[cairo-bugs] [Bug 7245] cairo_stroke_extents() gives wrong result for arcs in some cases

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=7245





------- Comment #4 from chris at chris-wilson.co.uk  2007-10-27 09:38 PST -------
I've worked around this problem by relaxing the check that the in and out faces
are exactly coincident, and instead just checking that if the two faces are
within stoker->tolerance of each other, then we need not do any work to join
the two faces and return SUCCESS.

@@ -205,17 +210,28 @@ _cairo_stroker_face_clockwise (cairo_stroke_face_t *in,
ca
     return _cairo_slope_clockwise (&in_slope, &out_slope);
 }

+static double
+_PointDistanceSquaredToPoint (const cairo_point_t *a, const cairo_point_t *b)
+{
+    double dx = _cairo_fixed_to_double (b->x - a->x);
+    double dy = _cairo_fixed_to_double (b->y - a->y);
+
+    return dx*dx + dy*dy;
+}
 static cairo_status_t
 _cairo_stroker_join (cairo_stroker_t *stroker, cairo_stroke_face_t *in,
cairo_s
 {
     int                        clockwise = _cairo_stroker_face_clockwise (out, 
     cairo_point_t      *inpt, *outpt;
     cairo_status_t status;
+    double tolerance_sqr = stroker->tolerance * stroker->tolerance;

-    if (in->cw.x == out->cw.x
+    if ((in->cw.x == out->cw.x
        && in->cw.y == out->cw.y
        && in->ccw.x == out->ccw.x
        && in->ccw.y == out->ccw.y)
+       || (_PointDistanceSquaredToPoint (&in->cw, &out->cw) < tolerance_sqr &&
+           _PointDistanceSquaredToPoint (&in->ccw, &out->ccw) <
tolerance_sqr))
     {
        return CAIRO_STATUS_SUCCESS;
     }

I'm a little hesitant to apply this as I'm uncertain as to whether this is just
papering over a deeper bug.


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