Fix tiled perlin noise.

Fix tiled perlin noise.

It turns out that the perlin implementation we inherited from WebKit
does not actually generate tileable noise (see Chromium bug
http://crbug.com/383495).

The main problem is that when generating coordinates for gradient
interpolation, it was attempting to wrap both x and (x + 1)
simultaneously at the tile boundary (that is, either both or neither
are wrapped). This obviously won't work, since along the tile seams,
(x + 1) should be wrapped, but x should not. The same is true in y.

This patch fixes both the CPU and GPU paths, renames some variables to
more closely match the spec, and modifies the perlin noise GM to
actually test tiling. (Note that the clipping the GM was doing was
removed, since it's superfluous: it used to be necessary for image
filters, but isn't anymore, and this isn't an image filter GM anyway.)

R=sugoi
TBR=senorblanco

Committed: https://skia.googlesource.com/skia/+/ce6a354e121915c2925e545e7df2929492d69d50

[Stephen White, 2014-06-12 16:20:01]

sugoi: PTAL. Thanks!

[sugoi, 2014-06-12 17:19:53]

LGTM with one minor comment.

https://codereview.chromium.org/332523006/diff/20001/src/effects/SkPerlinNois...
File src/effects/SkPerlinNoiseShader.cpp (right):

https://codereview.chromium.org/332523006/diff/20001/src/effects/SkPerlinNois...
src/effects/SkPerlinNoiseShader.cpp:1030: noiseCode.appendf("\tvec2 %s =
fract(%s.xy);\n", fractVal, noiseVec);
noiseVec is already a vec2, I think, so I think you can skip the ".xy" here

[Stephen White, 2014-06-12 17:37:18]

https://codereview.chromium.org/332523006/diff/20001/src/effects/SkPerlinNois...
File src/effects/SkPerlinNoiseShader.cpp (right):

https://codereview.chromium.org/332523006/diff/20001/src/effects/SkPerlinNois...
src/effects/SkPerlinNoiseShader.cpp:1030: noiseCode.appendf("\tvec2 %s =
fract(%s.xy);\n", fractVal, noiseVec);
On 2014/06/12 17:19:53, sugoi wrote:
> noiseVec is already a vec2, I think, so I think you can skip the ".xy" here

Good catch! Done.

[Stephen White, 2014-06-12 17:50:32]

The CQ bit was checked by senorblanco@chromium.org

[commit-bot: I haz the power, 2014-06-12 17:50:52]

CQ is trying da patch. Follow status at

https://skia-tree-status.appspot.com/cq/senorblanco@chromium.org/332523006/40001

[commit-bot: I haz the power, 2014-06-12 17:50:53]

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

[commit-bot: I haz the power, 2014-06-12 17:50:54]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Stephen White, 2014-06-12 17:53:06]

The CQ bit was checked by senorblanco@chromium.org

[commit-bot: I haz the power, 2014-06-12 17:53:52]

CQ is trying da patch. Follow status at

https://skia-tree-status.appspot.com/cq/senorblanco@chromium.org/332523006/40001

[commit-bot: I haz the power, 2014-06-12 17:53:53]

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

[commit-bot: I haz the power, 2014-06-12 17:53:54]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Stephen White, 2014-06-12 17:56:44]

The CQ bit was checked by senorblanco@chromium.org

[commit-bot: I haz the power, 2014-06-12 17:57:52]

CQ is trying da patch. Follow status at

https://skia-tree-status.appspot.com/cq/senorblanco@chromium.org/332523006/40001

[commit-bot: I haz the power, 2014-06-12 18:24:25]

Change committed as ce6a354e121915c2925e545e7df2929492d69d50