【网络通信】碰撞检测：圆形碰撞的粗筛与精判

---粗筛：距离平方比较，免开方
local function broadPhase(ax, ay, bx, by, range)
    local dx = ax - bx
    local dy = ay - by
    return dx * dx + dy * dy <= range * range
end

---精判：技能扇形的角度校验
local function narrowPhase(actor, tx, ty, face, arc)
    local dx = tx - actor.x
    local dy = ty - actor.y
    local ang = math.deg(math.atan2(dy, dx))
    local diff = math.abs((ang - face + 180) % 360 - 180)
    return diff <= arc / 2
end

---烈火剑法的判定：2 格扇形 90 度
function Combat.fireSwordHit(actor, target)
    if not broadPhase(actor.x, actor.y, target.x, target.y, 2) then
        return false
    end
    return narrowPhase(actor, target.x, target.y,
        actor:GetFacing(), 90)
end

---群体技能的批量判定：先桶后筛
function Combat.aoeHit(actor, cx, cy, radius, arc)
    local hits = {}
    local candidates = Grid.queryCircle(cx, cy, radius)
    for _, t in ipairs(candidates) do
        if broadPhase(cx, cy, t.x, t.y, radius)
            and narrowPhase(actor, t.x, t.y,
                actor:GetFacing(), arc) then
            hits[#hits + 1] = t
            if #hits >= 12 then break end   -- 单次上限
        end
    end
    return hits
end