gistfile1.lua

require("string")

state = {}

function love.load()
  state.size = { cx = love.graphics.getWidth(), cy = love.graphics.getHeight() }
  
  -- ball is a position, a mass, and a velocity
  state.ball = { position = { x = state.size.cx / 2, y = state.size.cy / 2 },
           mass = 50,
           velocity = { x = 0, y = 0 } }
           
  borderColour = { 255, 255, 255, 255 }
  ballColour = { 255, 0, 0, 255 }
end

function love.update(dt)
	-- note that this function doesn't do exactly what it needs to do yet, must be worked out more
	local forces = { {x = 0, y = -9.81 / state.ball.mass} }
	state.ball = ballNext(state.ball, forces, dt)
	
	
	print(string.format("update %f", dt))
	print(string.format("ball: %f, %f", state.ball.position.x, state.ball.position.y))
  
end

function love.draw()
--    love.graphics.print('Hello World!', 400, 300)
  
  -- draw the border
  love.graphics.setColor(borderColour)
  love.graphics.rectangle("line", 0.5, 0.5, state.size.cx, state.size.cy)

  -- draw the ball
  love.graphics.setColor(ballColour)
  love.graphics.circle("fill", state.ball.position.x + 0.5, state.ball.position.y + 0.5, 10)
end

function love.keypressed(key, unicode) 
	if (key == "escape") then
		love.event.push('q')
	end
end

function ballNext(ball, forces, dt)
  -- add new velocities together
  sum = { x = 0, y = 0 }
  
  -- ipairs returns an iterator - for indexed tables
  -- pairs is for key-pair tables
  for _, f in ipairs(forces) do
    sum.x = sum.x + f.x/ball.mass * dt
    sum.y = sum.y + f.y/ball.mass * dt
  end
  
  ball2 = deepcopy(ball)
  ball2.velocity.x = ball2.velocity.x + sum.x
  ball2.velocity.y = ball2.velocity.y + sum.y
  
  ball2.position.x = ball2.position.x + ball2.velocity.x * dt
  ball2.position.y = ball2.position.y + ball2.velocity.y * dt
  
  return ball2
  
end

-- stolen from http://lua-users.org/wiki/CopyTable
function deepcopy(object)
    local lookup_table = {}
    local function _copy(object)
        if type(object) ~= "table" then
            return object
        elseif lookup_table[object] then
            return lookup_table[object]
        end
        local new_table = {}
        lookup_table[object] = new_table
        for index, value in pairs(object) do
            new_table[_copy(index)] = _copy(value)
        end
        return setmetatable(new_table, getmetatable(object))
    end
    return _copy(object)
end