diff options
author | Carl Worth <cworth@cworth.org> | 2008-02-14 11:50:26 -0800 |
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committer | Carl Worth <cworth@cworth.org> | 2008-02-20 04:04:03 -0800 |
commit | 2d22d698d32575fd883d2be072c041709254c86d (patch) | |
tree | 8116d1265f71a15b0e6403623fde6a9c817f6176 /src/cairo-slope.c | |
parent | 9292c0a1b509ecea8415cdbc21415d9ce7615e04 (diff) | |
download | cairo-2d22d698d32575fd883d2be072c041709254c86d.tar.gz |
Make _cairo_slope_compare return a non-zero result for slopes that differ by pi
This was an initial attempt to fix the infinite loop bug
described here:
Infinite loop when scaling very small values using 24.8
http://bugs.freedesktop.org/show_bug.cgi?id=14280
This doesn't actually fix that bug, but having a more robust
comparison function can only be a good thing.
Diffstat (limited to 'src/cairo-slope.c')
-rw-r--r-- | src/cairo-slope.c | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/src/cairo-slope.c b/src/cairo-slope.c index e8421fc35..af97a6399 100644 --- a/src/cairo-slope.c +++ b/src/cairo-slope.c @@ -47,8 +47,15 @@ _cairo_slope_init (cairo_slope_t *slope, cairo_point_t *a, cairo_point_t *b) positive X axis and increase in the direction of the positive Y axis. - WARNING: This function only gives correct results if the angular - difference between a and b is less than PI. + This function always compares the slope vectors based on the + smaller angular difference between them, (that is based on an + angular difference that is strictly less than pi). To break ties + when comparing slope vectors with an angular difference of exactly + pi, the vector with a positive dx (or positive dy if dx's are zero) + is considered to be more positive than the other. + + Also, all slope vectors with both dx==0 and dy==0 are considered + equal and more positive than any non-zero vector. < 0 => a less positive than b == 0 => a equal to b @@ -78,6 +85,25 @@ _cairo_slope_compare (cairo_slope_t *a, cairo_slope_t *b) if (b->dx == 0 && b->dy ==0) return -1; + /* Finally, we're looking at two vectors that are either equal or + * that differ by exactly pi. We can identify the "differ by pi" + * case by looking for a change in sign in either dx or dy between + * a and b. + * + * And in these cases, we eliminate the ambiguity by reducing the angle + * of b by an infinitesimally small amount, (that is, 'a' will + * always be considered less than 'b'). + */ + if (((a->dx > 0) != (b->dx > 0)) || + ((a->dy > 0) != (b->dy > 0))) + { + if (a->dx > 0 || (a->dx == 0 && a->dy > 0)) + return +1; + else + return -1; + } + + /* Finally, for identical slopes, we obviously return 0. */ return 0; } |