Fix SkRadialGradient center discontinuity

Fix SkRadialGradient center discontinuity

(AKA let's slow down radial gradients!)

Avoid discontinuities when r ~= 0.

BUG=skia:5052
R=reed@google.com,mtklein@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1753133003

Committed: https://skia.googlesource.com/skia/+/0032a302ca8cddc7f6ca500b8096afa4888fc614

[f(malita), 2016-03-02 17:26:33]

Description was changed from

==========
Fix SkRadialGradient center discontinuity

(AKA let's slow down radial gradients!)

Avoid discontinuities when r ~= 0.

BUG=skia:5052
R=reed@google.com,mtklein@google.com
==========

to

==========
Fix SkRadialGradient center discontinuity

(AKA let's slow down radial gradients!)

Avoid discontinuities when r ~= 0.

BUG=skia:5052
R=reed@google.com,mtklein@google.com
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

[f(malita), 2016-03-02 17:34:08]

This is what I think the fix for
https://bugs.chromium.org/p/skia/issues/detail?id=5052 looks like.

Unfortunately it slows raster clamped radials by ~7%.  So I'm not sure we should
land it in its current form.  Maybe something to keep in mind when rewriting
radials for shadeSpan4f.

[f(malita), 2016-03-02 17:34:21]

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

[commit-bot: I haz the power, 2016-03-02 17:34:30]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1753133003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1753133003/1

[mtklein, 2016-03-02 17:38:31]

lgtm

[commit-bot: I haz the power, 2016-03-02 17:48:34]

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

[commit-bot: I haz the power, 2016-03-02 17:48:37]

Dry run: This issue passed the CQ dry run.

[f(malita), 2016-03-03 15:32:12]

Updated based on MikeR's idea to use a nearly-zero clamp and avoid the full
blown sqrt.

This leaves R * R.rsqrt() alone => slowdown is now 1-1.5%.

PTAL

[f(malita), 2016-03-03 15:32:22]

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

[commit-bot: I haz the power, 2016-03-03 15:32:29]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1753133003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1753133003/20001

[commit-bot: I haz the power, 2016-03-03 15:55:24]

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

[commit-bot: I haz the power, 2016-03-03 15:55:25]

Dry run: This issue passed the CQ dry run.

[mtklein, 2016-03-03 16:48:51]

still lgtm.  good idea

[f(malita), 2016-03-04 14:28:40]

The CQ bit was checked by fmalita@chromium.org

[commit-bot: I haz the power, 2016-03-04 14:28:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1753133003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1753133003/20001

[commit-bot: I haz the power, 2016-03-04 14:29:37]

Description was changed from

==========
Fix SkRadialGradient center discontinuity

(AKA let's slow down radial gradients!)

Avoid discontinuities when r ~= 0.

BUG=skia:5052
R=reed@google.com,mtklein@google.com
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

to

==========
Fix SkRadialGradient center discontinuity

(AKA let's slow down radial gradients!)

Avoid discontinuities when r ~= 0.

BUG=skia:5052
R=reed@google.com,mtklein@google.com
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...

Committed:
https://skia.googlesource.com/skia/+/0032a302ca8cddc7f6ca500b8096afa4888fc614
==========

[commit-bot: I haz the power, 2016-03-04 14:29:38]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/0032a302ca8cddc7f6ca500b8096afa4888fc614