疾风残影：跑过的地方留下影子

fx-gale

local AfterImage = {}
local CONST = { KEY = "AfterImage", MAX = 8, FADE = 0.1 }

function AfterImage.Update(dt, actorX, actorY, actorDir, actorFrame)
    AfterImage._acc = (AfterImage._acc or 0) + dt
    if AfterImage._acc < 0.05 then return end          -- 50ms 生成一张
    AfterImage._acc = 0
    table.insert(AfterImage._queue, 1, {
        x = actorX, y = actorY, dir = actorDir,
        frame = actorFrame, a = CONST.FADE * 1.5
    })
    while #AfterImage._queue > CONST.MAX do
        table.remove(AfterImage._queue)
    end
end

function AfterImage.Render()
    for i = #AfterImage._queue, 1, -1 do
        local g = AfterImage._queue[i]
        DrawSprite(g.x, g.y, g.dir, g.frame, g.a * (1 - i / CONST.MAX))
    end
end

return AfterImage