2D physics

Suggestions
1

Was just poking Love2D, and noticed it has a 2D physics engine.

Just sayin.

So, while it would be keen to have one built-in (add it to the ever-growing list), I’m wondering just how nasty a Box2D translation to lua would be (like they did for javascript). Hmmm… I may have something to do after my current project (still working on vector fonts - nutty, I know).

2

Hi there, I’m the physics guy at Two Lives Left (see Crabitron). I’ve started integrating Box2D into Codea and it works pretty well. At the moment I’ve only got circle’s and no contact events. Here’s the example I’m working with at the moment.


    body = nil
    ground = nil
    -- Use this function to perform your initial setup
    function setup()
        print("Hello Physics World!")
        body = circleBody(WIDTH * 0.5,WIDTH * 0.5,100)
        body.restitution = 0.9
        body.radius = 50
        ground = circleBody(WIDTH * 0.5 + 5, 100, 100)
        ground.type = STATIC
    end

    -- This function gets called once every frame
    function draw()
        -- This sets the background color to black
        background(0, 0, 0)
        noFill()
        strokeWidth(5)
        if body then
            stroke(255, 0, 0, 255)
            pushMatrix()
            translate(body.x, body.y)
            rotate(body.angle)
            line(0, 0, body.radius, 0)
            ellipse(0, 0, body.radius * 2, body.radius * 2)
            popMatrix()
        
            if CurrentTouch.state == BEGAN then
                body.y = body.y + 100
            end
        
            if body.y < 0 then
                body = nil
            end
        end
    
        stroke(255, 183, 0, 255)
        ellipse(ground.x, ground.y, ground.radius * 2, ground.radius * 2)
    end

You basically just create a circleBody with a position and radius. You can then set any other property. We are also looking at having polygonBody as well, which will have an inline editor for editing the vertices, as well as automatic convex decomposition. We will also probably have a compositeBody, which can combine several basic shape bodies.

Let me know what you think.

3

I think that’s totally cool, is what I think. I never messed with Box2D past the circles/rectangles stuff - no links or chains or joints or such - so what you describe would keep me busy for a while. It sounds very much like you’re on the right track.

4

I hope the b2world object ref will be accessible so that we could set its gravity interactively.