Commit 42206ad86aac3c3c344fcd9730d80165514584c9
2009-06-16T15:14:21
Improve scan conversion rules 4 and 6. Two new constraints are introduced to better identify a `stub' -- a concept which is only vaguely described in the OpenType specification. The old code was too rigorous and suppressed more pixel than it should. . The intersection of the two profiles with the scanline is less than a half pixel. Code related to this was already present in the sources but has been commented out. . The endpoint of the original contour forming a profile has a distance (`overshoot') less than half a pixel to the scanline. Note that the two additional conditions fix almost all differences to the Windows rasterizer, but some problematic cases remain. * src/raster/ftraster.c (Overshoot_Top, Overshoot_Bottom): New macros for the `flags' field in the `TProfile' structure. (IS_BOTTOM_OVERSHOOT, IS_TOP_OVERSHOOT): New macros. (New_Profile, End_Profile): Pass overshoot flag as an argument and set it accordingly. Update callers. (Vertical_Sweep_Drop, Horizontal_Sweep_Drop): Implement the two new constraints.
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diff --git a/ChangeLog b/ChangeLog
index 6edf105..22b2a34 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,31 @@
+2009-06-16 Werner Lemberg <wl@gnu.org>
+
+ Improve scan conversion rules 4 and 6.
+
+ Two new constraints are introduced to better identify a `stub' -- a
+ concept which is only vaguely described in the OpenType
+ specification. The old code was too rigorous and suppressed more
+ pixel than it should.
+
+ . The intersection of the two profiles with the scanline is less
+ than a half pixel. Code related to this was already present in
+ the sources but has been commented out.
+
+ . The endpoint of the original contour forming a profile has a
+ distance (`overshoot') less than half a pixel to the scanline.
+
+ Note that the two additional conditions fix almost all differences
+ to the Windows rasterizer, but some problematic cases remain.
+
+ * src/raster/ftraster.c (Overshoot_Top, Overshoot_Bottom): New
+ macros for the `flags' field in the `TProfile' structure.
+ (IS_BOTTOM_OVERSHOOT, IS_TOP_OVERSHOOT): New macros.
+ (New_Profile, End_Profile): Pass overshoot flag as an argument and
+ set it accordingly.
+ Update callers.
+ (Vertical_Sweep_Drop, Horizontal_Sweep_Drop): Implement the two new
+ constraints.
+
2009-06-11 Werner Lemberg <wl@gnu.org>
Increase precision for B/W rasterizer.
diff --git a/src/raster/ftraster.c b/src/raster/ftraster.c
index 5ade13b..c8c13f2 100644
--- a/src/raster/ftraster.c
+++ b/src/raster/ftraster.c
@@ -305,7 +305,10 @@
} TPoint;
-#define Flow_Up 0x1
+ /* values for the `flags' bit field */
+#define Flow_Up 0x1
+#define Overshoot_Top 0x2
+#define Overshoot_Bottom 0x4
/* States of each line, arc, and profile */
@@ -324,18 +327,19 @@
struct TProfile_
{
- FT_F26Dot6 X; /* current coordinate during sweep */
- PProfile link; /* link to next profile (various purposes) */
- PLong offset; /* start of profile's data in render pool */
- unsigned flags; /* Bit 0: profile orientation: up/down */
- long height; /* profile's height in scanlines */
- long start; /* profile's starting scanline */
-
- unsigned countL; /* number of lines to step before this */
- /* profile becomes drawable */
-
- PProfile next; /* next profile in same contour, used */
- /* during drop-out control */
+ FT_F26Dot6 X; /* current coordinate during sweep */
+ PProfile link; /* link to next profile (various purposes) */
+ PLong offset; /* start of profile's data in render pool */
+ unsigned flags; /* Bit 0: profile orientation (up/down) */
+ /* Bit 1, 2: profile overshoot (top/bottom) */
+ long height; /* profile's height in scanlines */
+ long start; /* profile's starting scanline */
+
+ unsigned countL; /* number of lines to step before this */
+ /* profile becomes drawable */
+
+ PProfile next; /* next profile in same contour, used */
+ /* during drop-out control */
};
typedef PProfile TProfileList;
@@ -410,6 +414,9 @@
#define FRAC( x ) ( (x) & ( ras.precision - 1 ) )
#define SCALED( x ) ( ( (x) << ras.scale_shift ) - ras.precision_half )
+#define IS_BOTTOM_OVERSHOOT( x ) ( CEILING( x ) - x >= ras.precision_half )
+#define IS_TOP_OVERSHOOT( x ) ( x - FLOOR( x ) >= ras.precision_half )
+
/* Note that I have moved the location of some fields in the */
/* structure to ensure that the most used variables are used */
/* at the top. Thus, their offset can be coded with less */
@@ -617,14 +624,18 @@
/* Create a new profile in the render pool. */
/* */
/* <Input> */
- /* aState :: The state/orientation of the new profile. */
+ /* aState :: The state/orientation of the new profile. */
+ /* */
+ /* overshoot :: Whether the profile's unrounded start position */
+ /* differs by at least a half pixel. */
/* */
/* <Return> */
/* SUCCESS on success. FAILURE in case of overflow or of incoherent */
/* profile. */
/* */
static Bool
- New_Profile( RAS_ARGS TStates aState )
+ New_Profile( RAS_ARGS TStates aState,
+ Bool overshoot )
{
if ( !ras.fProfile )
{
@@ -639,15 +650,26 @@
return FAILURE;
}
+ ras.cProfile->flags = 0;
+ ras.cProfile->start = 0;
+ ras.cProfile->height = 0;
+ ras.cProfile->offset = ras.top;
+ ras.cProfile->link = (PProfile)0;
+ ras.cProfile->next = (PProfile)0;
+
switch ( aState )
{
case Ascending_State:
ras.cProfile->flags |= Flow_Up;
+ if ( overshoot )
+ ras.cProfile->flags |= Overshoot_Bottom;
+
FT_TRACE6(( "New ascending profile = %lx\n", (long)ras.cProfile ));
break;
case Descending_State:
- ras.cProfile->flags &= ~Flow_Up;
+ if ( overshoot )
+ ras.cProfile->flags |= Overshoot_Top;
FT_TRACE6(( "New descending profile = %lx\n", (long)ras.cProfile ));
break;
@@ -657,12 +679,6 @@
return FAILURE;
}
- ras.cProfile->start = 0;
- ras.cProfile->height = 0;
- ras.cProfile->offset = ras.top;
- ras.cProfile->link = (PProfile)0;
- ras.cProfile->next = (PProfile)0;
-
if ( !ras.gProfile )
ras.gProfile = ras.cProfile;
@@ -682,11 +698,15 @@
/* <Description> */
/* Finalize the current profile. */
/* */
+ /* <Input> */
+ /* overshoot :: Whether the profile's unrounded end position differs */
+ /* by at least a half pixel. */
+ /* */
/* <Return> */
/* SUCCESS on success. FAILURE in case of overflow or incoherency. */
/* */
static Bool
- End_Profile( RAS_ARG )
+ End_Profile( RAS_ARGS Bool overshoot )
{
Long h;
PProfile oldProfile;
@@ -706,15 +726,24 @@
FT_TRACE6(( "Ending profile %lx, start = %ld, height = %ld\n",
(long)ras.cProfile, ras.cProfile->start, h ));
- oldProfile = ras.cProfile;
ras.cProfile->height = h;
- ras.cProfile = (PProfile)ras.top;
+ if ( overshoot )
+ {
+ if ( ras.cProfile->flags & Flow_Up )
+ ras.cProfile->flags |= Overshoot_Top;
+ else
+ ras.cProfile->flags |= Overshoot_Bottom;
+ }
- ras.top += AlignProfileSize;
+ oldProfile = ras.cProfile;
+ ras.cProfile = (PProfile)ras.top;
+
+ ras.top += AlignProfileSize;
ras.cProfile->height = 0;
ras.cProfile->offset = ras.top;
- oldProfile->next = ras.cProfile;
+
+ oldProfile->next = ras.cProfile;
ras.num_Profs++;
}
@@ -1328,13 +1357,15 @@
case Unknown_State:
if ( y > ras.lastY )
{
- if ( New_Profile( RAS_VARS Ascending_State ) )
+ if ( New_Profile( RAS_VARS Ascending_State,
+ IS_BOTTOM_OVERSHOOT( ras.lastY ) ) )
return FAILURE;
}
else
{
if ( y < ras.lastY )
- if ( New_Profile( RAS_VARS Descending_State ) )
+ if ( New_Profile( RAS_VARS Descending_State,
+ IS_TOP_OVERSHOOT( ras.lastY ) ) )
return FAILURE;
}
break;
@@ -1342,8 +1373,9 @@
case Ascending_State:
if ( y < ras.lastY )
{
- if ( End_Profile( RAS_VAR ) ||
- New_Profile( RAS_VARS Descending_State ) )
+ if ( End_Profile( RAS_VARS IS_TOP_OVERSHOOT( ras.lastY ) ) ||
+ New_Profile( RAS_VARS Descending_State,
+ IS_TOP_OVERSHOOT( ras.lastY ) ) )
return FAILURE;
}
break;
@@ -1351,8 +1383,9 @@
case Descending_State:
if ( y > ras.lastY )
{
- if ( End_Profile( RAS_VAR ) ||
- New_Profile( RAS_VARS Ascending_State ) )
+ if ( End_Profile( RAS_VARS IS_BOTTOM_OVERSHOOT( ras.lastY ) ) ||
+ New_Profile( RAS_VARS Ascending_State,
+ IS_BOTTOM_OVERSHOOT( ras.lastY ) ) )
return FAILURE;
}
break;
@@ -1367,13 +1400,13 @@
{
case Ascending_State:
if ( Line_Up( RAS_VARS ras.lastX, ras.lastY,
- x, y, ras.minY, ras.maxY ) )
+ x, y, ras.minY, ras.maxY ) )
return FAILURE;
break;
case Descending_State:
if ( Line_Down( RAS_VARS ras.lastX, ras.lastY,
- x, y, ras.minY, ras.maxY ) )
+ x, y, ras.minY, ras.maxY ) )
return FAILURE;
break;
@@ -1467,13 +1500,17 @@
state_bez = y1 < y3 ? Ascending_State : Descending_State;
if ( ras.state != state_bez )
{
+ Bool o = state_bez == Ascending_State ? IS_BOTTOM_OVERSHOOT( y1 )
+ : IS_TOP_OVERSHOOT( y1 );
+
+
/* finalize current profile if any */
if ( ras.state != Unknown_State &&
- End_Profile( RAS_VAR ) )
+ End_Profile( RAS_VARS o ) )
goto Fail;
/* create a new profile */
- if ( New_Profile( RAS_VARS state_bez ) )
+ if ( New_Profile( RAS_VARS state_bez, o ) )
goto Fail;
}
@@ -1599,11 +1636,16 @@
/* detect a change of direction */
if ( ras.state != state_bez )
{
+ Bool o = state_bez == Ascending_State ? IS_BOTTOM_OVERSHOOT( y1 )
+ : IS_TOP_OVERSHOOT( y1 );
+
+
+ /* finalize current profile if any */
if ( ras.state != Unknown_State &&
- End_Profile( RAS_VAR ) )
+ End_Profile( RAS_VARS o ) )
goto Fail;
- if ( New_Profile( RAS_VARS state_bez ) )
+ if ( New_Profile( RAS_VARS state_bez, o ) )
goto Fail;
}
@@ -1903,12 +1945,15 @@
for ( i = 0; i < ras.outline.n_contours; i++ )
{
+ Bool o;
+
+
ras.state = Unknown_State;
ras.gProfile = NULL;
if ( Decompose_Curve( RAS_VARS (unsigned short)start,
- ras.outline.contours[i],
- flipped ) )
+ ras.outline.contours[i],
+ flipped ) )
return FAILURE;
start = ras.outline.contours[i] + 1;
@@ -1917,15 +1962,19 @@
if ( FRAC( ras.lastY ) == 0 &&
ras.lastY >= ras.minY &&
ras.lastY <= ras.maxY )
- if ( ras.gProfile &&
- ( ras.gProfile->flags & Flow_Up ) ==
- ( ras.cProfile->flags & Flow_Up ) )
+ if ( ras.gProfile &&
+ ( ras.gProfile->flags & Flow_Up ) ==
+ ( ras.cProfile->flags & Flow_Up ) )
ras.top--;
/* Note that ras.gProfile can be nil if the contour was too small */
/* to be drawn. */
lastProfile = ras.cProfile;
- if ( End_Profile( RAS_VAR ) )
+ if ( ras.cProfile->flags & Flow_Up )
+ o = IS_TOP_OVERSHOOT( ras.lastY );
+ else
+ o = IS_BOTTOM_OVERSHOOT( ras.lastY );
+ if ( End_Profile( RAS_VARS o ) )
return FAILURE;
/* close the `next profile in contour' linked list */
@@ -2237,11 +2286,10 @@
/* Drop-out Control Rules #4 and #6 */
- /* The spec is not very clear regarding those rules. It */
- /* presents a method that is way too costly to implement */
- /* while the general idea seems to get rid of `stubs'. */
+ /* The specification neither provides an exact definition */
+ /* of a `stub' nor gives exact rules to exclude them. */
/* */
- /* Here, we only get rid of stubs recognized if: */
+ /* Here the constraints we use to recognize a stub. */
/* */
/* upper stub: */
/* */
@@ -2255,22 +2303,26 @@
/* - P_Left is the successor of P_Right in that contour */
/* - y is the bottom of P_Left */
/* */
+ /* We draw a stub if the following constraints are met. */
+ /* */
+ /* - for an upper or lower stub, there is top or bottom */
+ /* overshoot, respectively */
+ /* - the covered interval is greater or equal to a half */
+ /* pixel */
+
+ /* upper stub test */
+ if ( left->next == right &&
+ left->height <= 0 &&
+ !( left->flags & Overshoot_Top &&
+ x2 - x1 >= ras.precision_half ) )
+ return;
- /* FIXXXME: uncommenting this line solves the disappearing */
- /* bit problem in the `7' of verdana 10pts, but */
- /* makes a new one in the `C' of arial 14pts */
-#if 0
- if ( x2 - x1 < ras.precision_half )
-#endif
- {
- /* upper stub test */
- if ( left->next == right && left->height <= 0 )
- return;
-
- /* lower stub test */
- if ( right->next == left && left->start == y )
- return;
- }
+ /* lower stub test */
+ if ( right->next == left &&
+ left->start == y &&
+ !( left->flags & Overshoot_Bottom &&
+ x2 - x1 >= ras.precision_half ) )
+ return;
if ( ras.dropOutControl == 1 )
pxl = e2;
@@ -2432,11 +2484,17 @@
/* see Vertical_Sweep_Drop for details */
/* rightmost stub test */
- if ( left->next == right && left->height <= 0 )
+ if ( left->next == right &&
+ left->height <= 0 &&
+ !( left->flags & Overshoot_Top &&
+ x2 - x1 >= ras.precision_half ) )
return;
/* leftmost stub test */
- if ( right->next == left && left->start == y )
+ if ( right->next == left &&
+ left->start == y &&
+ !( left->flags & Overshoot_Bottom &&
+ x2 - x1 >= ras.precision_half ) )
return;
if ( ras.dropOutControl == 1 )
@@ -3064,7 +3122,7 @@
Set_High_Precision( RAS_VARS ras.outline.flags &
- FT_OUTLINE_HIGH_PRECISION );
+ FT_OUTLINE_HIGH_PRECISION );
ras.scale_shift = ras.precision_shift;
if ( ras.outline.flags & FT_OUTLINE_IGNORE_DROPOUTS )
@@ -3140,7 +3198,7 @@
Set_High_Precision( RAS_VARS ras.outline.flags &
- FT_OUTLINE_HIGH_PRECISION );
+ FT_OUTLINE_HIGH_PRECISION );
ras.scale_shift = ras.precision_shift + 1;
if ( ras.outline.flags & FT_OUTLINE_IGNORE_DROPOUTS )