Fix assert caused by floating point error in tessellating path renderer.

Fix assert caused by floating point error in tessellating path renderer.

In rare cases, floating point error causes the tesselator to add the
same Vertex to more than one Poly on the same side. This was not a big
problem when we were allocating new vertices when constructing Polys,
but after https://codereview.chromium.org/2029243002 it causes more serious
issues, since each Edge can only belong to two Polys, and violating this
condition messes up the linked list of Edges used for left & right Polys
and the associated estimated vertex count.

The fix is to simply let the first Poly win, and skip that vertex for
subsequent Polys. Since this only occurs in cases where vertices are very
close to each other, it should have little visual effect.

This is also exercised by Nebraska-StateSeal.svg.

BUG=skia:5636
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259493002

Committed: https://skia.googlesource.com/skia/+/70f5251cc59191040a14cd0f1567aa2129e1f7c6

[Stephen White, 2016-08-17 18:37:45]

Description was changed from

==========
Fix assert caused by floating point error in tessellating path renderer.

In rare cases, floating point error causes the tesselator to add the
same Vertex to more than one Poly on the same side. This was not a big
problem when we were allocating new vertices when constructing Polys,
but after https://codereview.chromium.org/2029243002 it causes more serious
issues, since each Edge can only belong to two Polys, and violating this
condition messes up the linked list of Edges used for left & right Polys
and the associated estimated vertex count.

The fix is to simply let the first Poly win, and skip that vertex for
subsequent Polys. Since this only occurs in cases where vertices are very
close to each other, it should have little visual effect.

This is also exercised by Nebraska-StateSeal.svg.

BUG=skia:5636
==========

to

==========
Fix assert caused by floating point error in tessellating path renderer.

In rare cases, floating point error causes the tesselator to add the
same Vertex to more than one Poly on the same side. This was not a big
problem when we were allocating new vertices when constructing Polys,
but after https://codereview.chromium.org/2029243002 it causes more serious
issues, since each Edge can only belong to two Polys, and violating this
condition messes up the linked list of Edges used for left & right Polys
and the associated estimated vertex count.

The fix is to simply let the first Poly win, and skip that vertex for
subsequent Polys. Since this only occurs in cases where vertices are very
close to each other, it should have little visual effect.

This is also exercised by Nebraska-StateSeal.svg.

BUG=skia:5636
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259493002
==========

[Stephen White, 2016-08-17 18:38:27]

The CQ bit was checked by senorblanco@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-08-17 18:38:35]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Stephen White, 2016-08-17 18:50:01]

Description was changed from

==========
Fix assert caused by floating point error in tessellating path renderer.

In rare cases, floating point error causes the tesselator to add the
same Vertex to more than one Poly on the same side. This was not a big
problem when we were allocating new vertices when constructing Polys,
but after https://codereview.chromium.org/2029243002 it causes more serious
issues, since each Edge can only belong to two Polys, and violating this
condition messes up the linked list of Edges used for left & right Polys
and the associated estimated vertex count.

The fix is to simply let the first Poly win, and skip that vertex for
subsequent Polys. Since this only occurs in cases where vertices are very
close to each other, it should have little visual effect.

This is also exercised by Nebraska-StateSeal.svg.

BUG=skia:5636
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259493002
==========

to

==========
Fix assert caused by floating point error in tessellating path renderer.

In rare cases, floating point error causes the tesselator to add the
same Vertex to more than one Poly on the same side. This was not a big
problem when we were allocating new vertices when constructing Polys,
but after https://codereview.chromium.org/2029243002 it causes more serious
issues, since each Edge can only belong to two Polys, and violating this
condition messes up the linked list of Edges used for left & right Polys
and the associated estimated vertex count.

The fix is to simply let the first Poly win, and skip that vertex for
subsequent Polys. Since this only occurs in cases where vertices are very
close to each other, it should have little visual effect.

This is also exercised by Nebraska-StateSeal.svg.

BUG=skia:5636
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259493002
==========

[Stephen White, 2016-08-17 18:50:01]

senorblanco@chromium.org changed reviewers:
+ robertphillips@google.com

[Stephen White, 2016-08-17 18:50:10]

robertphillips@: PTAL. Thanks!

[commit-bot: I haz the power, 2016-08-17 19:43:12]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-08-17 19:43:13]

Dry run: This issue passed the CQ dry run.

[robertphillips, 2016-08-17 21:55:01]

lgtm

[robertphillips, 2016-08-17 21:55:06]

The CQ bit was checked by robertphillips@google.com

[commit-bot: I haz the power, 2016-08-17 21:55:10]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-17 21:56:25]

Description was changed from

==========
Fix assert caused by floating point error in tessellating path renderer.

In rare cases, floating point error causes the tesselator to add the
same Vertex to more than one Poly on the same side. This was not a big
problem when we were allocating new vertices when constructing Polys,
but after https://codereview.chromium.org/2029243002 it causes more serious
issues, since each Edge can only belong to two Polys, and violating this
condition messes up the linked list of Edges used for left & right Polys
and the associated estimated vertex count.

The fix is to simply let the first Poly win, and skip that vertex for
subsequent Polys. Since this only occurs in cases where vertices are very
close to each other, it should have little visual effect.

This is also exercised by Nebraska-StateSeal.svg.

BUG=skia:5636
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259493002
==========

to

==========
Fix assert caused by floating point error in tessellating path renderer.

In rare cases, floating point error causes the tesselator to add the
same Vertex to more than one Poly on the same side. This was not a big
problem when we were allocating new vertices when constructing Polys,
but after https://codereview.chromium.org/2029243002 it causes more serious
issues, since each Edge can only belong to two Polys, and violating this
condition messes up the linked list of Edges used for left & right Polys
and the associated estimated vertex count.

The fix is to simply let the first Poly win, and skip that vertex for
subsequent Polys. Since this only occurs in cases where vertices are very
close to each other, it should have little visual effect.

This is also exercised by Nebraska-StateSeal.svg.

BUG=skia:5636
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259493002

Committed:
https://skia.googlesource.com/skia/+/70f5251cc59191040a14cd0f1567aa2129e1f7c6
==========

[commit-bot: I haz the power, 2016-08-17 21:56:26]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/70f5251cc59191040a14cd0f1567aa2129e1f7c6