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@google.com, sugoi
TBR=senorblanco
Author: senorblanco@chromium.org
Review URL: https://codereview.chromium.org/332523006
Enabling Perlin Noise on Android
I enabled the Perlin Noise shader on Android after doing some minor modifications to the shader, specifically for Android (and #ifdefed for Android, to make sure none of this affects other platforms).
For Tegra devices (Nexus 7, Xoom), a precision issue related to the color values read from textures caused the noise to read the wrong indices and produce bad noise. I fixed this by adding a founding of the values read by simply doing the equivalent of "colorValue = floor(colorValue * 255.0) / 255.0" to make sure we retrieve the colors that were written in the texture originally.
For non-Tegra devices (Nexus 10), dealing with values in the order of 4096.0 was problematic without using the "highp" precision setting. To solve this, a few variables were given the high precision setting.
Since both fixes don't seem to do considerable harm to the platforms that are not being targetted, I left both fixes on all android devices for now.
I also reduced the Perlin noise gm so that it takes less time to test it on the Xoom (Original time was about 20 seconds, this shold take less than 10, hopefully)
BUG=
R=senorblanco@google.com, bsalomon@google.com, sugoi@google.com, senorblanco@chromium.org
Author: sugoi@chromium.org
Review URL: https://chromiumcodereview.appspot.com/16818013
git-svn-id: http://skia.googlecode.com/svn/trunk@9637 2bbb7eff-a529-9590-31e7-b0007b416f81
1 ) Added GPU simplex noise as a comparison to GPU Perlin noise. It can be enabled simply by using a #define (SK_USE_SIMPLEX_NOISE)
2 ) Enabled GPU Perlin noise tests
3 ) Added a small benchmark for noise
4 ) Disabled GPU Perlin noise on Android based on benchmarks
Review URL: https://codereview.chromium.org/14087002
git-svn-id: http://skia.googlecode.com/svn/trunk@8719 2bbb7eff-a529-9590-31e7-b0007b416f81
