okshift.lua

-- OKShift for Aseprite

-- OKLab L is perceptual lightness, so rotating hue in OKLCh keeps perceptual brightness.
-- way more swag than HSV/HSL/YIQ.

-- color math

local function srgb_to_linear(c)
	if c<=0.04045 then return c/12.92 end
	return ((c+0.055)/1.055)^2.4
end

local function linear_to_srgb(c)
	if c<=0.0031308 then return c*12.92 end
	return 1.055*(c^(1/2.4))-0.055
end

-- stands for cube root
local function cbrt(x)
	-- lua's ^ doesn't like negative bases with fractional exponents, gives NaNs for some reason
	if x<0 then return -((-x)^(1/3)) end
	return x^(1/3)
end

local function rgb_to_oklab(r,g,b)
	r = srgb_to_linear(r/255)
	g = srgb_to_linear(g/255)
	b = srgb_to_linear(b/255)

	local l = 0.4122214708*r+0.5363325363*g+0.0514459929*b
	local m = 0.2119034982*r+0.6806995451*g+0.1073969566*b
	local s = 0.0883024619*r+0.2817188376*g+0.6299787005*b

	local l_ = cbrt(l)
	local m_ = cbrt(m)
	local s_ = cbrt(s)

	local L = 0.2104542553*l_+0.7936177850*m_-0.0040720468*s_
	local a = 1.9779984951*l_-2.4285922050*m_+0.4505937099*s_
	local bb = 0.0259040371*l_+0.7827717662*m_-0.8086757660*s_
	return L,a,bb
end

local function oklab_to_rgb(L,a,b)
	local l_ = L+0.3963377774*a+0.2158037573*b
	local m_ = L-0.1055613458*a-0.0638541728*b
	local s_ = L-0.0894841775*a-1.2914855480*b

	local l = l_*l_*l_
	local m = m_*m_*m_
	local s = s_*s_*s_

	local r = 4.0767416621*l-3.3077115913*m+0.2309699292*s
	local g = -1.2684380046*l+2.6097574011*m-0.3413193965*s
	local bl = -0.0041960863*l-0.7034186147*m+1.7076147010*s

	r = linear_to_srgb(r)
	g = linear_to_srgb(g)
	bl = linear_to_srgb(bl)

	-- gamut clip
	r = math.max(0,math.min(1,r))
	g = math.max(0,math.min(1,g))
	bl = math.max(0,math.min(1,bl))

	return math.floor(r*255+0.5),math.floor(g*255+0.5),math.floor(bl*255+0.5)
end

local function shift_color(r,g,b,hueDeg,chromaMult,lightShift)
	local L,a,bb = rgb_to_oklab(r,g,b)

	-- to OKLCh polar form
	local C = math.sqrt(a*a+bb*bb)
	local h = math.atan(bb,a)

	h = h+math.rad(hueDeg)
	C = C*chromaMult
	L = L+lightShift

	a = C*math.cos(h)
	bb = C*math.sin(h)

	return oklab_to_rgb(L,a,bb)
end

-- main

-- memorise packed rgba values
local function make_shifter(hue,chroma,light)
	local pc = app.pixelColor
	local cache = {}

	return function(px)
		local out = cache[px]
		if out==nil then
			local a = pc.rgbaA(px)
			if a==0 then
				out = px
			else
				local nr,ng,nb = shift_color(pc.rgbaR(px),pc.rgbaG(px),pc.rgbaB(px),hue,chroma,light)
				out = pc.rgba(nr,ng,nb,a)
			end
			cache[px] = out
		end
		return out
	end
end

-- indexed sprites... repoint every pixel at the closest color the palette already has
-- same as native hue/sat. closest is measured in OKLab, obviously :3

local function palette_candidates(palette,transparentIdx)
	local cand = {}
	for i=0,#palette-1 do
		local c = palette:getColor(i)
		-- an invisible entry is never a good place to land
		if i~=transparentIdx and c.alpha>0 then
			local L,a,b = rgb_to_oklab(c.red,c.green,c.blue)
			cand[#cand+1] = {idx=i,L=L,a=a,b=b,alpha=c.alpha}
		end
	end
	return cand
end

local function nearest_index(cand,r,g,b,alpha,fallback)
	local L,a,bb = rgb_to_oklab(r,g,b)
	local best,bestD = fallback,nil
	for k=1,#cand do
		local c = cand[k]
		local dL,da,db = L-c.L,a-c.a,bb-c.b
		-- keep a semi-transparent entry from stealing an opaque pixel
		local dA = (alpha-c.alpha)/255
		local d = dL*dL+da*da+db*db+dA*dA
		if bestD==nil or d<bestD then
			bestD,best = d,c.idx
		end
	end
	return best
end

-- memorise index->index
local function make_index_shifter(palette,transparentIdx,hue,chroma,light)
	local cand = palette_candidates(palette,transparentIdx)
	local n = #palette
	local cache = {}

	return function(px)
		local out = cache[px]
		if out==nil then
			out = px
			-- px>=n means the image points outside its own palette, leave it alone
			if px~=transparentIdx and px<n then
				local c = palette:getColor(px)
				if c.alpha>0 then
					local nr,ng,nb = shift_color(c.red,c.green,c.blue,hue,chroma,light)
					out = nearest_index(cand,nr,ng,nb,c.alpha,px)
				end
			end
			cache[px] = out
		end
		return out
	end
end

local function process_image(image,celPos,sel,shift)
	local x0,y0,x1,y1 = 0,0,image.width,image.height

	-- clip to the selection bounding box
	if sel then
		local b = sel.bounds
		x0 = math.max(x0,b.x-celPos.x)
		y0 = math.max(y0,b.y-celPos.y)
		x1 = math.min(x1,b.x+b.width-celPos.x)
		y1 = math.min(y1,b.y+b.height-celPos.y)
		-- selection misses this cel entirely
		if x1<=x0 or y1<=y0 then return end
	end

	for it in image:pixels(Rectangle(x0,y0,x1-x0,y1-y0)) do
		if not sel or sel:contains(it.x+celPos.x,it.y+celPos.y) then
			local px = it()
			local out = shift(px)
			-- skip transparent pipsis
			if out~=px then it(out) end
		end
	end
end

local function is_identity(hue,chroma,light)
	return hue==0 and chroma==1 and light==0
end

local function target_cels(allCels)
	local cels = {}
	if allCels and #app.range.cels>0 then
		for _,c in ipairs(app.range.cels) do
			table.insert(cels,c)
		end
	elseif app.activeCel then
		table.insert(cels,app.activeCel)
	end

	-- tilemap cels hold tile indices, not colors!!!!!
	local out = {}
	for _,c in ipairs(cels) do
		if not c.layer.isTilemap then
			table.insert(out,c)
		end
	end
	return out
end

local function active_selection(sprite,selOnly)
	if selOnly and not sprite.selection.isEmpty then
		return sprite.selection
	end
	return nil
end

-- which palette does a frame paint with? a sprite can carry several, each one owning frames from its own frame onwards.
-- NEVER ipairs() over sprite
local function palette_frames(pals)
	if #pals<2 then return nil end
	local ok,frames = pcall(function()
		local f = {}
		for p=1,#pals do
			local fr = pals[p].frame
			f[p] = fr and fr.frameNumber or 1
		end
		return f
	end)
	if ok then return frames end
	return nil -- old aseprite without Palette.frame, just use the first one
end

-- the palette with the highest start frame at or before this one. ties go to the earlier palette, and it doesn't assume they came in frame order
local function palette_for_frame(frames,frameNumber)
	local p,best = 1,nil
	if frames then
		for i=1,#frames do
			if frames[i]<=frameNumber and (best==nil or frames[i]>best) then
				p,best = i,frames[i]
			end
		end
	end
	return p
end

-- hands out the right shifter for a given cel
local function make_shifter_factory(sprite,hue,chroma,light)
	if sprite.colorMode~=ColorMode.INDEXED then
		local shift = make_shifter(hue,chroma,light)
		return function() return shift end
	end

	local transparentIdx = sprite.transparentColor
	local pals = sprite.palettes
	local frames = palette_frames(pals)
	local byPalette = {}

	return function(cel)
		local p = palette_for_frame(frames,cel.frameNumber)
		local shift = byPalette[p]
		if not shift then
			shift = make_index_shifter(pals[p],transparentIdx,hue,chroma,light)
			byPalette[p] = shift
		end
		return shift
	end
end

-- applyyyy
local function apply_impl(sprite,hue,chroma,light,selOnly,allCels)
	local sel = active_selection(sprite,selOnly)
	local shifterFor = make_shifter_factory(sprite,hue,chroma,light)
	for _,cel in ipairs(target_cels(allCels)) do
		local img = cel.image:clone()
		process_image(img,cel.position,sel,shifterFor(cel))
		cel.image = img
	end
end

-- ui

local function show_dialog(plugin)
	local sprite = app.activeSprite
	if not sprite then
		app.alert("No active sprite!")
		return
	end

	if sprite.colorMode==ColorMode.GRAY then
		app.alert("Grayscale mode has no hue to shift :(")
		return
	end

	-- restore last-used toggles (not sliders!!!!!)
	local prefs = plugin.preferences
	if prefs.selOnly==nil then prefs.selOnly = true end
	if prefs.allCels==nil then prefs.allCels = false end
	if prefs.livePreview==nil then prefs.livePreview = true end

	local dlg

	-- preview. raw byte writes, so the undo stack is skipüped
	local snapCels = nil -- {{cel=cel,bytes=string},...}

	local function clear_preview()
		if snapCels then
			for _,s in ipairs(snapCels) do
				s.cel.image.bytes = s.bytes
			end
			snapCels = nil
		end
	end

	local function do_preview()
		-- always rewind the previous preview first; each preview is fresh from the original
		clear_preview()

		local d = dlg.data
		local hue = d.hue
		local chroma = d.chroma/100
		local light = d.light/100

		if is_identity(hue,chroma,light) then
			app.refresh()
			return
		end

		local sel = active_selection(sprite,d.selOnly)
		local shifterFor = make_shifter_factory(sprite,hue,chroma,light)
		snapCels = {}
		for _,cel in ipairs(target_cels(d.allCels)) do
			table.insert(snapCels,{cel=cel,bytes=cel.image.bytes})
			process_image(cel.image,cel.position,sel,shifterFor(cel))
		end

		app.refresh()
	end

	-- throttle preview fires so it doesn't preview every frame and explodes your shit
	local dirty = false
	local timer
	if Timer then
		timer = Timer{interval=0.05,ontick=function()
			if dirty then
				dirty = false
				do_preview()
			else
				timer:stop()
			end
		end}
	end

	local function on_change()
		if not dlg.data.livePreview then
			dirty = false
			clear_preview()
			app.refresh()
			return
		end

		if not timer then
			do_preview() -- no timer before v1.3
			return
		end

		dirty = true
		if not timer.isRunning then
			timer:start()
		end
	end

	-- dialog ui
	dlg = Dialog{title="OKShift"}
	dlg:slider{id="hue",label="Hue (°)",min=-180,max=180,value=0,onchange=on_change}
	dlg:slider{id="chroma",label="Chroma (%)",min=0,max=200,value=100,onchange=on_change}
	dlg:slider{id="light",label="Lightness ±",min=-50,max=50,value=0,onchange=on_change}
	dlg:separator()
	dlg:check{id="selOnly",label="Selection only",selected=prefs.selOnly,onclick=on_change}
	dlg:check{id="allCels",label="All cels in timeline range",selected=prefs.allCels,onclick=on_change}
	dlg:separator()
	dlg:check{id="livePreview",label="Live preview",selected=prefs.livePreview,onclick=on_change}
	dlg:separator()
	dlg:button{id="ok",text="Apply",focus=true}
	dlg:button{id="cancel",text="Cancel"}

	dlg:show{wait=true}

	if timer then timer:stop() end

	-- the preview never did anything to the undo stack, so clearing it is always ok here
	clear_preview()

	if dlg.data.ok then
		prefs.selOnly = dlg.data.selOnly
		prefs.allCels = dlg.data.allCels
		prefs.livePreview = dlg.data.livePreview

		local hue = dlg.data.hue
		local chroma = dlg.data.chroma/100
		local light = dlg.data.light/100
		if not is_identity(hue,chroma,light) then
			app.transaction("OKShift",function()
				apply_impl(sprite,hue,chroma,light,dlg.data.selOnly,dlg.data.allCels)
			end)
		end
	end

	app.refresh()
end

-- plugin entry

function init(plugin)
	plugin:newCommand{
		id="OKShift",
		title="OKShift",
		group="edit_fx",
		onclick=function()
			show_dialog(plugin)
		end,
		onenabled=function()
			return app.activeSprite~=nil
		end
	}
end

function exit(plugin)
end