3D screen boundaries

gistfile1.txt

function setup()
    displayMode(FULLSCREEN)
    ScreenFraction=0.7 --reduce the screen size artificially so we can see it works
    perspective()
    camera(0,0,0,0,0,-1)
    xFactor=-1/projectionMatrix()[1]*ScreenFraction
    yFactor=-1/projectionMatrix()[6]*ScreenFraction
    --set up asteroids
    asteroids={}
    for i=1,25 do
        local a={}
        local z=math.random(-1000,-900)
        a.radius=math.random(3,10)
        a.pos=vec3(math.random(-xFactor*z+a.radius,xFactor*z-a.radius),
                   math.random(-yFactor*z+a.radius,yFactor*z-a.radius),
                   z)
        a.velocity=vec3(0,0,2) --moving toward us
        a.colour=color(math.random(0,255),math.random(0,255),math.random(0,255))
        table.insert(asteroids,a)
    end
end

function draw() 
    background(0)
    perspective()
    camera(0,0,0,0,0,-1)
    fill(255)
    local counter=0
    for i,a in pairs(asteroids) do
        counter=counter+1
        pushMatrix()
        translate(a.pos.x,a.pos.y,a.pos.z)
        fill(a.colour)
        ellipse(0,0,a.radius*2)
        popMatrix()
        a.pos=a.pos+a.velocity
        if math.abs(a.pos.x)-a.radius>a.pos.z*xFactor or math.abs(a.pos.y)-a.radius>a.pos.z*yFactor then
            table.remove(asteroids,i)
        end
    end
    --all this below is just to draw a rectangle showing the reduced screen boundary
    ortho()
    viewMatrix(matrix())
    pushStyle()
    noFill()
    stroke(255)
    strokeWidth(2)
    rectMode(CENTER)
    rect(WIDTH/2,HEIGHT/2,WIDTH*ScreenFraction,HEIGHT*ScreenFraction)
    popStyle()
end