spiralnegative - a blog about random stuff I like

Generative art, sometimes called algorithmic art, is defined by Wikipedia as “art that in whole or in part has been created with the use of an autonomous system (…) [which] can independently determine features of an artwork that would otherwise require decisions made directly by the artist”. Back in my second year at university I studied Grammars for Generative Art which introduced its visual aspect to me. Many years have passed since then and I have only recently started experimenting with it again after browsing /r/generative.

Context Free

Context Free is a digital art program that generates images from instructions in the form of context free (design) grammar called cfdg files. What a context free grammar typically does is to analyze a sentence of symbols to see if they can reduce to some root symbol. Here the symbol is a shape, composed of some number of primitive shapes (squares, circles, triangles and fills) and non-primitive shapes. A cfdg file consists of startshape and some number of shape rules. These rules provide information about the shape - colour, geometry (position, size, rotation and skew) and Z order (for overlapping shapes).

Example 1

Here is an example of an image with two primitive shapes. The startshape is called BRANCH but you can use any name. Note that at least one shape with the same name should be provided, otherwise Shape with no rules encountered warning will be displayed. The two shapes are a triangle and a circle. The first one has hue equal to 160, brightness 0.8 and saturation 1. The second has hue 250, brightness 1 and saturation 0.1 but it’s also moved horizontally (x) by 2 and vertically (y) by 1.

startshape BRANCH

shape BRANCH
{
  TRIANGLE [h 160 b 0.8 sat 1]
  CIRCLE [h 250 b 1 sat 0.1 x 2 y 1]
}

Example 2

The example above demonstrates that rules tell Context Free how to draw a shape in terms of other shapes. When a shape is drawn, its rule is evaluated and the shape is replaced with the shapes listed in the rule. Each replacement has a state, relative to the state of the parent shape. This can be illustrated with a simple recursion. The BRANCH shape contains the triangle from the previous example and a call to the same BRANCH rule with parameters. On each call size changes by 0.9, y by -0.2, alpha by -0.2 and hue by 8. Note that the order of the parameters does not change how the shape is drawn.

startshape BRANCH

shape BRANCH
{
  TRIANGLE [h 160 b 0.8 sat 1]
  BRANCH [s 0.9 y -0.2 a -0.2 h 8]
}

Example 3

The next example shows how to define another shape, called SNOWFLAKE which calls the BRANCH shape 9 times while rotating it by 40.

startshape SNOWFLAKE

shape SNOWFLAKE
{
  loop 9 [r (360/9)] BRANCH []
}

shape BRANCH
{
  TRIANGLE [h 160 b 0.8 sat 1]
  BRANCH [s 0.9 y -0.2 a -0.2 h 8]
}

Bonus example

This was my course project for the Grammars for Generative Art course. This 565x565 image contains 39 942 shapes, using only circles. The code can be found in my context-free-artwork repository.

Even more

The examples above show only a fraction of what you can achieve with Context Free. More detailed information about these and other features can be found in the Wiki page. You can also check the official Context Free Gallery for many stunning images.

Generative music

Music combined with live coding is another popular form of generative art but, unfortunately, I haven’t experimented with it yet. Here are some amazing examples: