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https://github.com/sbrl/Minetest-WorldEditAdditions.git
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52 lines
1.7 KiB
Lua
52 lines
1.7 KiB
Lua
-- Ported from Javascript by Starbeamrainbowlabs
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-- Original source: https://github.com/sidorares/gaussian-convolution-kernel/
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-- From
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-- the code is taken from https://github.com/mattlockyer/iat455/blob/6493c882f1956703133c1bffa1d7ee9a83741cbe/assignment1/assignment/effects/blur-effect-dyn.js
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-- (c) Matt Lockyer, https://github.com/mattlockyer
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-- hypotenuse has moved to utils/numbers.lua
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--[[
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* Generates a kernel used for the gaussian blur effect.
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*
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* @param dimension is an odd integer
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* @param sigma is the standard deviation used for our gaussian function.
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*
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* @returns an array with dimension^2 number of numbers, all less than or equal
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* to 1. Represents our gaussian blur kernel.
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]]--
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function worldeditadditions.conv.kernel_gaussian(dimension, sigma)
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if not (dimension % 2) or math.floor(dimension) ~= dimension or dimension < 3 then
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return false, "The dimension must be an odd integer greater than or equal to 3"
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end
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local kernel = {};
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local two_sigma_square = 2 * sigma * sigma;
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local centre = (dimension - 1) / 2;
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local sum = 0
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for i = 0, dimension-1 do
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for j = 0, dimension-1 do
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local distance = worldeditadditions.hypotenuse(i, j, centre, centre)
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-- The following is an algorithm that came from the gaussian blur
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-- wikipedia page [1].
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--
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-- http://en.wikipedia.org/w/index.php?title=Gaussian_blur&oldid=608793634#Mechanics
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local gaussian = (1 / math.sqrt(
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math.pi * two_sigma_square
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)) * math.exp((-1) * ((distance ^ 2) / two_sigma_square));
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sum = sum + gaussian
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kernel[i*dimension + j] = gaussian
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end
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end
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-- Returns the unit vector of the kernel array.
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for k,v in pairs(kernel) do
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kernel[k] = kernel[k] / sum
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end
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return true, kernel
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end
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