混沌火种：火球要打头不打脚

fx-chaotic

local CONST = {
    SPEED          = 560,      -- 飞行速度
    AIM_HEIGHT     = 64,       -- 瞄点高度: 头胸
    BURN_RADIUS    = 112,      -- 爆燃半径
    BURN_SEGMENTS  = 40,       -- 法阵分段
    BURN_DURATION  = 1.8,      -- 驻留
    BURN_TICK      = 0.45,     -- 灼烧间隔
}

function chaoticSeed:Launch(caster, target)
    self._ball = {
        x = caster:GetX() + caster:GetFaceSign() * 26,
        y = caster:GetY() - 52,
        target = target
    }
end

function chaoticSeed:UpdateBall(dt)
    local b = self._ball
    if not b then return end
    local tx = b.target:GetX()
    local ty = b.target:GetY() - CONST.AIM_HEIGHT       -- 每帧重瞄头胸
    local dx, dy = tx - b.x, ty - b.y
    local dist = math.sqrt(dx * dx + dy * dy)
    local step = CONST.SPEED * dt
    if dist <= step then
        self:Explode(tx, ty)
        self._ball = nil
    else
        b.x, b.y = b.x + dx / dist * step, b.y + dy / dist * step
    end
end