hashnoise

A custom 2D noise implementation for C++, based on the Improved Noise reference implementation by Ken Perlin.

Instead of a permutation table, the gradient vectors are derived from a hash function, based on an algorithm by Thomas Mueller.

To improve the noise quality for 2D processing, the 16 possible gradient vectors are normalized and evenly distributed around the unit circle.

Advantages

• Easy to seed
• No heap usage if the hash seed is hardcoded
• Pattern only repeats after 2^16 units instead of 2^8
• Smoother gradients for 2D image processing

Interface

The hashnoise::Noise class provides two functions:

double get(double x, double y)

Returns values in [-M_SQRT1_2, M_SQRT1_2] for positive coordinates. The range has been calculated by Rudi Chen.

double getNorm(double x, double y) const

Returns normalized values in [0.0, 1.0] for positive coordinates.

To improve performance, return values are not explicitly clamped. As a result, some values might be slightly out of range, due to the limited accuracy of floating point representation.

Seeds

The hash function uses a multiplier to shuffle bits. This multiplier is provided as a seed to the Noise constructor.

It is non-trivial to find seeds that produce good noise patterns. The included seedsearch tool can help with this task. It generates pseudo-random seeds, uses them to render noise images, and then compresses the images with zlib. The images with the worst compression ratio may be considered reasonably irregular.

In a test with a million random seeds, followed by a manual review, the following seeds turned out most useful:

0x332ff52d 0x0172051a 0x33f9156d 0xb090386a
0x0060adfa 0x131b5961 0x240d6f53 0x4039b8e7
0x48987de7 0x49e61d27 0x55c765f6 0x6ea18f35
0xa317f1ca 0xa6e35365 0xdcb46265 0xf0a91ca9

Install

This is a header-only library. Simply add the header from the include directory to your project.

A test tool is available to render sample images of the noise. It can be compiled and run with:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make
./test/hashnoise-test

In order to compile the seedsearch tool, install zlib and use:

cmake -DCMAKE_BUILD_TYPE=Release -DSEEDSEARCH=ON ..