diff options
| -rw-r--r-- | src/cairo-path-fixed.c | 39 |
1 files changed, 27 insertions, 12 deletions
diff --git a/src/cairo-path-fixed.c b/src/cairo-path-fixed.c index 10a65159..14913fd0 100644 --- a/src/cairo-path-fixed.c +++ b/src/cairo-path-fixed.c @@ -1300,7 +1300,7 @@ _cairo_path_fixed_is_box (const cairo_path_fixed_t *path, } /* Determine whether two lines A->B and C->D intersect based on the - * algorithm described here: http://paulbourke.net/geometry/lineline2d/ */ + * algorithm described here: http://paulbourke.net/geometry/pointlineplane/ */ static inline cairo_bool_t _lines_intersect_or_are_coincident (cairo_point_t a, cairo_point_t b, @@ -1308,6 +1308,7 @@ _lines_intersect_or_are_coincident (cairo_point_t a, cairo_point_t d) { cairo_int64_t numerator_a, numerator_b, denominator; + cairo_bool_t denominator_negative; denominator = _cairo_int64_sub (_cairo_int32x32_64_mul (d.y - c.y, b.x - a.x), _cairo_int32x32_64_mul (d.x - c.x, b.y - a.y)); @@ -1327,20 +1328,34 @@ _lines_intersect_or_are_coincident (cairo_point_t a, return FALSE; } - /* If either division would produce a number between 0 and 1, i.e. - * the numerator is smaller than the denominator and their signs are - * the same, then the lines intersect. */ - if (_cairo_int64_lt (numerator_a, denominator) && - ! (_cairo_int64_negative (numerator_a) ^ _cairo_int64_negative(denominator))) { - return TRUE; - } + /* The lines intersect if both quotients are between 0 and 1 (exclusive). */ - if (_cairo_int64_lt (numerator_b, denominator) && - ! (_cairo_int64_negative (numerator_b) ^ _cairo_int64_negative(denominator))) { - return TRUE; + /* We first test whether either quotient is a negative number. */ + denominator_negative = _cairo_int64_negative (denominator); + if (_cairo_int64_negative (numerator_a) ^ denominator_negative) + return FALSE; + if (_cairo_int64_negative (numerator_b) ^ denominator_negative) + return FALSE; + + /* A zero quotient indicates an "intersection" at an endpoint, which + * we aren't considering a true intersection. */ + if (_cairo_int64_is_zero (numerator_a) || _cairo_int64_is_zero (numerator_b)) + return FALSE; + + /* If the absolute value of the numerator is larger than or equal to the + * denominator the result of the division would be greater than or equal + * to one. */ + if (! denominator_negative) { + if (! _cairo_int64_lt (numerator_a, denominator) || + ! _cairo_int64_lt (numerator_b, denominator)) + return FALSE; + } else { + if (! _cairo_int64_lt (denominator, numerator_a) || + ! _cairo_int64_lt (denominator, numerator_b)) + return FALSE; } - return FALSE; + return TRUE; } cairo_bool_t |