ff_api_perlin_noise_comparison.lua

function prepare()
	--	constants
	AMPLITUDE_CORRECTION_FACTOR = 1.731628995	
	ROUGHNESS_THRESHOLD = 0.00001
	REMAINDER_THRESHOLD = 0.00001

	aspect = OUTPUT_HEIGHT / OUTPUT_WIDTH * 2

	--	input values
	local details = get_slider_input(DETAILS) * 10 + 1
	OCTAVES_COUNT = math.floor(details)
	NOISE_SIZE = get_slider_input(SCALE)
	local remainder = details - OCTAVES_COUNT
	if (remainder > REMAINDER_THRESHOLD) then
		OCTAVES_COUNT = OCTAVES_COUNT + 1
	end
		
	-- noise generation
	local roughness = ROUGHNESS_THRESHOLD + 	
		get_slider_input(ROUGHNESS) * (1.0 - ROUGHNESS_THRESHOLD)	
		
	OCTAVES = {}	
	local cell_size = (0.01 + NOISE_SIZE * 0.99) * 150	
	local scale = roughness	
	local octave_index	
	for octave_index = 1, OCTAVES_COUNT do	
		if (scale < ROUGHNESS_THRESHOLD) then	
			OCTAVES_COUNT = octave_index - 1	
			break	
		end	
		OCTAVES[octave_index] = {cell_size, scale}	
		cell_size = cell_size * 0.5	
		scale = scale * roughness	
	end	
		
	if (remainder >= 0.001) then	
		OCTAVES[OCTAVES_COUNT][2] = OCTAVES[OCTAVES_COUNT][2] * remainder	
	end	
	
	NORM_FACTOR = 0	
	for octave_index = 1, OCTAVES_COUNT do	
		NORM_FACTOR = NORM_FACTOR + OCTAVES[octave_index][2] ^ 2	
	end
	NORM_FACTOR = 1 / math.sqrt(NORM_FACTOR)	
	
	set_perlin_noise_seed(get_intslider_input(NOISE_VARIATION))	
end;
	
function get_sample(x, y)	
	local r, g, b, a = get_sample_map(x, y, BACKGROUND)	
	local noise_r, noise_g, noise_b, noise_a = get_sample_map(x, y, NOISE)	
	
	local alpha = 0	
	local octave_index 	
	for octave_index = 1, OCTAVES_COUNT do	
		local size = OCTAVES[octave_index][1]	
		local opacity = OCTAVES[octave_index][2]	
		local noise_z = octave_index	
		alpha = alpha + opacity * (2*get_perlin_noise(x, y, noise_z, size) - 1)	
	end	
		
	alpha = (alpha * NORM_FACTOR + AMPLITUDE_CORRECTION_FACTOR) * 	
		(0.5 / AMPLITUDE_CORRECTION_FACTOR)	
		
	return blend_normal(r, g, b, a, noise_r, noise_g, noise_b, noise_a, alpha)	
end;