wobble.lua

local function dowobble(cel, data, dataoffset)
    local img = cel.image:clone()
    -- local selection = cel.sprite.selection
    for it in img:pixels() do
        local nx = it.x
        local ny = it.y
        local seed = data.dir == "y" and it.x or it.y
        -- Frequency is number of pixels it takes to perform full phase
        local pos = (seed + dataoffset) / data.frequency
        local offset = math.floor(math.sin(pos * math.pi * 2) * data.amplitude)
        if data.dir == "x" then
            nx = nx + offset
            if data.wrap then
                nx = negmod(nx, img.width)
            else
                nx = math.min(math.max(nx, 0), img.width-1)
            end
        else
            ny = ny + offset
            if data.wrap then
                ny = negmod(ny, img.height)
            else
                ny = math.min(math.max(ny, 0), img.height-1)
            end
        end
        it(cel.image:getPixel(nx, ny))
    end
    cel.image = img
    app.refresh()
end

function negmod(a, b)
    return math.fmod(math.fmod(a, b) + b, b)
end

local cel = app.activeCel
local spr = app.activeSprite
if not cel then return app.alert "No active cel" end

local dlg = Dialog("Wobble")
dlg:number { id="amplitude", label="Amplitude", text="16", focus=true }
    :number { id="frequency", label="Frequency", text="16" }
    :number { id="offset", label="Offset", text="0" }
    :check { id="wrap", label="Wrap", selected=false }
    :check { id="animate", label="Animate", selected=false }
    :combobox { id="dir", label="Direction", option="x", options={ "x", "y" } }
    :button { id="ok", text="OK" }
    :button { text="Cancel" }
dlg:show()

local data = dlg.data
if data.ok then
    app.transaction(
        function()
            if data.animate then
                local cels = app.range.cels
                if not cels then
                    app.alert("No selected cels")
                    return
                elseif #cels <= 1 then
                    app.alert("Need at least two selected cels to animate")
                    return
                end
                for i = 1, #cels do
                    local o = (i - 1) / #cels
                    dowobble(cels[i], data, data.offset + o * data.frequency)
                end
            else
                dowobble(cel, data, data.offset)
            end
        end
    )
end