A Forth Haiku is an attempt to mix mathematics, art, and the Forth programming language. It resembles a texture shader, however, the emphasis is on direct expression in the resulting image.
The Forth program describing each Haiku is run once per pixel over a square image. Forth cells are floating point. Conditions return 1 instead of -1. The position is available from the words x and y, which range from 0 to 1, which the origin in the lower left hand corner. The haiku returns the desired color in (red, green, blue, alpha), with alpha being topmost on the stack. If the stack has less than 4 items default values are assumed: red:0, green:0, blue:0, alpha:1.
Like a traditional haiku, an ideal Forth Haiku has 3 lines of 5, 7, 5 words. Compositions which don't fit the haiku form are either 'short' (less than 140), or 'long'.
Alpha (opacity), can be used to make semi-transparent haiku. Not every haiku will specify alpha (instead relying on the default 1, fully opaque).
Core words (Glossary):
x y t dt mx my button buttons audio @ ! ( \ push pop r@ dup over 2dup drop swap rot -rot = <> < > <= >= and or not min max + - * / mod pow atan2 negate sin cos tan log exp sqrt floor ceil abs pi z+ z* random : if