How to do trilinear interpolation?

[x86_architecture (TritiumAndDeuterium)]

Hello there. I’ve been working on something that needs trilinear interpolation, and here is my current function

Trilinear Interpolation - Roblox

I based it on this answer on stackoverflow.

Trilinear interpolation

And this.

The issue is it’s supposed to interpolate where one corner is one, and all other corners are 0 however, this doesn’t seem to do that. (I’m interpolating part transparencies for the sake of making sure it works)

In the screenshot, notice how one corner is supposed to be one, and all other corners are supposed to be 0

It might be hard to see, but in the second screenshot, notice how 2 corners are transparent instead of one. Is there any way I can fix this?

Here is the code, for those of you who don’t want to get the model

function interpolate(x,y,alpha) --simple linear interpolation
	local difference=y-x
	local progress=alpha*difference
	local result=progress+x
	return result
end

function getBilinearValue(value00,value10,value01,value11,xProgress,yProgress)
	local top=interpolate(value00,value10,xProgress) --get progress across line A
	local bottom=interpolate(value01,value11,yProgress) --get line B progress
	local middle=interpolate(top,bottom,yProgress) --get progress of line going
	return middle                              --between point A and point B
end

function getTriValue(v1, v2, v3, v4, v5, v6, v7, v8, x, y, z)
	local top = getBilinearValue(v1, v2, v3, v4, x, y)
	local bottom = getBilinearValue(v5, v6, v7, v8, x, y)
	local middle = interpolate(top, bottom, z)
	return middle
end

for x = 1, 16 do
	wait()
	for y = 1, 16 do
		for z = 1, 16 do
			local value = getTriValue(0, 0, 0, 1, 0, 0, 0, 0, x / 16, y / 16, z / 16)
			local block = Instance.new("Part")
			block.Anchored = true
			block.Size = Vector3.new(2, 2, 2)
			block.CFrame = CFrame.new(x * 2, y * 2, z * 2)
			block.Parent = workspace
			block.Transparency = value
		end
	end
end

Is there any way I can fix this issue?

[DrKittyWaffles]

@x86_architecture

local bottom=interpolate(value01,value11,yProgress)

This should say:

local bottom=interpolate(value01,value11,xProgress)

here is my own code for doing this which i think looks much nicer than your scrap pile.

local function linear(x, y, a)
	return (1 - a) * x + a * y
end

local function bilinear(x, y, j, k, a, b)
	return linear(linear(x, y, a), linear(j, k, a), b)
end

local function trilinear(x, y, j, k, l, m, n, o, a, b, c)
	return linear(bilinear(x, y, j, k, a, b), bilinear(l, m, n, o, a, b), c)
end

for x = 1, 16 do
	for y = 1, 16 do
		for z = 1, 16 do
			local w = trilinear(0, 0, 0, 1, 0, 0, 0, 0, x / 16, y / 16, z / 16)
			local p = Instance.new("Part")
			
			p.Anchored = true
			p.Size = Vector3.new(2, 2, 2)
			p.CFrame = CFrame.new(x * 2, y * 2, z * 2)
			p.Transparency = w
			p.Parent = workspace
		end
	end
end