Commit c02485cb725f94ea0487351596adc1e3ef8d1ae6
2011-01-13T21:55:08
[raster] Reduce jitter value. This catches a rendering problem with glyph `x' from Tahoma at 10ppem. It seems that the increase of the precision in the change from 2009-06-11 makes a larger jitter value unnecessary. * src/raster/ftraster.c (Set_High_Precision): Implement it.
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diff --git a/ChangeLog b/ChangeLog
index 5d25d78..06c4623 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
2011-01-13 Werner Lemberg <wl@gnu.org>
+ [raster] Reduce jitter value.
+
+ This catches a rendering problem with glyph `x' from Tahoma at
+ 10ppem. It seems that the increase of the precision in the change
+ from 2009-06-11 makes a larger jitter value unnecessary.
+
+ * src/raster/ftraster.c (Set_High_Precision): Implement it.
+
+2011-01-13 Werner Lemberg <wl@gnu.org>
+
[raster] Handle drop-outs at glyph borders according to Microsoft.
If a drop-out rule would switch on a pixel outside of the glyph's
diff --git a/src/raster/ftraster.c b/src/raster/ftraster.c
index a6d3179..92f65fc 100644
--- a/src/raster/ftraster.c
+++ b/src/raster/ftraster.c
@@ -4,7 +4,7 @@
/* */
/* The FreeType glyph rasterizer (body). */
/* */
-/* Copyright 1996-2001, 2002, 2003, 2005, 2007, 2008, 2009, 2010 by */
+/* Copyright 1996-2001, 2002, 2003, 2005, 2007, 2008, 2009, 2010, 2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@@ -651,11 +651,33 @@
static void
Set_High_Precision( RAS_ARGS Int High )
{
+ /*
+ * `precision_step' is used in `Bezier_Up' to decide when to split a
+ * given y-monotonous Bezier arc that crosses a scanline before
+ * approximating it as a straight segment. The default value of 32 (for
+ * low accuracy) corresponds to
+ *
+ * 32 / 64 == 0.5 pixels ,
+ *
+ * while for the high accuracy case we have
+ *
+ * 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 = 50;
+ ras.precision_jitter = 30;
}
else
{