fix path op conic bugs

More conic-specific tests revealed a few conic-specific bugs. Because javascript / canvas make visualizing conics tricky, new native tools are required.

The utility SubsetPath removes parts of a potentially very large path to isolate a minimal test case. SubsetPath is very useful for debugging path ops, but is not path ops specific.

PathOpsBuilderConicTest compares the output of the Path Ops Builder, sequential calls to Simplify, and SkRegions for some number of rotated ovals.

Some tests caused path ops to hang. It was caught adding a loop of curves because the head was not found by the tail. Even though the root cause has been fixed, SkSegment::addCurveTo callers now abort the path op if the same curve was added twice.

The subdivided conic weight was been computed anew. Fortunately, it's a simpler computation that the one it replaces.

Some Simplify() subroutines returned false to signal that the results needed assembling. Change these to abort the current operation instead.

Coincident curve intersection triggered two small bugs; one where no perpendicular could be found for coincident curves, and one where no coincident curves remain after looping.

The SixtyOvals test can be run through multiple processes instead of multiple threads. This strategy allows a 48 core machine to saturate all cores at 100%.

The DEBUG_VISUALIZE_CONICS code in PathOpsConicIntersectionTest acknowleges that it is easier to visualize conics with Skia than with script and html canvas. This test also verifies that path ops subdivision matches geometry chopping.

TBR=reed@google.com

Committed: https://skia.googlesource.com/skia/+/ef784fb7f58c9c021172045a8e0b396c81fdc425

[caryclark, 2015-10-30 18:37:47]

Description was changed from

==========
test class to isolate problematic part of complex paths

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

to

==========
More conic-specific tests revealed a few conic-specific bugs. Because javascript
/ canvas make visualizing conics tricky, new native tools are required.

The utility SubsetPath removes parts of a potentially very large path to isolate
a minimal test case. SubsetPath is very useful for debugging path ops, but is
not path ops specific.

PathOpsBuilderConicTest compares the output of the Path Ops Builder, sequential
calls to Simplify, and SkRegions for some number of rotated ovals.

Some tests caused path ops to hang. It was caught adding a loop of curves
because the head was not found by the tail. Even though the root cause has been
fixed, SkSegment::addCurveTo callers now abort the path op if the same curve was
added twice.

The subdivided conic weight was been computed anew. Fortunately, it's a simpler
computation that the one it replaces.

Some Simplify() subroutines returned false to signal that the results needed
assembling. Change these to abort the current operation instead.

Coincident curve intersection triggered two small bugs; one where no
perpendicular could be found for coincident curves, and one where no coincident
curves remain after looping.

The SixtyOvals test can be run through multiple processes instead of multiple
threads. This strategy allows a 48 core machine to saturate all cores at 100%.

The DEBUG_VISUALIZE_CONICS code in PathOpsConicIntersectionTest acknowleges that
it is easier to visualize conics with Skia than with script and html canvas.
This test also verifies that path ops subdivision matches geometry chopping.

TBR=reed@google.com
==========

[caryclark, 2015-10-30 18:39:15]

The CQ bit was checked by caryclark@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-10-30 18:39:23]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405383004/120001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405383004/120001

[commit-bot: I haz the power, 2015-10-30 18:40:15]

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

[commit-bot: I haz the power, 2015-10-30 18:40:16]

Dry run: Try jobs failed on following builders:
  Build-Ubuntu-Clang-x86_64-Debug-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-Clang-x...)
  Build-Ubuntu-GCC-Arm64-Debug-Android-Trybot on client.skia.compile
(JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-Arm...)
  Build-Ubuntu-GCC-Arm7-Debug-Android-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-Arm...)
  Build-Ubuntu-GCC-Mips-Debug-Android-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-Mip...)
  Build-Ubuntu-GCC-x86_64-Release-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-x86...)

[caryclark, 2015-10-30 18:46:29]

The CQ bit was checked by caryclark@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-10-30 18:46:39]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405383004/140001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405383004/140001

[commit-bot: I haz the power, 2015-10-30 18:47:35]

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

[commit-bot: I haz the power, 2015-10-30 18:47:36]

Dry run: Try jobs failed on following builders:
  Build-Ubuntu-Clang-x86_64-Debug-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-Clang-x...)
  Build-Ubuntu-GCC-Arm7-Debug-Android-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-Arm...)
  Build-Ubuntu-GCC-Mips-Debug-Android-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-Mip...)
  Build-Ubuntu-GCC-x86_64-Release-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-x86...)

[caryclark, 2015-10-30 18:50:21]

The CQ bit was checked by caryclark@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-10-30 18:50:29]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405383004/160001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405383004/160001

[commit-bot: I haz the power, 2015-10-30 19:01:38]

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

[commit-bot: I haz the power, 2015-10-30 19:01:39]

Dry run: This issue passed the CQ dry run.

[caryclark, 2015-10-30 19:02:07]

The CQ bit was checked by caryclark@google.com

[commit-bot: I haz the power, 2015-10-30 19:02:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405383004/160001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405383004/160001

[commit-bot: I haz the power, 2015-10-30 19:03:11]

Committed patchset #9 (id:160001) as
https://skia.googlesource.com/skia/+/ef784fb7f58c9c021172045a8e0b396c81fdc425