I was keen on some smooth flowing patterns for an LPD8806 & Arduino project that I have underway, hence I though to myself "Perlin noise" is what I'm after. It's a noise function that gives a very natural looking pattern, it's often used for simulating clouds and so on, invented by Ken Perlin.

So, I found an implementation on the Arduino forums from Mike Edwards (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1191768812) so I tried that. Sadly, it was far too slow. Like 10 ms per LED per colour. I've 96 LEDs on this strip, I'd like to run each one with red, green, and blue, and I want the animation to be smooth, really smooth, so that's a maximum of 50 ms per update. I don't know if this is an efficient implementation of the Perlin noise algorithm or not, but 10 ms per LED isn't going to do the job.

Hence there was some scratching of my head until I came across simplex noise. This was also invented by Ken Perlin. Again, some useful person (Stephen Carmody) had written an implementation (http://stephencarmody.wikispaces.com/Simplex+Noise) in Java, so not much effort to get it up and running on an Arduino. Much faster, under 2 ms per LED per colour. Thus the Arduino can manage ten LEDs and full colour. However, still not good enough if I want to run 96 LEDs.

Further scratching around and I finally twigged to a scheme that might just work - just calculate the simplex noise for a few LEDs and interpolate between them. So, six LEDs controlled by simplex noise, the rest with cubic interpolation to fill in the gaps. The interpolation takes under 0.1 ms per LED so bingo - 96 LEDs with a 50 ms update time.

Here's a video of some test patterns to show the difference in shininess between Perlin, simplex, and simplex with interpolation. I suggest viewing at 720p quality or the video compression induces jumpiness that's not present in reality:

http://youtu.be/vtO0A0CRxo8

Here's the code for the patterns in the video. (I know it's not the most tidy code, sorry.)

- Code: Select all | TOGGLE FULL SIZE
`/*`

Fast and smooth random colour patterns for a LPD8066 addressable RGB LED strip.

By happyinmotion (jez.weston@yahoo.com)

Simplex noise code taken from Stephen Carmody's Java implementation at:

http://stephencarmody.wikispaces.com/Simplex+Noise

Perlin Noise code copyright 2007 Mike Edwards:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1191768812

// Timing results on a 96 LED strip controlled by an Arduino Nano v3:

// Perlin noise - 10 ms per LED per colour

// Simplex noise - 1 ms per LED per colour

// Cubic interpolation - 0.02 ms per LED per colour

//

// Smooth motion needs a refresh every 50 ms or so. For a 96 RGB LED strip, I used 6 simplex nodes with interpolation between to get it all smoothly flowing.

*/

// LPD8806-based code from Adafruit for RGB LED Modules in a strip

/*****************************************************************************/

// you can also use hardware SPI, for ultra fast writes by leaving out the

// data and clock pin arguments. This will 'fix' the pins to the following:

// on Arduino 168/328 thats data = 11, and clock = pin 13.

#include "LPD8806.h"

#include "SPI.h"

// Strip variables:

const int LEDs_in_strip = 96;

const int LEDs_for_simplex = 6;

// Extra fake LED at the end, to avoid fencepost problem.

// It is used by simplex node and interpolation code.

float LED_array_red[LEDs_in_strip+1];

float LED_array_green[LEDs_in_strip+1];

float LED_array_blue[LEDs_in_strip+1];

float LED_array_hue[LEDs_in_strip+1];

float LED_array_brightness[LEDs_in_strip+1];

int node_spacing = LEDs_in_strip / LEDs_for_simplex;

LPD8806 strip = LPD8806(LEDs_in_strip);

// Perlin noise global variables:

float x1,y1,x2,y2;

// Set up Perlin globals:

//persistence affects the degree to which the "finer" noise is seen

float persistence = 0.25;

//octaves are the number of "layers" of noise that get computed

int octaves = 3;

// Simplex noise global variables:

int i, j, k, A[] = {0, 0, 0};

float u, v, w, s;

static float onethird = 0.333333333;

static float onesixth = 0.166666667;

int T[] = {0x15, 0x38, 0x32, 0x2c, 0x0d, 0x13, 0x07, 0x2a};

// Simplex noise parameters:

// Useable values for time increment range from 0.005 (barely perceptible) to 0.2 (irritatingly flickery)

// 0.02 seems ideal for relaxed screensaver

float timeinc = 0.02;

// Useable values for space increment range from 0.8 (LEDS doing different things to their neighbours), to 0.02 (roughly one feature present in 15 LEDs).

// 0.05 seems ideal for relaxed screensaver

float spaceinc = 0.1;

// Simplex noise variables:

// So that subsequent calls to SimplexNoisePattern produce similar outputs, this needs to be outside the scope of loop()

float yoffset = 0.0;

float saturation = 1.0;

void setup()

{

// Start up the LED strip

strip.begin();

// Update the strip, to start they are all 'off'

strip.show();

Serial.begin(9600);

Serial.println("Setup done ");

}

void loop() {

int repeats = 200;

// Perlin noise for five red LEDs

timeinc = 0.1;

for ( int i=0; i<repeats; i++ ) {

PerlinNoisePattern( 5 );

yoffset += timeinc;

}

AllOff();

delay(500);

// Simplex noise for ten full-colour LEDs

// No interpolation.

timeinc = 0.02;

for ( int i=0; i<repeats; i++ ) {

SimplexNoisePattern( spaceinc, timeinc, yoffset, 10);

yoffset += timeinc;

}

AllOff();

delay(500);

// Simplex noise for whole strip of 96 LEDs.

// (Well, it's simplex noise for 6 LEDs and cubic interpolation between those nodes.)

for ( int i=0; i<repeats; i++ ) {

SimplexNoisePatternInterpolated( spaceinc, timeinc, yoffset);

yoffset += timeinc;

}

AllOff();

delay(500);

}

void PerlinNoisePattern(int numLEDs) {

float xoffset = 1.0;

for (int j=0; j < numLEDs; j++) {

xoffset += spaceinc;

// Caluclate Perlin Noise (range -1 to 1), expand and bias that range:

// Takes around 10 ms per call, so only doing this for the red LEDs, not full colour

int r = int(PerlinNoise2(xoffset,yoffset,persistence,octaves)*196+32);

// Clip output to the brightness level of 0-127 that the LED strip accepts.

// Doing this with constrain() is slooow. Doing this explicitly adds no time at all. Conclusion: constrain() sucks.

if ( r>127 ) { r=127; }

else if ( r<0 ) { r=0; }

strip.setPixelColor(j, r, 0, 0);

}

strip.show();

}

void SimplexNoisePattern( float spaceinc, float timeinc, float yoffset, int numLEDs) {

// Calculate simplex noise for LEDs that are nodes:

// Store raw values from simplex function (-0.347 to 0.347)

float xoffset = 0.0;

for (int i=0; i<numLEDs; i++) {

xoffset += spaceinc;

LED_array_red[i] = SimplexNoise(xoffset,yoffset,0);

LED_array_green[i] = SimplexNoise(xoffset,yoffset,1);

LED_array_blue[i] = SimplexNoise(xoffset,yoffset,2);

}

// Convert values from raw noise to scaled r,g,b and feed to strip.

// Raw noise is -0.347 to +0.347 or thereabouts.

for (int i=0; i<numLEDs; i++) {

int r = int(LED_array_red[i]*403 + 16);

int g = int(LED_array_green[i]*403 + 16);

int b = int(LED_array_blue[i]*403 + 16);

if ( r>127 ) { r=127; }

else if ( r<0 ) { r=0; } // Adds no time at all. Conclusion: constrain() sucks.

if ( g>127 ) { g=127; }

else if ( g<0 ) { g=0; }

if ( b>127 ) { b=127; }

else if ( b<0 ) { b=0; }

strip.setPixelColor(i, r, g, b);

}

// Update strip

strip.show();

}

void SimplexNoisePatternInterpolated( float spaceinc, float timeinc, float yoffset) {

// Calculate simplex noise for LEDs that are nodes:

// Store raw values from simplex function (-0.347 to 0.347)

float xoffset = 0.0;

for (int i=0; i<=LEDs_in_strip; i=i+node_spacing) {

xoffset += spaceinc;

LED_array_red[i] = SimplexNoise(xoffset,yoffset,0);

LED_array_green[i] = SimplexNoise(xoffset,yoffset,1);

LED_array_blue[i] = SimplexNoise(xoffset,yoffset,2);

}

// Interpolate values for LEDs between nodes

for (int i=0; i<LEDs_in_strip; i++) {

int position_between_nodes = i % node_spacing;

int last_node, next_node;

// If at node, skip

if ( position_between_nodes == 0 ) {

// At node for simplex noise, do nothing but update which nodes we are between

last_node = i;

next_node = last_node + node_spacing;

}

// Else between two nodes, so identify those nodes

else {

// And interpolate between the values at those nodes for red, green, and blue

float t = float(position_between_nodes) / float(node_spacing);

float t_squaredx3 = 3*t*t;

float t_cubedx2 = 2*t*t*t;

LED_array_red[i] = LED_array_red[last_node] * ( t_cubedx2 - t_squaredx3 + 1.0 ) + LED_array_red[next_node] * ( -t_cubedx2 + t_squaredx3 );

LED_array_green[i] = LED_array_green[last_node] * ( t_cubedx2 - t_squaredx3 + 1.0 ) + LED_array_green[next_node] * ( -t_cubedx2 + t_squaredx3 );

LED_array_blue[i] = LED_array_blue[last_node] * ( t_cubedx2 - t_squaredx3 + 1.0 ) + LED_array_blue[next_node] * ( -t_cubedx2 + t_squaredx3 );

}

}

// Convert values from raw noise to scaled r,g,b and feed to strip

for (int i=0; i<LEDs_in_strip; i++) {

int r = int(LED_array_red[i]*403 + 16);

int g = int(LED_array_green[i]*403 + 16);

int b = int(LED_array_blue[i]*403 + 16);

if ( r>127 ) { r=127; }

else if ( r<0 ) { r=0; } // Adds no time at all. Conclusion: constrain() sucks.

if ( g>127 ) { g=127; }

else if ( g<0 ) { g=0; }

if ( b>127 ) { b=127; }

else if ( b<0 ) { b=0; }

strip.setPixelColor(i, r, g, b);

}

// Update strip

strip.show();

}

/*****************************************************************************/

// Simplex noise code:

// From an original algorythm by Ken Perlin.

// Returns a value in the range of about [-0.347 .. 0.347]

float SimplexNoise(float x, float y, float z) {

// Skew input space to relative coordinate in simplex cell

s = (x + y + z) * onethird;

i = fastfloor(x+s);

j = fastfloor(y+s);

k = fastfloor(z+s);

// Unskew cell origin back to (x, y , z) space

s = (i + j + k) * onesixth;

u = x - i + s;

v = y - j + s;

w = z - k + s;;

A[0] = A[1] = A[2] = 0;

// For 3D case, the simplex shape is a slightly irregular tetrahedron.

// Determine which simplex we're in

int hi = u >= w ? u >= v ? 0 : 1 : v >= w ? 1 : 2;

int lo = u < w ? u < v ? 0 : 1 : v < w ? 1 : 2;

return k_fn(hi) + k_fn(3 - hi - lo) + k_fn(lo) + k_fn(0);

}

int fastfloor(float n) {

return n > 0 ? (int) n : (int) n - 1;

}

float k_fn(int a) {

s = (A[0] + A[1] + A[2]) * onesixth;

float x = u - A[0] + s;

float y = v - A[1] + s;

float z = w - A[2] + s;

float t = 0.6f - x * x - y * y - z * z;

int h = shuffle(i + A[0], j + A[1], k + A[2]);

A[a]++;

if (t < 0) return 0;

int b5 = h >> 5 & 1;

int b4 = h >> 4 & 1;

int b3 = h >> 3 & 1;

int b2 = h >> 2 & 1;

int b = h & 3;

float p = b == 1 ? x : b == 2 ? y : z;

float q = b == 1 ? y : b == 2 ? z : x;

float r = b == 1 ? z : b == 2 ? x : y;

p = b5 == b3 ? -p : p;

q = b5 == b4 ? -q: q;

r = b5 != (b4^b3) ? -r : r;

t *= t;

return 8 * t * t * (p + (b == 0 ? q + r : b2 == 0 ? q : r));

}

int shuffle(int i, int j, int k) {

return b(i, j, k, 0) + b(j, k, i, 1) + b(k, i, j, 2) + b(i, j, k, 3) + b(j, k, i, 4) + b(k, i, j, 5) + b(i, j, k, 6) + b(j, k, i, 7);

}

int b(int i, int j, int k, int B) {

return T[b(i, B) << 2 | b(j, B) << 1 | b(k, B)];

}

int b(int N, int B) {

return N >> B & 1;

}

/*****************************************************************************/

// Perlin noise code:

// using the algorithm from http://freespace.banned.net/hugo.elias/models/m_perlin.html

// thanks to hugo elias

float Noise2(float x, float y)

{

long noise;

noise = x + y * 57;

noise = (noise << 13) ^ noise;

return ( 1.0 - ( long(noise * (noise * noise * 15731L + 789221L) + 1376312589L) & 0x7fffffff) / 1073741824.0);

}

float SmoothNoise2(float x, float y)

{

float corners, sides, center;

corners = ( Noise2(x-1, y-1)+Noise2(x+1, y-1)+Noise2(x-1, y+1)+Noise2(x+1, y+1) ) / 16;

sides = ( Noise2(x-1, y) +Noise2(x+1, y) +Noise2(x, y-1) +Noise2(x, y+1) ) / 8;

center = Noise2(x, y) / 4;

return (corners + sides + center);

}

float InterpolatedNoise2(float x, float y)

{

float v1,v2,v3,v4,i1,i2,fractionX,fractionY;

long longX,longY;

longX = long(x);

fractionX = x - longX;

longY = long(y);

fractionY = y - longY;

v1 = SmoothNoise2(longX, longY);

v2 = SmoothNoise2(longX + 1, longY);

v3 = SmoothNoise2(longX, longY + 1);

v4 = SmoothNoise2(longX + 1, longY + 1);

i1 = Interpolate(v1 , v2 , fractionX);

i2 = Interpolate(v3 , v4 , fractionX);

return(Interpolate(i1 , i2 , fractionY));

}

float Interpolate(float a, float b, float x)

{

//cosine interpolations

return(CosineInterpolate(a, b, x));

}

float LinearInterpolate(float a, float b, float x)

{

return(a*(1-x) + b*x);

}

float CosineInterpolate(float a, float b, float x)

{

float ft = x * 3.1415927;

float f = (1 - cos(ft)) * .5;

return(a*(1-f) + b*f);

}

float PerlinNoise2(float x, float y, float persistance, int octaves)

{

float frequency, amplitude;

float total = 0.0;

for (int i = 0; i <= octaves - 1; i++)

{

frequency = pow(2,i);

amplitude = pow(persistence,i);

total = total + InterpolatedNoise2(x * frequency, y * frequency) * amplitude;

}

return(total);

}

void AllOff() {

// Reset LED strip

strip.begin();

strip.show();

}

I'd love to see a library for the LPD8806 & Arduino combination that includes as many shiny algorithms as possible. Here's simplex, but I'd also love to see some reaction-diffusion patterns and whatever else people can think of. I'm slowly working away at some more ideas (as well as working on the hardware for this project) and I'm happy to share the implementations, but there seems to be enough people using the LPD8806 & Arduino combination that a library could help all of us.