[smooth] Implement minimal dynamic padding for LCD filtering.

Extra bitmap padding for LCD filtering depends on the filter.  The
default 5-tap filter needs 2 extra subpixels.  The light 3-tap filter
needs only 1 extra subpixel.  This space could be already available
due to rounding.  In order to optimize the padding, we now expand
CBox for the given filter weights before rounding.

This change breakes current Skia (and Firefox).

* include/freetype/internal/ftobjs.h (FT_LibraryRec)
[FT_CONFIG_OPTION_SUBPIXEL_RENDERING]: Remove `lcd_extra' field.

* src/base/ftlcdfil.c (FT_Library_SetLcdFilterWeights,
FT_Library_SetLcdFilter): Remove `lcd_extra' initializations.

* src/smooth/ftsmooth.c (ft_smooth_render_generic): Implement dymanic
LCD padding.

4 files changed, 44 insertions, 33 deletions

diff --git a/ChangeLog b/ChangeLog
index c78412264..5e41f88cc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,24 @@
+2017-05-20  Alexei Podtelezhnikov  <apodtele@gmail.com>
+
+	[smooth] Implement minimal dynamic padding for LCD filtering.
+
+	Extra bitmap padding for LCD filtering depends on the filter.  The
+	default 5-tap filter needs 2 extra subpixels.  The light 3-tap filter
+	needs only 1 extra subpixel.  This space could be already available
+	due to rounding.  In order to optimize the padding, we now expand
+	CBox for the given filter weights before rounding.
+
+	This change breakes current Skia (and Firefox).
+
+	* include/freetype/internal/ftobjs.h (FT_LibraryRec)
+	[FT_CONFIG_OPTION_SUBPIXEL_RENDERING]: Remove `lcd_extra' field.
+
+	* src/base/ftlcdfil.c (FT_Library_SetLcdFilterWeights,
+	FT_Library_SetLcdFilter): Remove `lcd_extra' initializations.
+
+	* src/smooth/ftsmooth.c (ft_smooth_render_generic): Implement dymanic
+	LCD padding.
+
 2017-05-15  Werner Lemberg  <wl@gnu.org>
 
 	[sfnt] Return proper scaling values for SBIX bitmaps.
diff --git a/include/freetype/internal/ftobjs.h b/include/freetype/internal/ftobjs.h
index 06b6597ea..73961b95f 100644
--- a/include/freetype/internal/ftobjs.h
+++ b/include/freetype/internal/ftobjs.h
@@ -864,9 +864,6 @@ FT_BEGIN_HEADER
   /*    lcd_filter       :: If subpixel rendering is activated, the        */
   /*                        selected LCD filter mode.                      */
   /*                                                                       */
-  /*    lcd_extra        :: If subpixel rendering is activated, the number */
-  /*                        of extra pixels needed for the LCD filter.     */
-  /*                                                                       */
   /*    lcd_weights      :: If subpixel rendering is activated, the LCD    */
   /*                        filter weights, if any.                        */
   /*                                                                       */
@@ -902,7 +899,6 @@ FT_BEGIN_HEADER
 
 #ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
     FT_LcdFilter             lcd_filter;
-    FT_Int                   lcd_extra;        /* number of extra pixels */
     FT_LcdFiveTapFilter      lcd_weights;      /* filter weights, if any */
     FT_Bitmap_LcdFilterFunc  lcd_filter_func;  /* filtering callback     */
 #endif
diff --git a/src/base/ftlcdfil.c b/src/base/ftlcdfil.c
index 611b39f57..65dbf342e 100644
--- a/src/base/ftlcdfil.c
+++ b/src/base/ftlcdfil.c
@@ -296,7 +296,6 @@
 
     ft_memcpy( library->lcd_weights, weights, FT_LCD_FILTER_FIVE_TAPS );
     library->lcd_filter_func = ft_lcd_filter_fir;
-    library->lcd_extra       = 2;
 
     return FT_Err_Ok;
   }
@@ -319,7 +318,6 @@
     {
     case FT_LCD_FILTER_NONE:
       library->lcd_filter_func = NULL;
-      library->lcd_extra       = 0;
       break;
 
     case FT_LCD_FILTER_DEFAULT:
@@ -327,7 +325,6 @@
                  default_weights,
                  FT_LCD_FILTER_FIVE_TAPS );
       library->lcd_filter_func = ft_lcd_filter_fir;
-      library->lcd_extra       = 2;
       break;
 
     case FT_LCD_FILTER_LIGHT:
@@ -335,7 +332,6 @@
                  light_weights,
                  FT_LCD_FILTER_FIVE_TAPS );
       library->lcd_filter_func = ft_lcd_filter_fir;
-      library->lcd_extra       = 2;
       break;
 
 #ifdef USE_LEGACY
@@ -343,7 +339,6 @@
     case FT_LCD_FILTER_LEGACY:
     case FT_LCD_FILTER_LEGACY1:
       library->lcd_filter_func = _ft_lcd_filter_legacy;
-      library->lcd_extra       = 0;
       break;
 
 #endif
diff --git a/src/smooth/ftsmooth.c b/src/smooth/ftsmooth.c
index cd7a87b0f..061d251b1 100644
--- a/src/smooth/ftsmooth.c
+++ b/src/smooth/ftsmooth.c
@@ -119,7 +119,6 @@
 
 #ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
 
-    FT_Int                   lcd_extra          = 0;
     FT_LcdFiveTapFilter      lcd_weights        = { 0 };
     FT_Bool                  have_custom_weight = FALSE;
     FT_Bitmap_LcdFilterFunc  lcd_filter_func    = NULL;
@@ -147,13 +146,12 @@
     {
       /*
        * A per-font filter is set.  It always uses the default 5-tap
-       * in-place FIR filter that needs 2 extra pixels.
+       * in-place FIR filter.
        */
       ft_memcpy( lcd_weights,
                  slot->face->internal->lcd_weights,
                  FT_LCD_FILTER_FIVE_TAPS );
       lcd_filter_func = ft_lcd_filter_fir;
-      lcd_extra       = 2;
     }
     else
     {
@@ -167,7 +165,6 @@
                  slot->library->lcd_weights,
                  FT_LCD_FILTER_FIVE_TAPS );
       lcd_filter_func = slot->library->lcd_filter_func;
-      lcd_extra       = slot->library->lcd_extra;
     }
 
 #endif /*FT_CONFIG_OPTION_SUBPIXEL_RENDERING */
@@ -196,6 +193,28 @@
     /* taking into account the origin shift     */
     FT_Outline_Get_CBox( outline, &cbox );
 
+#ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
+    /* add minimal padding for LCD filter depending on specific weights */
+    if ( lcd_filter_func)
+    {
+      if ( hmul )
+      {
+        cbox.xMax += lcd_weights[4] ? 43
+                                    : lcd_weights[3] ? 22 : 0;
+        cbox.xMin -= lcd_weights[0] ? 43
+                                    : lcd_weights[1] ? 22 : 0;
+      }
+
+      if ( vmul )
+      {
+        cbox.yMax += lcd_weights[0] ? 43
+                                    : lcd_weights[1] ? 22 : 0;
+        cbox.yMin -= lcd_weights[4] ? 43
+                                    : lcd_weights[3] ? 22 : 0;
+      }
+    }
+#endif
+
     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 );
@@ -225,26 +244,6 @@
     if ( vmul )
       height *= 3;
 
-#ifdef FT_CONFIG_OPTION_SUBPIXEL_RENDERING
-    if ( lcd_filter_func )
-    {
-      if ( hmul )
-      {
-        x_shift += 64 * ( lcd_extra >> 1 );
-        x_left  -= lcd_extra >> 1;
-        width   += 3 * lcd_extra;
-        pitch    = FT_PAD_CEIL( width, 4 );
-      }
-
-      if ( vmul )
-      {
-        y_shift += 64 * ( lcd_extra >> 1 );
-        y_top   += lcd_extra >> 1;
-        height  += 3 * lcd_extra;
-      }
-    }
-#endif
-
     /*
      * XXX: on 16bit system, we return an error for huge bitmap
      * to prevent an overflow.