minimal padding for LCD rendering */
+ if ( hmul )
+ {+ cbox.xMax += 21;
+ cbox.xMin -= 21;
+ }
+
+ if ( vmul )
+ {+ cbox.yMax += 21;
+ cbox.yMin -= 21;
+ }
+
+#else /* FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
+
/* add minimal padding for LCD filter depending on specific weights */
if ( lcd_filter_func )
{@@ -210,8 +226,9 @@
: lcd_weights[1] ? 22 : 0;
}
}
-#endif
+#endif /* FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
+
cbox.xMin = FT_PIX_FLOOR( cbox.xMin + x_shift );
cbox.yMin = FT_PIX_FLOOR( cbox.yMin + y_shift );
cbox.xMax = FT_PIX_CEIL( cbox.xMax + x_shift );
@@ -339,57 +356,97 @@
#else /* !FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
- /* render outline into bitmap */
- error = render->raster_render( render->raster, ¶ms );
- if ( error )
- goto Exit;
-
- /* expand it horizontally */
- if ( hmul )
+ if ( hmul ) /* lcd */
{- FT_Byte* line = bitmap->buffer;
- FT_UInt hh;
+ FT_Byte* line;
+ FT_Byte* temp;
+ FT_Int i, j;
+ /* Render 3 separate monochrome bitmaps, shifting the outline */
+ /* by 1/3 pixel. */
+ width /= 3;
- for ( hh = height; hh > 0; hh--, line += pitch )
- {- FT_UInt xx;
- FT_Byte* end = line + width;
+ FT_Outline_Translate( outline, 21, 0 );
+ error = render->raster_render( render->raster, ¶ms );
+ if ( error )
+ goto Exit;
- for ( xx = width / 3; xx > 0; xx-- )
- {- FT_UInt pixel = line[xx-1];
+ FT_Outline_Translate( outline, -21, 0 );
+ bitmap->buffer += width;
+ error = render->raster_render( render->raster, ¶ms );
+ if ( error )
+ goto Exit;
- end[-3] = (FT_Byte)pixel;
- end[-2] = (FT_Byte)pixel;
- end[-1] = (FT_Byte)pixel;
- end -= 3;
+ FT_Outline_Translate( outline, -21, 0 );
+ bitmap->buffer += width;
+
+ error = render->raster_render( render->raster, ¶ms );
+ if ( error )
+ goto Exit;
+
+ FT_Outline_Translate( outline, 21, 0 );
+ bitmap->buffer -= 2 * width;
+
+ /* XXX: Rearrange the bytes according to FT_PIXEL_MODE_LCD. */
+ /* XXX: It is more efficient to render every third byte above. */
+
+ if ( FT_ALLOC( temp, (FT_ULong)pitch ) )
+ goto Exit;
+
+ for ( i = 0; i < height; i++ )
+ {+ line = bitmap->buffer + i * pitch;
+ for ( j = 0; j < width; j++ )
+ {+ temp[3 * j ] = line[j];
+ temp[3 * j + 1] = line[j + width];
+ temp[3 * j + 2] = line[j + width + width];
}
+ FT_MEM_COPY( line, temp, pitch );
}
- }
- /* expand it vertically */
- if ( vmul )
+ FT_FREE( temp );
+ }
+ else if ( vmul ) /* lcd_v */
{- FT_Byte* read = bitmap->buffer + ( height - height / 3 ) * pitch;
- FT_Byte* write = bitmap->buffer;
- FT_UInt hh;
+ /* Render 3 separate monochrome bitmaps, shifting the outline */
+ /* by 1/3 pixel. Triple the pitch to render on each third row. */
+ bitmap->pitch *= 3;
+ bitmap->rows /= 3;
+ FT_Outline_Translate( outline, 0, 21 );
+ bitmap->buffer += 2 * pitch;
- for ( hh = height / 3; hh > 0; hh-- )
- {- ft_memcpy( write, read, pitch );
- write += pitch;
+ error = render->raster_render( render->raster, ¶ms );
+ if ( error )
+ goto Exit;
- ft_memcpy( write, read, pitch );
- write += pitch;
+ FT_Outline_Translate( outline, 0, -21 );
+ bitmap->buffer -= pitch;
- ft_memcpy( write, read, pitch );
- write += pitch;
- read += pitch;
- }
+ error = render->raster_render( render->raster, ¶ms );
+ if ( error )
+ goto Exit;
+
+ FT_Outline_Translate( outline, 0, -21 );
+ bitmap->buffer -= pitch;
+
+ error = render->raster_render( render->raster, ¶ms );
+ if ( error )
+ goto Exit;
+
+ FT_Outline_Translate( outline, 0, 21 );
+
+ bitmap->pitch /= 3;
+ bitmap->rows *= 3;
+ }
+ else /* grayscale */
+ {+ error = render->raster_render( render->raster, ¶ms );
+ if ( error )
+ goto Exit;
}
#endif /* !FT_CONFIG_OPTION_SUBPIXEL_RENDERING */