mirror of
https://gitlab.freedesktop.org/freetype/freetype.git
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[base, smooth] Implement direct LCD filtering.
Applying an LCD filter to spans rather than the entire image improves the performance of ClearType-like rendering by about 40% at 32 ppem and much more at larger sizes. Small rounding differences are expected. * src/smooth/ftsmooth.c (ft_smooth_raster_lcd, ft_smooth_lcd_spans, ft_smooth_raster_lcdv, ft_smooth_lcdv_spans, TOrigin): Implement it. * include/freetype/internal/ftobjs.h (FT_LibraryRec): lcd_filter_func gone. * src/base/ftlcdfil.c (ft_lcd_filter_fir): Removed. (ft_lcd_padding): Use padding sufficient for any 5-tap filter. (FT_Library_SetLcdFilterWeights, FT_Library_SetLcdFilter): Updated. * docs/CHANGES: Updated.
This commit is contained in:
Alexei Podtelezhnikov
parent
e8f0969dcf
commit
7cc8f37b9a
4 changed files with 143 additions and 160 deletions
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@ -5,6 +5,11 @@ CHANGES BETWEEN 2.14.1 and 2.14.2 (2026-Mmm-DD)
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- Several changes related to LCD filtering are implemented to
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achieve better performance and encourage sound practices.
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. Instead of blanket LCD filtering over the entire bitmap, it is
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now applied only to non-zero spans using direct rendering. This
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speeds up the ClearType-like rendering by more than 40% at sizes
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above 32 ppem.
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. Setting the filter weights with FT_Face_Properties is no longer
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supported. The default and light filters are optimized to work
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with any face.
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@ -879,10 +879,6 @@ FT_BEGIN_HEADER
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* lcd_weights ::
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* The LCD filter weights for ClearType-style subpixel rendering.
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*
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* lcd_filter_func ::
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* The LCD filtering callback function for for ClearType-style subpixel
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* rendering.
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*
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* lcd_geometry ::
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* This array specifies LCD subpixel geometry and controls Harmony LCD
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* rendering technique, alternative to ClearType.
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@ -916,7 +912,6 @@ FT_BEGIN_HEADER
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#ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
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FT_LcdFiveTapFilter lcd_weights; /* filter weights, if any */
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FT_Bitmap_LcdFilterFunc lcd_filter_func; /* filtering callback */
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#else
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FT_Vector lcd_geometry[3]; /* RGB subpixel positions */
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#endif
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@ -25,142 +25,24 @@
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#ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
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#define FT_SHIFTCLAMP( x ) ( x >>= 8, (FT_Byte)( x > 255 ? 255 : x ) )
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/* add padding according to filter weights */
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/* add padding sufficient for a 5-tap filter, */
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/* which is 2/3 of a pixel */
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FT_BASE_DEF( void )
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ft_lcd_padding( FT_BBox* cbox,
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FT_GlyphSlot slot,
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FT_Render_Mode mode )
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{
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FT_Byte* lcd_weights;
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FT_Bitmap_LcdFilterFunc lcd_filter_func;
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FT_UNUSED( slot );
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lcd_weights = slot->library->lcd_weights;
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lcd_filter_func = slot->library->lcd_filter_func;
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if ( lcd_filter_func == ft_lcd_filter_fir )
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if ( mode == FT_RENDER_MODE_LCD )
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{
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if ( mode == FT_RENDER_MODE_LCD )
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{
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cbox->xMin -= lcd_weights[0] ? 43 :
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lcd_weights[1] ? 22 : 0;
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cbox->xMax += lcd_weights[4] ? 43 :
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lcd_weights[3] ? 22 : 0;
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}
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else if ( mode == FT_RENDER_MODE_LCD_V )
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{
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cbox->yMin -= lcd_weights[0] ? 43 :
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lcd_weights[1] ? 22 : 0;
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cbox->yMax += lcd_weights[4] ? 43 :
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lcd_weights[3] ? 22 : 0;
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}
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cbox->xMin -= 43;
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cbox->xMax += 43;
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}
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}
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/* FIR filter used by the default and light filters */
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FT_BASE_DEF( void )
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ft_lcd_filter_fir( FT_Bitmap* bitmap,
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FT_LcdFiveTapFilter weights )
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{
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FT_UInt width = (FT_UInt)bitmap->width;
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FT_UInt height = (FT_UInt)bitmap->rows;
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FT_Int pitch = bitmap->pitch;
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FT_Byte* origin = bitmap->buffer;
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FT_Byte mode = bitmap->pixel_mode;
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/* take care of bitmap flow */
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if ( pitch > 0 && height > 0 )
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origin += pitch * (FT_Int)( height - 1 );
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/* horizontal in-place FIR filter */
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if ( mode == FT_PIXEL_MODE_LCD && width >= 2 )
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else if ( mode == FT_RENDER_MODE_LCD_V )
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{
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FT_Byte* line = origin;
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/* `fir' must be at least 32 bit wide, since the sum of */
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/* the values in `weights' can exceed 0xFF */
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for ( ; height > 0; height--, line -= pitch )
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{
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FT_UInt fir[5];
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FT_UInt val, xx;
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val = line[0];
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fir[2] = weights[2] * val;
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fir[3] = weights[3] * val;
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fir[4] = weights[4] * val;
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val = line[1];
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fir[1] = fir[2] + weights[1] * val;
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fir[2] = fir[3] + weights[2] * val;
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fir[3] = fir[4] + weights[3] * val;
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fir[4] = weights[4] * val;
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for ( xx = 2; xx < width; xx++ )
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{
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val = line[xx];
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fir[0] = fir[1] + weights[0] * val;
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fir[1] = fir[2] + weights[1] * val;
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fir[2] = fir[3] + weights[2] * val;
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fir[3] = fir[4] + weights[3] * val;
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fir[4] = weights[4] * val;
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line[xx - 2] = FT_SHIFTCLAMP( fir[0] );
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}
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line[xx - 2] = FT_SHIFTCLAMP( fir[1] );
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line[xx - 1] = FT_SHIFTCLAMP( fir[2] );
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}
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}
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/* vertical in-place FIR filter */
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else if ( mode == FT_PIXEL_MODE_LCD_V && height >= 2 )
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{
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FT_Byte* column = origin;
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for ( ; width > 0; width--, column++ )
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{
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FT_Byte* col = column;
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FT_UInt fir[5];
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FT_UInt val, yy;
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val = col[0];
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fir[2] = weights[2] * val;
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fir[3] = weights[3] * val;
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fir[4] = weights[4] * val;
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col -= pitch;
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val = col[0];
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fir[1] = fir[2] + weights[1] * val;
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fir[2] = fir[3] + weights[2] * val;
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fir[3] = fir[4] + weights[3] * val;
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fir[4] = weights[4] * val;
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col -= pitch;
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for ( yy = 2; yy < height; yy++, col -= pitch )
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{
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val = col[0];
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fir[0] = fir[1] + weights[0] * val;
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fir[1] = fir[2] + weights[1] * val;
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fir[2] = fir[3] + weights[2] * val;
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fir[3] = fir[4] + weights[3] * val;
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fir[4] = weights[4] * val;
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col[pitch * 2] = FT_SHIFTCLAMP( fir[0] );
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}
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col[pitch * 2] = FT_SHIFTCLAMP( fir[1] );
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col[pitch] = FT_SHIFTCLAMP( fir[2] );
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}
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cbox->yMin -= 43;
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cbox->yMax += 43;
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}
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}
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@ -178,7 +60,6 @@
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return FT_THROW( Invalid_Argument );
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ft_memcpy( library->lcd_weights, weights, FT_LCD_FILTER_FIVE_TAPS );
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library->lcd_filter_func = ft_lcd_filter_fir;
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return FT_Err_Ok;
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}
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@ -202,21 +83,21 @@
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switch ( filter )
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{
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case FT_LCD_FILTER_NONE:
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library->lcd_filter_func = NULL;
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ft_memset( library->lcd_weights,
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0,
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FT_LCD_FILTER_FIVE_TAPS );
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break;
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case FT_LCD_FILTER_DEFAULT:
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ft_memcpy( library->lcd_weights,
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default_weights,
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FT_LCD_FILTER_FIVE_TAPS );
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library->lcd_filter_func = ft_lcd_filter_fir;
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break;
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case FT_LCD_FILTER_LIGHT:
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ft_memcpy( library->lcd_weights,
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light_weights,
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FT_LCD_FILTER_FIVE_TAPS );
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library->lcd_filter_func = ft_lcd_filter_fir;
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break;
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default:
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@ -80,6 +80,7 @@
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{
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unsigned char* origin; /* pixmap origin at the bottom-left */
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int pitch; /* pitch to go down one row */
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unsigned char wght[5]; /* filtering weights */
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} TOrigin;
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@ -274,6 +275,32 @@
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}
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/* This function applies a horizontal filter in direct rendering mode */
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static void
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ft_smooth_lcd_spans( int y,
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int count,
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const FT_Span* spans,
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void* target_ ) /* TOrigin* */
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{
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TOrigin* target = (TOrigin*)target_;
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unsigned char* dst_line = target->origin - y * target->pitch - 2;
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unsigned char* dst;
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unsigned short w;
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for ( ; count--; spans++ )
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for ( dst = dst_line + spans->x, w = spans->len; w--; dst++ )
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{
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dst[0] += ( spans->coverage * target->wght[0] + 85 ) >> 8;
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dst[1] += ( spans->coverage * target->wght[1] + 85 ) >> 8;
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dst[2] += ( spans->coverage * target->wght[2] + 85 ) >> 8;
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dst[3] += ( spans->coverage * target->wght[3] + 85 ) >> 8;
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dst[4] += ( spans->coverage * target->wght[4] + 85 ) >> 8;
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}
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}
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static FT_Error
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ft_smooth_raster_lcd( FT_Renderer render,
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FT_Outline* outline,
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@ -285,11 +312,47 @@
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FT_Vector* vec;
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FT_Raster_Params params;
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TOrigin target;
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params.target = bitmap;
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params.source = outline;
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params.flags = FT_RASTER_FLAG_AA;
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if ( render->root.library->lcd_weights[2] )
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{
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/* Reject outlines that are too wide for 16-bit FT_Span. */
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/* Other limits are applied upstream with the same error code. */
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if ( bitmap->width > 0x7FFF )
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return FT_THROW( Raster_Overflow );
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/* Set up direct rendering for instant filtering. */
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params.source = outline;
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params.flags = FT_RASTER_FLAG_AA | FT_RASTER_FLAG_DIRECT;
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params.gray_spans = ft_smooth_lcd_spans;
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params.user = ⌖
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params.clip_box.xMin = 0;
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params.clip_box.yMin = 0;
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params.clip_box.xMax = bitmap->width;
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params.clip_box.yMax = bitmap->rows;
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if ( bitmap->pitch < 0 )
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target.origin = bitmap->buffer;
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else
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target.origin = bitmap->buffer
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+ ( bitmap->rows - 1 ) * (unsigned int)bitmap->pitch;
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target.pitch = bitmap->pitch;
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target.wght[0] = render->root.library->lcd_weights[0];
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target.wght[1] = render->root.library->lcd_weights[1];
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target.wght[2] = render->root.library->lcd_weights[2];
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target.wght[3] = render->root.library->lcd_weights[3];
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target.wght[4] = render->root.library->lcd_weights[4];
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}
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else
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{
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params.target = bitmap;
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params.source = outline;
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params.flags = FT_RASTER_FLAG_AA;
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}
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/* implode outline */
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for ( vec = points; vec < points_end; vec++ )
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@ -306,6 +369,32 @@
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}
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/* This function applies a vertical filter in direct rendering mode */
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static void
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ft_smooth_lcdv_spans( int y,
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int count,
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const FT_Span* spans,
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void* target_ ) /* TOrigin* */
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{
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TOrigin* target = (TOrigin*)target_;
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int pitch = target->pitch;
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unsigned char* dst_line = target->origin - ( y + 2 ) * pitch;
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unsigned char* dst;
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unsigned short w;
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for ( ; count--; spans++ )
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for ( dst = dst_line + spans->x, w = spans->len; w--; dst++ )
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{
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dst[ 0] += ( spans->coverage * target->wght[0] + 85 ) >> 8;
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dst[ pitch] += ( spans->coverage * target->wght[1] + 85 ) >> 8;
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dst[2 * pitch] += ( spans->coverage * target->wght[2] + 85 ) >> 8;
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dst[3 * pitch] += ( spans->coverage * target->wght[3] + 85 ) >> 8;
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dst[4 * pitch] += ( spans->coverage * target->wght[4] + 85 ) >> 8;
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}
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}
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static FT_Error
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ft_smooth_raster_lcdv( FT_Renderer render,
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FT_Outline* outline,
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@ -317,11 +406,42 @@
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FT_Vector* vec;
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FT_Raster_Params params;
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TOrigin target;
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params.target = bitmap;
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params.source = outline;
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params.flags = FT_RASTER_FLAG_AA;
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if ( render->root.library->lcd_weights[2] )
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{
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/* Set up direct rendering for instant filtering. */
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params.source = outline;
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params.flags = FT_RASTER_FLAG_AA | FT_RASTER_FLAG_DIRECT;
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params.gray_spans = ft_smooth_lcdv_spans;
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params.user = ⌖
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params.clip_box.xMin = 0;
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params.clip_box.yMin = 0;
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params.clip_box.xMax = bitmap->width;
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params.clip_box.yMax = bitmap->rows;
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if ( bitmap->pitch < 0 )
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target.origin = bitmap->buffer;
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else
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target.origin = bitmap->buffer
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+ ( bitmap->rows - 1 ) * (unsigned int)bitmap->pitch;
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target.pitch = bitmap->pitch;
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target.wght[0] = render->root.library->lcd_weights[0];
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target.wght[1] = render->root.library->lcd_weights[1];
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target.wght[2] = render->root.library->lcd_weights[2];
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target.wght[3] = render->root.library->lcd_weights[3];
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target.wght[4] = render->root.library->lcd_weights[4];
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}
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else
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{
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params.target = bitmap;
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params.source = outline;
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params.flags = FT_RASTER_FLAG_AA;
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}
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/* implode outline */
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for ( vec = points; vec < points_end; vec++ )
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@ -521,24 +641,6 @@
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error = ft_smooth_raster_lcd ( render, outline, bitmap );
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else if ( mode == FT_RENDER_MODE_LCD_V )
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error = ft_smooth_raster_lcdv( render, outline, bitmap );
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#ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
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/* finally apply filtering */
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{
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FT_Byte* lcd_weights;
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FT_Bitmap_LcdFilterFunc lcd_filter_func;
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lcd_weights = slot->library->lcd_weights;
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lcd_filter_func = slot->library->lcd_filter_func;
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if ( lcd_filter_func )
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lcd_filter_func( bitmap, lcd_weights );
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}
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#endif /* FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
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}
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Exit:
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