sparks: Spark functions to control tree growth
In flametree: Generate Random Tree-Like Images

Description Usage Arguments Details Value Examples

Spark functions to control tree growth

spark_linear(x = 0, y = 0, tree = 0, time = 0, constant = 0)

spark_decay(x = 0, y = 0, tree = 0, time = 0, multiplier = 2, constant = 0)

spark_random(multiplier = 3, constant = 0)

spark_nothing()

`x`	Weight given to the horizontal co-ordinate
`y`	Weight given to the horizontal co-ordinate
`tree`	Weight given to the tree number
`time`	Weight given to the time point
`constant`	Constant value to be added to the output
`multiplier`	Scaling parameter that multiplies the output

Some arguments to flametree_grow() take numeric input, but seg_col, seg_wid, shift_x, and shift_y all take functions as their input, and are used to control how the colours (seg_col) and width (seg_wid) of the segments are created, as well as the horizontal (shift_x) and vertical (shift_y) displacement of the trees are generated. Functions passed to these arguments take four inputs: coord_x, coord_y, id_tree, and id_time as input. Any function that takes these variables as input and produces a numeric vector of the same length as the input can be used for this purpose. However, as a convenience, four "spark" functions are provided that can be used to create functions that are suitable for this purpose: spark_linear(), spark_decay(), spark_random(), and spark_nothing(). Arguments passed to one of the spark functions determine the specific function is generated. For example, spark_linear() can be used to construct any linear combination of the inputs: spark_linear(x = 3, y = 2) would return a function that computes the sum (3 * coord_x) + (2 * coord_y). Different values provided as input produce different linear functions. Analogously, spark_decay() returns functions that are exponentially decaying functions of a linear combination of inputs. The spark_random() generator can be used to generate functions that return random values, and spark_nothing() produces a function that always returns zero regardless of input.

A function that takes coord_x, coord_y, id_tree, and id_time as input, and returns a numeric vector as output.

# returns a linear function of x and y
spark_linear(x = 3,  y = 2)

# returns a function of time that decays
# exponentially to an asymptote
spark_decay(time = .1, constant = .1)

# returns a numeric vector containing
# copies of the same uniform random number
# constrained to lie between -2.5 and 2.5
spark_random(multiplier = 5)

# returns a function that always produces
# a vector of zeros
spark_nothing()