[cairo] [PATCH 2/5] Move calculation of slope outside of _cairo_stroker_add_sub_edge.

[Jeff Muizelaar]

This makes the slope calculation more accurate for dashed lines by computing it
once for the entire line instead for each individual dash segment. It also
adjusts stroker_line_to() to match the new convention for
stroker_add_sub_edge().

---

diff --git a/src/cairo-path-stroke.c b/src/cairo-path-stroke.c
index 36cfcc6..633b048 100644
--- a/src/cairo-path-stroke.c
+++ b/src/cairo-path-stroke.c
@@ -548,11 +548,11 @@ _compute_face (cairo_point_t *point, cai
 
 static cairo_status_t
 _cairo_stroker_add_sub_edge (cairo_stroker_t *stroker, cairo_point_t *p1, cairo_point_t *p2,
-			     cairo_stroke_face_t *start, cairo_stroke_face_t *end)
+			     cairo_slope_t *slope, cairo_stroke_face_t *start,
+			     cairo_stroke_face_t *end)
 {
     cairo_status_t status;
     cairo_polygon_t polygon;
-    cairo_slope_t slope;
 
     if (p1->x == p2->x && p1->y == p2->y) {
 	/* XXX: Need to rethink how this case should be handled, (both
@@ -561,13 +561,12 @@ _cairo_stroker_add_sub_edge (cairo_strok
 	return CAIRO_STATUS_SUCCESS;
     }
 
-    _cairo_slope_init (&slope, p1, p2);
-    _compute_face (p1, &slope, stroker, start);
+    _compute_face (p1, slope, stroker, start);
 
     /* XXX: This could be optimized slightly by not calling
        _compute_face again but rather  translating the relevant
        fields from start. */
-    _compute_face (p2, &slope, stroker, end);
+    _compute_face (p2, slope, stroker, end);
 
     /* XXX: I should really check the return value of the
        move_to/line_to functions here to catch out of memory
@@ -623,6 +622,7 @@ _cairo_stroker_line_to (void *closure, c
     cairo_stroke_face_t start, end;
     cairo_point_t *p1 = &stroker->current_point;
     cairo_point_t *p2 = point;
+    cairo_slope_t slope;
 
     if (!stroker->has_current_point)
 	return _cairo_stroker_move_to (stroker, point);
@@ -634,8 +634,10 @@ _cairo_stroker_line_to (void *closure, c
            as possible. */
 	return CAIRO_STATUS_SUCCESS;
     }
+
+    _cairo_slope_init (&slope, p1, p2);
     
-    status = _cairo_stroker_add_sub_edge (stroker, p1, p2, &start, &end);
+    status = _cairo_stroker_add_sub_edge (stroker, p1, p2, &slope, &start, &end);
     if (status)
 	return status;
 
@@ -673,6 +675,7 @@ _cairo_stroker_line_to_dashed (void *clo
     cairo_stroke_face_t sub_start, sub_end;
     cairo_point_t *p1 = &stroker->current_point;
     cairo_point_t *p2 = point;
+    cairo_slope_t slope;
 
     if (!stroker->has_current_point)
 	return _cairo_stroker_move_to (stroker, point);
@@ -684,6 +687,8 @@ _cairo_stroker_line_to_dashed (void *clo
            as possible. */
 	return CAIRO_STATUS_SUCCESS;
     }
+
+    _cairo_slope_init (&slope, p1, p2);
 
     dx = _cairo_fixed_to_double (p2->x - p1->x);
     dy = _cairo_fixed_to_double (p2->y - p1->y);
@@ -709,7 +714,7 @@ _cairo_stroker_line_to_dashed (void *clo
 	 * XXX simplify this case analysis
 	 */
 	if (stroker->dash_on) {
-	    status = _cairo_stroker_add_sub_edge (stroker, &fd1, &fd2, &sub_start, &sub_end);
+	    status = _cairo_stroker_add_sub_edge (stroker, &fd1, &fd2, &slope, &sub_start, &sub_end);
 	    if (status)
 		return status;
 	    if (!first) {