stroke: Convert the outlines into contour and then into a polygon

In step 1 of speeding up stroking, we introduce contours as a means for
tracking the connected edges around the stroke. By keeping track of
these chains, we can analyse the edges as we proceed and eliminate
redundant vertices speeding up rasterisation.

Coincidentally fixes line-width-tolerance (looks like a combination of
using spline tangent vectors and tolerance).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 18 insertions, 9 deletions

diff --git a/src/cairo-spline.c b/src/cairo-spline.c
index 016eceed8..2467178fd 100644
--- a/src/cairo-spline.c
+++ b/src/cairo-spline.c
@@ -67,22 +67,27 @@ _cairo_spline_init (cairo_spline_t *spline,
     else if (b->x != d->x || b->y != d->y)
 	_cairo_slope_init (&spline->final_slope, &spline->knots.b, &spline->knots.d);
     else
-	_cairo_slope_init (&spline->final_slope, &spline->knots.a, &spline->knots.d);
+	return FALSE; /* just treat this as a straight-line from a -> d */
 
     return TRUE;
 }
 
 static cairo_status_t
-_cairo_spline_add_point (cairo_spline_t *spline, cairo_point_t *point)
+_cairo_spline_add_point (cairo_spline_t *spline,
+			 const cairo_point_t *point,
+			 const cairo_point_t *knot)
 {
     cairo_point_t *prev;
+    cairo_slope_t slope;
 
     prev = &spline->last_point;
     if (prev->x == point->x && prev->y == point->y)
 	return CAIRO_STATUS_SUCCESS;
 
+    _cairo_slope_init (&slope, point, knot);
+
     spline->last_point = *point;
-    return spline->add_point_func (spline->closure, point);
+    return spline->add_point_func (spline->closure, point, &slope);
 }
 
 static void
@@ -184,13 +189,15 @@ _cairo_spline_error_squared (const cairo_spline_knots_t *knots)
 }
 
 static cairo_status_t
-_cairo_spline_decompose_into (cairo_spline_knots_t *s1, double tolerance_squared, cairo_spline_t *result)
+_cairo_spline_decompose_into (cairo_spline_knots_t *s1,
+			      double tolerance_squared,
+			      cairo_spline_t *result)
 {
     cairo_spline_knots_t s2;
     cairo_status_t status;
 
     if (_cairo_spline_error_squared (s1) < tolerance_squared)
-	return _cairo_spline_add_point (result, &s1->a);
+	return _cairo_spline_add_point (result, &s1->a, &s1->b);
 
     _de_casteljau (s1, &s2);
 
@@ -206,6 +213,7 @@ _cairo_spline_decompose (cairo_spline_t *spline, double tolerance)
 {
     cairo_spline_knots_t s1;
     cairo_status_t status;
+    cairo_slope_t slope;
 
     s1 = spline->knots;
     spline->last_point = s1.a;
@@ -213,7 +221,8 @@ _cairo_spline_decompose (cairo_spline_t *spline, double tolerance)
     if (unlikely (status))
 	return status;
 
-    return _cairo_spline_add_point (spline, &spline->knots.d);
+    _cairo_slope_init (&slope, &spline->knots.c, &spline->knots.d);
+    return spline->add_point_func (spline->closure, &spline->knots.d, &slope);
 }
 
 /* Note: this function is only good for computing bounds in device space. */
@@ -325,7 +334,7 @@ _cairo_spline_bound (cairo_spline_add_point_func_t add_point_func,
     c = -y0 + y1;
     FIND_EXTREMES (a, b, c);
 
-    status = add_point_func (closure, p0);
+    status = add_point_func (closure, p0, NULL);
     if (unlikely (status))
 	return status;
 
@@ -359,10 +368,10 @@ _cairo_spline_bound (cairo_spline_add_point_func_t add_point_func,
 
 	p.x = _cairo_fixed_from_double (x);
 	p.y = _cairo_fixed_from_double (y);
-	status = add_point_func (closure, &p);
+	status = add_point_func (closure, &p, NULL);
 	if (unlikely (status))
 	    return status;
     }
 
-    return add_point_func (closure, p3);
+    return add_point_func (closure, p3, NULL);
 }