中式八球：白球撞出来的那条线

fx-billiard

local Billiard = {}
local KEY = { STEP = 0.008, FRICTION = 1.1, R = 10 }
local balls = {}

local function SplitMove(b, dt)
    -- 按最大步长切割位移，杜绝高速穿透
    local sp = math.sqrt(b.vx * b.vx + b.vy * b.vy)
    local n = math.ceil(sp * dt / KEY.STEP)
    n = math.max(1, math.min(8, n))
    for i = 1, n do
        b.x = b.x + b.vx * dt / n
        b.y = b.y + b.vy * dt / n
        Billiard.CheckWall(b)
        Billiard.CheckPocket(b)
    end
end

function Billiard.Sim(dt)
    local moving = false
    for _, b in ipairs(balls) do
        if b.vx ~= 0 or b.vy ~= 0 then
            SplitMove(b, dt)
            b.vx = b.vx * (1 - dt * KEY.FRICTION)
            b.vy = b.vy * (1 - dt * KEY.FRICTION)
            if math.abs(b.vx) < 4 and math.abs(b.vy) < 4 then
                b.vx, b.vy = 0, 0
            else
                moving = true
            end
        end
    end
    Billiard.Collide()
    if not moving then
        SL:SendEvent("balls_settled")   -- 全停后通知瞄准模块
    end
end

function Billiard.Collide()
    for i = 1, #balls do
        for j = i + 1, #balls do
            local a, b = balls[i], balls[j]
            local dx, dy = b.x - a.x, b.y - a.y
            local d2 = dx * dx + dy * dy
            if d2 < (KEY.R * 2) * (KEY.R * 2) and d2 > 0.01 then
                local d = math.sqrt(d2)
                local nx, ny = dx / d, dy / d
                -- 沿法线交换分离速度
                local rel = (a.vx - b.vx) * nx + (a.vy - b.vy) * ny
                if rel > 0 then
                    a.vx = a.vx - rel * nx
                    a.vy = a.vy - rel * ny
                    b.vx = b.vx + rel * nx
                    b.vy = b.vy + rel * ny
                    SL:PlayFxAt("hit_spark", (a.x + b.x) / 2, (a.y + b.y) / 2)
                end
            end
        end
    end
end

return Billiard