[Git][freetype/freetype][raster_2023] 3 commits: [raster] Simplify dropo

Alexei Podtelezhnikov pushed to branch raster_2023 at FreeType / FreeType

Commits:

dc519d06

by Alexei Podtelezhnikov (Алексей Подтележников) at 2023-10-31T15:01:32+00:00

[raster] Simplify dropout detection.

* src/raster/ftrater.c (Draw_Sweep): Use a single dropout condition.

f2e76e83

by Alexei Podtelezhnikov (Алексей Подтележников) at 2023-11-03T03:09:54+00:00

[raster] Remove the jitter exception.

The jitter exception used to be applied when two neighboring pixels
were barely inside the outline. One the left one was turned on then,
which contradicts the OpenType specifications.  Intended to remove
glitches, it caused disappearing lines and was softened by adding an
exception to the exception (#54589).

* src/raster/ftraster.c (Vertical_Sweep_Span): Drop the jitter exception.

6d6607b8

by Alexei Podtelezhnikov (Алексей Подтележников) at 2023-11-03T03:09:54+00:00

[raster] Modify the split condition.

While curving close to a pixel center, vertical and horizontal pass
might split the curve differently and cause a rare dropout.  This
makes the split condition invariant of the sweep direction and more
robust.

* src/raster/ftraster.c (Bezier_Up): Modify the split condition.

1 changed file:

src/raster/ftraster.c

Changes:

src/raster/ftraster.c

@@ -448,7 +448,6 @@
      Int         precision_half;
      Int         precision_scale;
      Int         precision_step;
 -    Int         precision_jitter;
      PLong       buff;               /* The profiles buffer                 */
      PLong       sizeBuff;           /* Render pool size                    */
@@ -549,27 +548,17 @@
+      *
       *   256 / (1 << 12) = 0.0625 pixels.
+      *
 -     * `precision_jitter' is an epsilon threshold used in
 -     * `Vertical_Sweep_Span' to deal with small imperfections in the Bezier
 -     * decomposition (after all, we are working with approximations only);
 -     * it avoids switching on additional pixels which would cause artifacts
 -     * otherwise.
 -     *
 -     * The value of `precision_jitter' has been determined heuristically.
 -     *
       */
      if ( High )
+     {
        ras.precision_bits   = 12;
        ras.precision_step   = 256;
 -      ras.precision_jitter = 30;
+     }
      else
+     {
        ras.precision_bits   = 6;
        ras.precision_step   = 32;
 -      ras.precision_jitter = 2;
+     }
      ras.precision       = 1 << ras.precision_bits;
@@ -1135,7 +1124,8 @@
                        Long       miny,
                        Long       maxy )
+   {
 -    Long   y1, y2, e, e2, e0;
 +    Long  y1, y2, e, e2, e0, dy;
 +    Long  dx, x2;
      TPoint*  start_arc;
@@ -1200,19 +1190,25 @@
        ras.joint = FALSE;
        y2 = arc[0].y;
 +      x2 = arc[0].x;
        if ( y2 > e )
+       {
 -        y1 = arc[degree].y;
 -        if ( y2 - y1 >= ras.precision_step )
 +        dy = y2 - arc[degree].y;
 +        dx = x2 - arc[degree].x;
++
++
 +        /* split condition should be invariant of direction */
 +        if (  dy > ras.precision_step ||
 +              dx > ras.precision_step ||
 +             -dx > ras.precision_step )
+         {
            splitter( arc );
            arc += degree;
+         }
          else
+         {
 -          *top++ = arc[degree].x + FMulDiv( arc[0].x - arc[degree].x,
 -                                            e - y1, y2 - y1 );
 +          *top++ = x2 - FMulDiv( y2 - e, dx, dy );
            arc -= degree;
            e   += ras.precision;
+         }
@@ -1222,7 +1218,7 @@
          if ( y2 == e )
+         {
            ras.joint  = TRUE;
 -          *top++     = arc[0].x;
 +          *top++     = x2;
            e += ras.precision;
+         }
@@ -2139,9 +2135,7 @@
                                  PProfile    left,
                                  PProfile    right )
+   {
 -    Long  e1, e2;
+-
 -    Int  dropOutControl = left->flags & 7;
 +    Int  e1, e2;
      FT_UNUSED( y );
      FT_UNUSED( left );
@@ -2153,20 +2147,8 @@
                  ras.precision_bits, (double)x1 / (double)ras.precision,
                  ras.precision_bits, (double)x2 / (double)ras.precision ));
 -    /* Drop-out control */
+-
 -    e1 = CEILING( x1 );
 -    e2 = FLOOR( x2 );
+-
 -    /* take care of the special case where both the left */
 -    /* and right contour lie exactly on pixel centers    */
 -    if ( dropOutControl != 2                             &&
 -         x2 - x1 - ras.precision <= ras.precision_jitter &&
 -         e1 != x1 && e2 != x2                            )
 -      e2 = e1;
+-
 -    e1 = TRUNC( e1 );
 -    e2 = TRUNC( e2 );
 +    e1 = (Int)TRUNC( CEILING( x1 ) );
 +    e2 = (Int)TRUNC( FLOOR( x2 ) );
      if ( e2 >= 0 && e1 < ras.bWidth )
+     {
@@ -2180,10 +2162,10 @@
        if ( e2 >= ras.bWidth )
          e2 = ras.bWidth - 1;
 -      FT_TRACE7(( " -> x=[%ld;%ld]", e1, e2 ));
 +      FT_TRACE7(( " -> x=[%d;%d]", e1, e2 ));
 -      c1 = (Int)( e1 >> 3 );
 -      c2 = (Int)( e2 >> 3 );
 +      c1 = e1 >> 3;
 +      c2 = e2 >> 3;
        f1 =  0xFF >> ( e1 & 7 );
        f2 = ~0x7F >> ( e2 & 7 );
@@ -2609,8 +2591,6 @@
      PProfile      P, Q, P_Left, P_Right;
 -    Long          x1, x2, xs, e1, e2;
+-
      TProfileList  waiting    = ras.fProfile;
      TProfileList  draw_left  = NULL;
      TProfileList  draw_right = NULL;
@@ -2683,8 +2663,10 @@
          while ( P_Left && P_Right )
+         {
 -          x1 = P_Left ->X;
 -          x2 = P_Right->X;
 +          Long  x1 = P_Left ->X;
 +          Long  x2 = P_Right->X;
 +          Long  xs;
++
            if ( x1 > x2 )
+           {
@@ -2693,36 +2675,24 @@
              x2 = xs;
+           }
 -          e1 = FLOOR( x1 );
 -          e2 = CEILING( x2 );
+-
 -          if ( x2 - x1 <= ras.precision &&
 -               e1 != x1 && e2 != x2     )
 +          /* if bottom ceiling exceeds top floor, it is a drop-out */
 +          if ( CEILING( x1 ) > FLOOR( x2 ) )
+           {
 -            if ( e1 > e2 || e2 == e1 + ras.precision )
 -            {
 -              Int  dropOutControl = P_Left->flags & 7;
+-
 +            Int  dropOutControl = P_Left->flags & 7;
 -              if ( dropOutControl != 2 )
 -              {
 -                /* a drop-out was detected */
 -                P_Left ->X = x1;
 -                P_Right->X = x2;
+-
 -                /* mark profile for drop-out processing */
 -                P_Left->countL = 1;
 -                dropouts++;
 -              }
 +            if ( dropOutControl != 2 )
 +            {
 +              P_Left ->X = x1;
 +              P_Right->X = x2;
 -              goto Skip_To_Next;
 +              /* mark profile for drop-out processing */
 +              P_Left->countL = 1;
 +              dropouts++;
+             }
+           }
+-
 -          ras.Proc_Sweep_Span( RAS_VARS y, x1, x2, P_Left, P_Right );
+-
 -        Skip_To_Next:
 +          else
 +            ras.Proc_Sweep_Span( RAS_VARS y, x1, x2, P_Left, P_Right );
            P_Left  = P_Left->link;
            P_Right = P_Right->link;

From:	Alexei Podtelezhnikov (@apodtele)
Subject:	[Git][freetype/freetype][raster_2023] 3 commits: [raster] Simplify dropout detection.
Date:	Fri, 03 Nov 2023 03:10:00 +0000