Simple Physics

A very simple physics script. If attached to an object it will have gravity, velocity, angular velocity and land on static voxel data. When it hits something it will always stop moving the object.

You can affect it via setVelocity(velocity, ?angularVelocityDegrees) and setEnabled(bool). You can also change .gravity and .height to affect the physics. The collision body is always a sphere with a diameter of 0.5 by default. Other scripts can add a listener to onHit to do something when it hits the ground.

This is a simple example. Physics will later be handled by the engine.

local self = {}

local enabled = true
self.vel = Vec3()
self.angVel = Vec3()
self.gravity = 20
self.sleeping = false

--everything is handled as a sphere with this diameter
self.height = 0.5


function self:Attach()
    self.component.syncToClients = true

    self.vr = self.object:GetComponentByType("VoxelRenderer")
    local vd = self.object:GetComponentByType("VoxelData")
    self.vd = vd and vd.data

    --fires when hit the ground or other
    ---@class onHit:event
    ---@field addListener fun(script:ScriptInstance, listener:fun())
    self.onHit, self.onHitTrigger = events:makeLocalEvent(self)
end

function self:Update(deltaTime)
    if self.onClient then return end 
    if not enabled then return end
    self:updateSleeping()
    if self.sleeping then return end
    self:updatePhysics()
end

function self:OnActivate()
    --always wake up
    self.sleeping = false
end

---@param velocity Vec3
---@param angularVelocityDegree ?Vec3
function self:setVelocity(velocity, angularVelocityDegrees)
    self.vel = velocity
    self.angVel = angularVelocityDegree or self.angVel
    self.sleeping = false
end

function self:setEnabled(en)
    enabled = en
    --also wake up
    if en then
        self.sleeping = false
    end
end

function self:updatePhysics()
    if self.onClient then
        return
    end

    local tf = self.transform
    local dt = Scene:GetDeltaTime()

    --add gravity 
    self.vel.y = self.vel.y - self.gravity * dt
    
    --update pos, rot
    --quick fix: limit dt to avoid falling through floor on lag
    local dt = math.min(dt, 0.1)
    tf.pos = tf.pos + self.vel * dt
    tf.rot = Quat.Euler(self.angVel * dt) * tf.rot
    
    self:checkCollisionsSimple()
end

--simple raycast down
function self:checkCollisionsSimple()
    if self:getGrounded() then
        local tf = self.transform
        local dist = self:getDistToGround()
        local underground = self.height * 0.5 - dist --dist is 0-0.5
        tf.pos = tf.pos + underground * Vec3.up
        self.sleeping = true
        self.onHitTrigger()
    end
end

function self:updateSleeping()
    if not self.sleeping then return end
    local p = self.transform.pos
    local lp = self.lastPos or Vec3()
    if (p-lp):SqrLength() > 0.1 then
        self.sleeping = false
        self.vel = Vec3()
        self.lastPos = self.transform.pos
    end 
end

function self:getGrounded()
    local grounded = self:getDistToGround() <= self.height * 0.5
    return grounded
end

function self:getDistToGround()
    local pos = self.transform.pos
    local c = Collision()
    c.filter = Filter()
    c.filter.useNotStatic = false
    local hit = c:Raycast(pos, Vec3.down * self.height)[1]
    if not hit then return math.huge end
    local dist = (hit.pos - pos):Len()
    return dist
end

return self