Improve stroking of densely dashed styles

Add some auxiliary functions to cairo-stroke-style to compute
properties of the dashed patterns (period, "on" coverage) and to
generate approximations when the dash pattern is sub-tolerance.
These functions are used in cairo-path-stroke to simplify dash
patterns stroked by cairo.
Fixes dash-infinite-loop
See http://bugs.freedesktop.org/show_bug.cgi?id=24702

1 files changed, 18 insertions, 6 deletions

diff --git a/src/cairo-path-stroke.c b/src/cairo-path-stroke.c
index 5c4f4fc7b..272045a87 100644
--- a/src/cairo-path-stroke.c
+++ b/src/cairo-path-stroke.c
@@ -51,6 +51,7 @@ typedef struct _cairo_stroker_dash {
 
     double dash_offset;
     const double *dashes;
+    double approximate_dashes[2];
     unsigned int num_dashes;
 } cairo_stroker_dash_t;
 
@@ -137,15 +138,25 @@ _cairo_stroker_dash_step (cairo_stroker_dash_t *dash, double step)
 
 static void
 _cairo_stroker_dash_init (cairo_stroker_dash_t *dash,
-			  const cairo_stroke_style_t *style)
+			  const cairo_stroke_style_t *style,
+			  const cairo_matrix_t *ctm,
+			  double tolerance)
 {
     dash->dashed = style->dash != NULL;
     if (! dash->dashed)
 	return;
 
-    dash->dashes = style->dash;
-    dash->num_dashes = style->num_dashes;
-    dash->dash_offset = style->dash_offset;
+    if (_cairo_stroke_style_dash_can_approximate (style, ctm, tolerance)) {
+	_cairo_stroke_style_dash_approximate (style, ctm, tolerance,
+					      &dash->dash_offset,
+					      dash->approximate_dashes,
+					      &dash->num_dashes);
+	dash->dashes = dash->approximate_dashes;
+    } else {
+	dash->dashes = style->dash;
+	dash->num_dashes = style->num_dashes;
+	dash->dash_offset = style->dash_offset;
+    }
 
     _cairo_stroker_dash_start (dash);
 }
@@ -179,7 +190,7 @@ _cairo_stroker_init (cairo_stroker_t		*stroker,
     stroker->has_first_face = FALSE;
     stroker->has_initial_sub_path = FALSE;
 
-    _cairo_stroker_dash_init (&stroker->dash, stroke_style);
+    _cairo_stroker_dash_init (&stroker->dash, stroke_style, ctm, tolerance);
 
     stroker->add_external_edge = NULL;
 
@@ -1490,7 +1501,8 @@ _cairo_rectilinear_stroker_init (cairo_rectilinear_stroker_t	*stroker,
     stroker->segments_size = ARRAY_LENGTH (stroker->segments_embedded);
     stroker->num_segments = 0;
 
-    _cairo_stroker_dash_init (&stroker->dash, stroke_style);
+    /* Assume 2*EPSILON tolerance */
+    _cairo_stroker_dash_init (&stroker->dash, stroke_style, ctm, _cairo_fixed_to_double (2 * CAIRO_FIXED_EPSILON));
 
     stroker->has_bounds = FALSE;
 }