Example of implementing 3D touch. In progress.

3D touch.lua

--# Main
function setup()
    displayMode(FULLSCREEN)
    sky = Skybox()
    forward, right, up = vec3(0,0,-1), vec3(1,0,0), vec3(0,1,0)
    rays = {}
    
    -- creating some random triangles to hit
    tris = {}
    local r = function (d) return math.random(-d,d) end
    for i=1,300 do
        local m = mesh()
        local r1 = vec3(r(2000),r(2000),r(2000))
        local r2 = r1 + vec3(r(100),r(100),r(100))
        local r3 = r1 + vec3(r(100),r(100),r(100))
        m.vertices = {r1,r2,r3}
        m:setColors(color(229, 215, 33, 255))
        tris[i] = m 
    end
end

function draw()
    background(0, 0, 0, 255)
    perspective(45, WIDTH/HEIGHT, .1, 50000)

    -- rotate camera with iPad orientation
    local m = matrix()
        :rotate(RotationRate.z, forward.x,forward.y,forward.z)
        :rotate(-RotationRate.x, right.x,right.y,right.z)
        :rotate(-RotationRate.y, up.x,up.y,up.z)
    forward, right, up = mult(m,forward),mult(m,right),mult(m,up)

    camera(0,0,0, forward.x, forward.y, forward.z, up.x, up.y, up.z)

    for i,o in ipairs(rays) do
        pushMatrix()
        local p = o.dir * o.t

        translate(p.x,p.y,p.z)
        o.m:draw()
        popMatrix()
        -- remove mesh when tween is finished
        if o.t == 2000 then table.remove(rays, i) end
    end
    for i,o in ipairs(tris) do
        o:draw()
    end
    
    rotate(-90,1,0,0)
    sky:draw()
end

function touched(touch)
    if touch.state == BEGAN then
        local o = addRay(touch)

        -- check if a triangle is hit
        local d,j = false
        for i,tri in ipairs(tris) do
            local vs = tri.vertices
            d = trintersect(vec3(0,0,0), o.dir, vs[1], vs[2], vs[3])
            if d then j=i;break end
        end
        if not d then
            tween(.8, o, {t=2000})
        else -- if hit move to distance d then remove triangle
            tween(.8, o, {t=d}, tween.easing.quadInOut, function ()
                table.remove(tris,j)
                o.t = 2000
            end)            
        end
    end
end

function addRay(touch)
    -- touch position in interval -1,1
    local tp = vec2(touch.x/WIDTH-.5,touch.y/HEIGHT-.5) * 2
    -- distance from eye to screen for perspective(45)
    local d = 1/math.tan(math.rad(45/2))

    local p = vec3(0,0,0)    
    local dir = forward*d + up*tp.y + right*tp.x*WIDTH/HEIGHT

    local o = {
        t = 100,
        dir = dir:normalize(),
        m = Mesh("Space Art:Red Explosion"):right(right)
            :up(up):quad(p, 10,10)
    }
    table.insert(rays, o)
    return o
end





--# Mesh
Mesh = class()

function Mesh:init(texture)
    self.vs, self.uvs = {}, {}
    self.buffers = {}
    self.texture = texture
    self.ds = {
        right = vec3(1,0,0),
        up = vec3(0,1,0),
        size = vec2(1,1),
        center = true
    }
    self:reset()
end

function Mesh:reset()
    self.ps = {}
    for k,v in pairs(self.ds) do
        self.ps[k] = v
    end
    return self
end
function Mesh:defaults()
    for k,v in pairs(self.ps) do
        self.ds[k] = v
    end
    return self
end

function Mesh:buffer(name, val, n)
    if not self.buffers[name] then
        self.buffers[name] = {}
    end
    for i=1,n do
        table.insert(self.buffers[name], val)
    end
    return self
end

function Mesh:right(v) self.ps.right = v;return self end
function Mesh:up(v) self.ps.up = v;return self end
function Mesh:size(v) self.ps.size = v;return self end
function Mesh:rotate(a) self.ps.rotate = a;return self end

function mult(m, v) -- matrix multiplication
    return vec3(
        m[1]*v.x+m[2]*v.y+m[3]*v.z,
        m[5]*v.x+m[6]*v.y+m[7]*v.z,
        m[9]*v.x+m[10]*v.y+m[11]*v.z
    )
end
function Mesh:quad(pos, w, h)
    local ps = self.ps
    w,h = w or ps.size.x, h or w or ps.size.y
    local right = ps.right * w
    local up = ps.up * h
    if ps.rotate then
        local n = right:cross(up):normalize()
        local m = matrix():rotate(ps.rotate, n.x,n.y,n.z)
        right, up = mult(m,right), mult(m,up)
    end
    if ps.center then
        pos = pos - (right+up)*.5
    end

    table.insert(self.vs, pos)
    table.insert(self.vs, pos+right)
    table.insert(self.vs, pos+up)
    table.insert(self.vs, pos+right)
    table.insert(self.vs, pos+up+right)
    table.insert(self.vs, pos+up)
    
    table.insert(self.uvs, vec2(0,0))
    table.insert(self.uvs, vec2(1,0))
    table.insert(self.uvs, vec2(0,1))
    table.insert(self.uvs, vec2(1,0))
    table.insert(self.uvs, vec2(1,1))
    table.insert(self.uvs, vec2(0,1))
    self:reset()
    return self
end

function Mesh:construct(s)
    local m = mesh()
    if s then m.shader = s end
    m.vertices, m.texCoords = self.vs, self.uvs
    if self.texture then
        m.texture = asset(self.texture)
    end
    for k,v in pairs(self.buffers) do
          (m:buffer(k)):set(v)
    end
    m:setColors(color(255, 255, 255, 255))
    self.m = m
    return m
end


function Mesh:draw()
    if not self.m then self:construct() end
    self.m:draw()
end

-- http://en.wikipedia.org/wiki/Möller–Trumbore_intersection_algorithm
function trintersect(origin, dir, v1, v2, v3)
    local epsilon = .001
    local e1, e2 = v2-v1, v3-v1
    local pv = dir:cross(e2)
    local det = e1:dot(pv)
    if det > -epsilon and det < epsilon then return false end
    local invDet = 1/det
    local tv = origin - v1
    local u = tv:dot(pv) * invDet
    if (u < 0) or (u > 1) then return false end
    local qv = tv:cross(e1)
    local v = dir:dot(qv) * invDet
    if v < 0 or (u+v) > 1 then return false end
    local hitDistance = e2:dot(qv) * invDet
    return (hitDistance >= 0) and hitDistance or false
end

--# Skybox
Skybox = class()

function Skybox:init()
    local s = 20000
    local hs = s/2
    self.ms = {
        Mesh("GSSkyny"):quad(vec3(0,0,-hs),s):construct(),
        Mesh("GSSkypy"):up(vec3(0,-1,0)):
        quad(vec3(0,0,hs),s):construct(), 

        Mesh("GSSkynz"):right(vec3(-1,0,0)):
        up(vec3(0,0,1)):quad(vec3(0,-hs,0),s):construct(),
        Mesh("GSSkypz"):up(vec3(0,0,1)):
        quad(vec3(0,hs,0),s):construct(),
 
        Mesh("GSSkypx"):right(vec3(0,-1,0)):up(vec3(0,0,1)):
        quad(vec3(hs,0,0),s):construct(),
        Mesh("GSSkynx"):right(vec3(0,1,0)):up(vec3(0,0,1)):
        quad(vec3(-hs,0,0),s):construct()       
    }
end

function Skybox:draw()
    for i,v in ipairs(self.ms) do
        v:draw()
    end
end

function Skybox:touched(touch)
end

function Skybox:hit(origin, ray)
    local vs = self.ms[1].vertices
    if trintersect(origin, ray, vs[1],vs[2],vs[3]) or
       trintersect(origin, ray, vs[4],vs[5],vs[6]) then
        print("yes")
    end
end
--# Assets
-- utility function to download assets for the first run.
-- returns an empty image with the correct size while waiting
-- for http.request result.
local baseUrl = "http://goingsouth.meteor.com/"
local c = ContentScaleFactor
local imageMap = {
    GSWing = {256,256,"wing.png"},
    GSTail = {64,256,"tailfeather.png"},
    GSTnlogy = {512,256,"tnlogy.png"},
    GSLogo = {512,256,"goingsouth.png"},
    GSClouds = {256,256, "clouds.png"},
    -- Using skybox graphics by Jochum Skoglund
    GSSkynx = {c*512,c*512,"skybox/nx.jpg"},
    GSSkyny = {c*512,c*512,"skybox/ny.jpg"},
    GSSkynz = {c*512,c*512,"skybox/nz.jpg"},
    GSSkypx = {c*512,c*512,"skybox/px.jpg"},
    GSSkypy = {c*512,c*512,"skybox/py.jpg"},
    GSSkypz = {c*512,c*512,"skybox/pz.jpg"},  
}
function asset(name)
    if string.find(name, ":") then return name end
    local img = readImage("Documents:" .. name)
    if img == nil then
        local w,h,url = unpack(imageMap[name] or {1,1})
        img = image(w,h)
        if url then
            http.request(baseUrl .. url, function (data)
                pushStyle()
                setContext(img)
                spriteMode(CORNER)
                sprite(data,0,0,w,h)
                setContext()
                popStyle()
                saveImage("Documents:" .. name, data)
            end)
        end
    end
    return img
end