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Rewrite tessellate_rectangle as tessellate_convex_quad to make it more useful

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Currently there aren't even any users of this code, (they had
stopped using it when they realized what they really wanted
was tessellate_convex_quad).
This commit is contained in:
Carl Worth 2006-11-10 12:53:33 -08:00
parent e324bbcbc6
commit fefa7d9b99
2 changed files with 112 additions and 17 deletions
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127
src/cairo-traps.c
View file

@ -367,26 +367,121 @@ _cairo_traps_tessellate_triangle (cairo_traps_t *traps, cairo_point_t t[3])
return traps->status;
}
/* Warning: This function reorders the elements of the array provided. */
cairo_status_t
_cairo_traps_tessellate_rectangle (cairo_traps_t *traps, cairo_point_t q[4])
_cairo_traps_tessellate_convex_quad (cairo_traps_t *traps, cairo_point_t q[4])
{
qsort (q, 4, sizeof (cairo_point_t), _compare_point_fixed_by_y);
int a, b, c, d;
int i;
if (q[1].x > q[2].x) {
_cairo_traps_add_trap_from_points (traps,
q[0].y, q[1].y, q[0], q[2], q[0], q[1]);
_cairo_traps_add_trap_from_points (traps,
q[1].y, q[2].y, q[0], q[2], q[1], q[3]);
_cairo_traps_add_trap_from_points (traps,
q[2].y, q[3].y, q[2], q[3], q[1], q[3]);
/* Choose a as a point with minimal y */
a = 0;
for (i = 1; i < 4; i++)
if (_compare_point_fixed_by_y (&q[i], &q[a]) < 0)
a = i;
/* b and c are adjacent to a, while c is opposite */
b = (a + 1) % 4;
c = (a + 2) % 4;
d = (a + 3) % 4;
/* Choose between b and d so that b.y is less than d.y */
if (_compare_point_fixed_by_y (&q[d], &q[b]) < 0) {
b = (a + 3) % 4;
d = (a + 1) % 4;
}
/* Without freedom left to choose anything else, we have four
* cases to tessellate which we can distinguish by comparing c.y
* to d.y and then by comparing b.x to d.x. And then for any of
* these cases there is a trivial way to emit three
* trapezoids. The 4 cases and their trapezoids are described and
* implemented below:
*/
if (q[c].y < q[d].y) {
if (q[b].x < q[d].x) {
/* c.y < d.y && b.x < d.x
*
* top bot left right
* a
* / | a.y b.y ab ad
* b |
* | | b.y c.y bc ad
* c |
* \ | c.y d.y cd ad
* d
*/
_cairo_traps_add_trap_from_points (traps,
q[a].y, q[b].y,
q[a], q[b], q[a], q[d]);
_cairo_traps_add_trap_from_points (traps,
q[b].y, q[c].y,
q[b], q[c], q[a], q[d]);
_cairo_traps_add_trap_from_points (traps,
q[c].y, q[d].y,
q[c], q[d], q[a], q[d]);
} else {
/* c.y < d.y && b.x >= d.x
*
* a
* | \ a.y b.y ad ab
* | b
* | | b.y c.y ad bc
* | c
* | / c.y d.y ad cd
* d
*/
_cairo_traps_add_trap_from_points (traps,
q[a].y, q[b].y,
q[a], q[d], q[a], q[b]);
_cairo_traps_add_trap_from_points (traps,
q[b].y, q[c].y,
q[a], q[d], q[b], q[c]);
_cairo_traps_add_trap_from_points (traps,
q[c].y, q[d].y,
q[a], q[d], q[c], q[d]);
}
} else {
_cairo_traps_add_trap_from_points (traps,
q[0].y, q[1].y, q[0], q[1], q[0], q[2]);
_cairo_traps_add_trap_from_points (traps,
q[1].y, q[2].y, q[1], q[3], q[0], q[2]);
_cairo_traps_add_trap_from_points (traps,
q[2].y, q[3].y, q[1], q[3], q[2], q[3]);
if (q[b].x < q[d].x) {
/* c.y >= d.y && b.x < d.x
*
* a
* / \ a.y b.y ab ad
* b \
* \ \ b.y d.y bc ad
* \ d
* \ / d.y c.y bc dc
* c
*/
_cairo_traps_add_trap_from_points (traps,
q[a].y, q[b].y,
q[a], q[b], q[a], q[d]);
_cairo_traps_add_trap_from_points (traps,
q[b].y, q[d].y,
q[b], q[c], q[a], q[d]);
_cairo_traps_add_trap_from_points (traps,
q[d].y, q[c].y,
q[b], q[c], q[d], q[c]);
} else {
/* c.y >= d.y && b.x >= d.x
*
* a
* / \ a.y b.y ad ab
* / b
* / / b.y d.y ad bc
* d /
* \ / d.y c.y dc bc
* c
*/
_cairo_traps_add_trap_from_points (traps,
q[a].y, q[b].y,
q[a], q[d], q[a], q[b]);
_cairo_traps_add_trap_from_points (traps,
q[b].y, q[d].y,
q[a], q[d], q[b], q[c]);
_cairo_traps_add_trap_from_points (traps,
q[d].y, q[c].y,
q[d], q[c], q[b], q[c]);
}
}
return traps->status;

2
src/cairoint.h
View file

@ -2223,7 +2223,7 @@ cairo_private cairo_status_t
_cairo_traps_tessellate_triangle (cairo_traps_t *traps, cairo_point_t t[3]);
cairo_private cairo_status_t
_cairo_traps_tessellate_rectangle (cairo_traps_t *traps, cairo_point_t q[4]);
_cairo_traps_tessellate_convex_quad (cairo_traps_t *traps, cairo_point_t q[4]);
cairo_private cairo_status_t
_cairo_traps_tessellate_polygon (cairo_traps_t *traps,