Add a clamp stage to SkRasterPipelineBlitter.

Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

So we don't double-clamp, I've added a _noclamp version of sk_linear_to_srgb()
that simply asserts a clamp isn't necessary.  This happens to expose the Sk4f
_needs_trunc version that might be useful for power users (*cough* Matt *cough*).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002

Committed: https://skia.googlesource.com/skia/+/b5acf6e702e318b405a04d38bfdac602dc3ed773

[mtklein_C, 2016-07-23 19:06:19]

Description was changed from

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

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

to

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002
==========

[mtklein_C, 2016-07-23 19:06:49]

Description was changed from

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002
==========

to

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

So we don't double-clamp, I've added a _noclamp version of sk_linear_to_srgb()
that simply asserts a clamp isn't necessary.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002
==========

[mtklein_C, 2016-07-23 19:15:37]

Description was changed from

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

So we don't double-clamp, I've added a _noclamp version of sk_linear_to_srgb()
that simply asserts a clamp isn't necessary.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002
==========

to

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

So we don't double-clamp, I've added a _noclamp version of sk_linear_to_srgb()
that simply asserts a clamp isn't necessary.  This happens to expose the Sk4f
_needs_trunc version that might be useful for power users (*cough* Matt
*cough*).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002
==========

[mtklein_C, 2016-07-23 19:17:41]

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

[commit-bot: I haz the power, 2016-07-23 19:17:49]

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

[mtklein_C, 2016-07-23 19:36:13]

mtklein@chromium.org changed reviewers:
+ msarett@google.com, reed@google.com

[commit-bot: I haz the power, 2016-07-23 19:36:22]

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

[commit-bot: I haz the power, 2016-07-23 19:36:23]

Dry run: This issue passed the CQ dry run.

[mtklein_C, 2016-07-24 22:05:58]

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

[commit-bot: I haz the power, 2016-07-24 22:06:01]

Dry run: 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, 2016-07-24 22:23:11]

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

[commit-bot: I haz the power, 2016-07-24 22:23:12]

Dry run: This issue passed the CQ dry run.

[msarett, 2016-07-25 13:12:07]

lgtm

[mtklein, 2016-07-25 13:12:28]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2016-07-25 13:12:34]

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, 2016-07-25 13:13:50]

Description was changed from

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

So we don't double-clamp, I've added a _noclamp version of sk_linear_to_srgb()
that simply asserts a clamp isn't necessary.  This happens to expose the Sk4f
_needs_trunc version that might be useful for power users (*cough* Matt
*cough*).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002
==========

to

==========
Add a clamp stage to SkRasterPipelineBlitter.

This clamps to [0,1] premul just before every store to memory.

By making the clamp a stage itself, this design makes it easy to move the clamp
around, to replace it with a debug-only assert-we're-clamped stage for certain
formats, clamp in more places, programatically not clamp, etc. etc.

Before this change, clamping was a little haphazard: store_srgb clamped
R, G and B to [0,1], but not A, and didn't clamp the colors to A.  565
didn't clamp at all.

6 GMs draw subtly differently in sRGB, I think because we've started clamping
colors to alpha to enforce premultiplication better.  No changes for 565.

My hope is that now no other stage need ever concern itself with clamping.

So we don't double-clamp, I've added a _noclamp version of sk_linear_to_srgb()
that simply asserts a clamp isn't necessary.  This happens to expose the Sk4f
_needs_trunc version that might be useful for power users (*cough* Matt
*cough*).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178793002

Committed:
https://skia.googlesource.com/skia/+/b5acf6e702e318b405a04d38bfdac602dc3ed773
==========

[commit-bot: I haz the power, 2016-07-25 13:13:51]

Committed patchset #4 (id:60001) as
https://skia.googlesource.com/skia/+/b5acf6e702e318b405a04d38bfdac602dc3ed773