openFrameworks has a built-in implementation of simplex noise, implemented in the ofNoise( t ) function. For example, the following code draws the Perlin noise function, ofNoise( t ), for t ranging from 0 to 10 on the screen:

ofSetColor( 0, 0, 0 );	
for (int x=0; x<1000; x++) {
  float t = x * 0.01;
  float y = ofNoise( t );
  ofLine( x, 300, x, 300 - y * 300 );
}

Run the code and you will see the following graph:

Now replace the line float y = ofNoise( t ); with the following line:

float y = ofNoise( t + 493.0 );

This code renders the noise function in the range [443, 453].

Considering the preceding graphs, you can note the following properties:

You can use this function for randomly changing some parameters of the objects in your project; for example, position, size, or angle. Normally, we don't use the pure ofNoise( t ) function, but a more complex formula.

float value = amplitude * ofNoise( timePosition + position0 );

Here, amplitude defines the output range of the value, namely [0, amplitude]; position0 is a constant (for example, random); and timePosition is a value that increases with time.

See a simple example of the implementation of this idea for controlling sound volumes in The singing voices example section in Chapter 6, Working with Sounds. Using Perlin noise for creating a knot curve and changing its color is shown in The twisting knot example section in Chapter 7, Drawing in 3D.

Another interesting example is drawing a cloud of a hundred randomly flying points. It can be done with the following code:

ofSetColor( 0, 0, 0 );
float time = ofGetElapsedTimef();
for (int i=0; i<100; i++) {
  float ampX = ofGetWidth();
  float ampY = ofGetHeight();
  float speed = 0.1;
  float posX0 = i * 104.3 + 14.6;
  float posY0 = i * 53.3 + 35.2;
  float x = ampX * ofNoise( time * speed + posX0 );
  float y = ampY * ofNoise( time * speed + posY0 );
  ofCircle( x, y, 10 );
}

Here, constants 104.3, 14.6, 53.3, and 35.2 were chosen quite arbitrarily—just to obtain distinct values for posX0 and posY0. On running this, you will see a cloud of slowly flying points:

See the further evolution of this example in the Dancing cloud example section in Chapter 6, Working with Sounds.

By summing up several Perlin noises with different scales, it is possible to obtain more interesting noises. See the openFrameworks example in the openFrameworks' folder examples/math/noise1dOctaveExample. It sums up several noises and you can see the resultant function.

Now we will see how to use multidimensional Perlin noise for generating textures and other fields.