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Fix _cairo_traps_tessellate_convex_quad to handle a == b

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This case was found in an attempt to use the convex_quad function
for tessellating triangles as well. Fortunately the fix is very
easy.
This commit is contained in:
Carl Worth 2007-03-14 16:30:48 -07:00
parent 96d8f58daf
commit 53ae6ea957
1 changed files with 13 additions and 1 deletions
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14
src/cairo-traps.c
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@ -1,5 +1,6 @@
/*
* Copyright © 2002 Keith Packard
* Copyright © 2007 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it either under the terms of the GNU Lesser General Public
@ -408,7 +409,18 @@ _cairo_traps_tessellate_convex_quad (cairo_traps_t *traps, cairo_point_t q[4])
* This should hopefully be made clear in the lame ASCII art
* below. Since the same slope comparison is used in all cases, we
* compute it before testing for the Y-value sort. */
_cairo_slope_init (&ab, &q[a], &q[b]);
/* Note: If a == b then the ab slope doesn't give us any
* information. In that case, we can replace it with the ac (or
* equivalenly the bc) slope which gives us exactly the same
* information we need. At worst the names of the identifiers ab
* and b_left_of_d are inaccurate in this case, (would be ac, and
* c_left_of_d). */
if (q[a].x == q[b].x && q[a].y == q[b].y)
_cairo_slope_init (&ab, &q[a], &q[c]);
else
_cairo_slope_init (&ab, &q[a], &q[b]);
_cairo_slope_init (&ad, &q[a], &q[d]);
b_left_of_d = (_cairo_slope_compare (&ab, &ad) > 0);