Re: [ft-devel] Light Autofit + RGB Filtering

[Behdad Esfahbod]

Maybe you can attach screenshots?

On 05/31/11 19:21, James Cloos wrote:
> A few months back aging eyes and displays forced me to change my UI font
> preferences.  Up until then I primarily used fonts which had stem widths
> of one pixel.  In fontconfig pattern syntax, I used faces such as:
> 
>   DejaVu Sans Mono:pixelsize=15:minspace=true:autohint=false
>   DejaVu Serif:pixelsize=15:minspace=true:autohint=false
> 
> After considerable testing, I ended up with:
> 
>   DejaVu Sans Mono:pixelsize=20:minspace=true:autohint=true
>   DejaVu Serif:pixelsize=20:minspace=true:autohint=true
> 
> as my preferences.
> 
> I had already had fontconfig configured to suggest freetype’s legacy
> lcd filter for instructed sfnt/glyf faces and its default filter for
> all other faces.
> 
> The buggest annoyance I hit was the fact that the autofitter adjusts
> glyphs’ advance widths.  The resulted in DejaVu Sans Mono’s asterisk
> glyph being a (sub-?)pixel wider than its space glyph, causing text
> to reposition in my Gnus Summary buffers when I *-tagged messages.
> 
> Fontconfig and freetype make it easy to force lcd filtering and autofit,
> but I do not see any easy way to get lcd filtering with light autofit.
> 
> I first tested a ft patch which only avoided changes to advance width.
> That produced ugly output.
> 
> The below patch changes every test for (mode == FT_RENDER_MODE_LIGHT)
> to (true) and (mode != FT_RENDER_MODE_LIGHT) to (false).
> 
> To my eyes, on this display, the results look substantially better than
> the defaults for autofit+lcd.  The horizontal stems tend to get fit to a
> single pixel tall and the vertical stems tend to be one of 1+3+1, 1+3+2,
> 2+3+1 or 2+3+2 sub-pixels wide.  Which looks crisp; I cannot see any
> colour fringing at all.
> 
> IIRC, David at some point expressed a preference for the light autofit.
> 
> I’ve come to strongly agree.
> 
> I think we should look into making autofit fit in a single direction
> by default.
> 
> The patch is not meant for upstreaming, but rather to allow easy testing
> and to be mostly self-documenting:
> 
> 
> diff --git a/src/autofit/afcjk.c b/src/autofit/afcjk.c
> index d7670f4..ae2a18a 100644
> --- a/src/autofit/afcjk.c
> +++ b/src/autofit/afcjk.c
> @@ -1303,7 +1303,7 @@
>      /*
>       *  We adjust stems to full pixels only if we don't use the `light' mode.
>       */
> -    if ( mode != FT_RENDER_MODE_LIGHT )
> +    if ( 0 )
>        other_flags |= AF_LATIN_HINTS_STEM_ADJUST;
>  
>      if ( mode == FT_RENDER_MODE_MONO )
> diff --git a/src/autofit/aflatin.c b/src/autofit/aflatin.c
> index b939938..9b25781 100644
> --- a/src/autofit/aflatin.c
> +++ b/src/autofit/aflatin.c
> @@ -1495,7 +1495,7 @@
>      /*
>       *  We adjust stems to full pixels only if we don't use the `light' mode.
>       */
> -    if ( mode != FT_RENDER_MODE_LIGHT )
> +    if ( 0 )
>        other_flags |= AF_LATIN_HINTS_STEM_ADJUST;
>  
>      if ( mode == FT_RENDER_MODE_MONO )
> @@ -1505,7 +1505,7 @@
>       *  In `light' hinting mode we disable horizontal hinting completely.
>       *  We also do it if the face is italic.
>       */
> -    if ( mode == FT_RENDER_MODE_LIGHT                      ||
> +    if ( 1                      ||
>           ( face->style_flags & FT_STYLE_FLAG_ITALIC ) != 0 )
>        scaler_flags |= AF_SCALER_FLAG_NO_HORIZONTAL;
>  
> @@ -2235,7 +2235,7 @@
>  
>      /* analyze glyph outline */
>  #ifdef AF_CONFIG_OPTION_USE_WARPER
> -    if ( metrics->root.scaler.render_mode == FT_RENDER_MODE_LIGHT ||
> +    if ( 1 ||
>           AF_HINTS_DO_HORIZONTAL( hints )                          )
>  #else
>      if ( AF_HINTS_DO_HORIZONTAL( hints ) )
> @@ -2260,7 +2260,7 @@
>      {
>  #ifdef AF_CONFIG_OPTION_USE_WARPER
>        if ( dim == AF_DIMENSION_HORZ                                 &&
> -           metrics->root.scaler.render_mode == FT_RENDER_MODE_LIGHT )
> +           1 )
>        {
>          AF_WarperRec  warper;
>          FT_Fixed      scale;
> diff --git a/src/autofit/aflatin2.c b/src/autofit/aflatin2.c
> index d84e53a..efdd74f 100644
> --- a/src/autofit/aflatin2.c
> +++ b/src/autofit/aflatin2.c
> @@ -1512,7 +1512,7 @@
>      /*
>       *  We adjust stems to full pixels only if we don't use the `light' mode.
>       */
> -    if ( mode != FT_RENDER_MODE_LIGHT )
> +    if ( 0 )
>        other_flags |= AF_LATIN_HINTS_STEM_ADJUST;
>  
>      if ( mode == FT_RENDER_MODE_MONO )
> @@ -1522,7 +1522,7 @@
>       *  In `light' hinting mode we disable horizontal hinting completely.
>       *  We also do it if the face is italic.
>       */
> -    if ( mode == FT_RENDER_MODE_LIGHT                    ||
> +    if ( 1                    ||
>           (face->style_flags & FT_STYLE_FLAG_ITALIC) != 0 )
>        scaler_flags |= AF_SCALER_FLAG_NO_HORIZONTAL;
>  
> @@ -2286,7 +2286,7 @@
>  
>      /* analyze glyph outline */
>  #ifdef AF_CONFIG_OPTION_USE_WARPER
> -    if ( metrics->root.scaler.render_mode == FT_RENDER_MODE_LIGHT ||
> +    if ( 1 ||
>           AF_HINTS_DO_HORIZONTAL( hints ) )
>  #else
>      if ( AF_HINTS_DO_HORIZONTAL( hints ) )
> @@ -2311,7 +2311,7 @@
>      {
>  #ifdef AF_CONFIG_OPTION_USE_WARPER
>        if ( ( dim == AF_DIMENSION_HORZ &&
> -             metrics->root.scaler.render_mode == FT_RENDER_MODE_LIGHT ) )
> +             1 ) )
>        {
>          AF_WarperRec  warper;
>          FT_Fixed      scale;
> diff --git a/src/autofit/afloader.c b/src/autofit/afloader.c
> index 966a0df..00c4acc 100644
> --- a/src/autofit/afloader.c
> +++ b/src/autofit/afloader.c
> @@ -181,7 +181,7 @@
>  
>        /* we now need to adjust the metrics according to the change in */
>        /* width/positioning that occurred during the hinting process   */
> -      if ( scaler->render_mode != FT_RENDER_MODE_LIGHT )
> +      if ( 0 )
>        {
>          FT_Pos        old_rsb, old_lsb, new_lsb;
>          FT_Pos        pp1x_uh, pp2x_uh;
> diff --git a/src/pshinter/pshalgo.c b/src/pshinter/pshalgo.c
> index d798978..847763b 100644
> --- a/src/pshinter/pshalgo.c
> +++ b/src/pshinter/pshalgo.c
> @@ -658,7 +658,7 @@
>    }
>  
>  
> -#if 0  /* not used for now, experimental */
> +#if 1  /* not used for now, experimental */
>  
>   /*
>    *  A variant to perform "light" hinting (i.e. FT_RENDER_MODE_LIGHT)
> @@ -2260,7 +2260,7 @@
>        glyph->do_vert_snapping = FT_BOOL( hint_mode == FT_RENDER_MODE_MONO  ||
>                                           hint_mode == FT_RENDER_MODE_LCD_V );
>  
> -      glyph->do_stem_adjust   = FT_BOOL( hint_mode != FT_RENDER_MODE_LIGHT );
> +      glyph->do_stem_adjust   = FT_BOOL( 0 );
>  
>        for ( dimension = 0; dimension < 2; dimension++ )
>        {
> 
> 
> -JimC