Use correct gradient calculation for rotated distance fields.

Use correct gradient calculation for rotated distance fields.

For all uniform scaled matrices, we were using the y coordinate of the
y-direction gradient of the v texel space coordinate to scale the
distance values. The problem is, if you rotate by 90 degrees this value
becomes 0. The correct answer is to take the length of the y-direction
gradient.

BUG=skia:4864
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1776383002

Committed: https://skia.googlesource.com/skia/+/cf371bb41b4a0591347a076ce7d83336d4bbc6fb

[jvanverth1, 2016-03-09 19:37:44]

Description was changed from

==========
Use correct gradient calculation for rotated distance fields.

For all uniform scaled matrices, we were using the y coordinate of the
y-direction gradient of the v texel space coordinate to scale the
distance values. The problem is, if you rotate by 90 degrees this value
becomes 0. The correct answer is to take the length of the y-direction
gradient.

BUG=skia:4864
==========

to

==========
Use correct gradient calculation for rotated distance fields.

For all uniform scaled matrices, we were using the y coordinate of the
y-direction gradient of the v texel space coordinate to scale the
distance values. The problem is, if you rotate by 90 degrees this value
becomes 0. The correct answer is to take the length of the y-direction
gradient.

BUG=skia:4864
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

[jvanverth1, 2016-03-09 19:40:09]

jvanverth@google.com changed reviewers:
+ bsalomon@google.com, joshualitt@google.com

[jvanverth1, 2016-03-09 19:40:09]

I've separated the pure uniform scale case from the uniform scale + rotation
case, as the former's shader is a little simpler. However, this will break
batching. I believe it's still a win as we'll mostly see non-rotated uniform
scale of small paths and text.

[bsalomon, 2016-03-10 15:38:36]

lgtm

[jvanverth1, 2016-03-10 15:46:32]

The CQ bit was checked by jvanverth@google.com

[commit-bot: I haz the power, 2016-03-10 15:46:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1776383002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1776383002/1

[commit-bot: I haz the power, 2016-03-10 15:47:51]

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

[commit-bot: I haz the power, 2016-03-10 15:47:52]

Try jobs failed on following builders:
  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...)

[jvanverth1, 2016-03-10 18:55:10]

The CQ bit was checked by jvanverth@google.com

[jvanverth1, 2016-03-10 18:55:11]

The patchset sent to the CQ was uploaded after l-g-t-m from bsalomon@google.com
Link to the patchset: https://codereview.chromium.org/1776383002/#ps20001
(title: "Fix android error")

[commit-bot: I haz the power, 2016-03-10 18:55:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1776383002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1776383002/20001

[commit-bot: I haz the power, 2016-03-10 19:10:45]

Description was changed from

==========
Use correct gradient calculation for rotated distance fields.

For all uniform scaled matrices, we were using the y coordinate of the
y-direction gradient of the v texel space coordinate to scale the
distance values. The problem is, if you rotate by 90 degrees this value
becomes 0. The correct answer is to take the length of the y-direction
gradient.

BUG=skia:4864
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

to

==========
Use correct gradient calculation for rotated distance fields.

For all uniform scaled matrices, we were using the y coordinate of the
y-direction gradient of the v texel space coordinate to scale the
distance values. The problem is, if you rotate by 90 degrees this value
becomes 0. The correct answer is to take the length of the y-direction
gradient.

BUG=skia:4864
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...

Committed:
https://skia.googlesource.com/skia/+/cf371bb41b4a0591347a076ce7d83336d4bbc6fb
==========

[commit-bot: I haz the power, 2016-03-10 19:10:46]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/cf371bb41b4a0591347a076ce7d83336d4bbc6fb