Array of characters to use for rendering, ordered from lowest to highest intensity
density of rain drops (0-1). Higher values create more rain streams.
minimum length of rain drops in characters.
maximum length of rain drops in characters.
minimum falling speed multiplier for rain drops.
maximum falling speed multiplier for rain drops.
probability of character mutation per frame (0-1).
background fade opacity for trail effect (0-1).
Options for configuring a rain pattern.