Basic Celestial Simulation

-- Initialize physics
local physics = require("physics")
physics.start()
physics.setGravity(0, 0) -- Set gravity to 0

-- Core Variables
screenW = display.contentWidth
screenH = display.contentHeight

-- Table to keep track of spheres
local spheres = {}

-- Function to create a new sphere
local function createSphere(x, y, radius, mass)
    local sphere = display.newCircle(x, y, radius)
    physics.addBody(sphere, {radius=radius, density=mass/(math.pi*radius*radius), bounce=0.25})
    sphere.mass = mass
    table.insert(spheres, sphere)
    return sphere
end

-- Function to update gravitational forces
local function updateGravity()
    for i = 1, #spheres do
        for j = i+1, #spheres do
            local sphere1 = spheres[i]
            local sphere2 = spheres[j]
            local dx = sphere2.x - sphere1.x
            local dy = sphere2.y - sphere1.y
            local distance = math.sqrt(dx*dx + dy*dy)
            local force = (sphere1.mass * sphere2.mass) / (distance * distance)
            local forceX = force * (dx / distance)
            local forceY = force * (dy / distance)

            sphere1:applyForce(forceX, forceY, sphere1.x, sphere1.y)
            sphere2:applyForce(-forceX, -forceY, sphere2.x, sphere2.y)
        end
    end
end

-- Create screen boundaries that fit any screen size
local function createWalls()
    local leftWall = display.newRect(display.screenOriginX, display.contentCenterY, 1, display.actualContentHeight)
    local rightWall = display.newRect(display.actualContentWidth + display.screenOriginX, display.contentCenterY, 1, display.actualContentHeight)
    local topWall = display.newRect(display.contentCenterX, display.screenOriginY, display.actualContentWidth, 1)
    local bottomWall = display.newRect(display.contentCenterX, display.actualContentHeight + display.screenOriginY, display.actualContentWidth, 1)

    physics.addBody(leftWall, "static")
    physics.addBody(rightWall, "static")
    physics.addBody(topWall, "static")
    physics.addBody(bottomWall, "static")
end

-- Function to create a new sphere
local function createSphere(x, y, radius, mass)
    local sphere = display.newCircle(x, y, radius)
    physics.addBody(sphere, {radius=radius, density=mass/(math.pi*radius*radius), bounce=0.25})
    sphere.mass = mass
    table.insert(spheres, sphere)

    -- Make spheres draggable
    function sphere:touch(event)
        if event.phase == "began" then
            display.getCurrentStage():setFocus(self, event.id)
            self.isFocus = true
            self.markX = self.x
            self.markY = self.y
        elseif self.isFocus then
            if event.phase == "moved" then
                self.x = event.x - event.xStart + self.markX
                self.y = event.y - event.yStart + self.markY
            elseif event.phase == "ended" or event.phase == "cancelled" then
                display.getCurrentStage():setFocus(self, nil)
                self.isFocus = false
            end
        end
        return true
    end

    sphere:addEventListener("touch", sphere)
    return sphere
end


-- Create some spheres
createSphere(160, 240, 20, 500) -- x, y, radius, mass
createSphere(320, 240, 15, 1)

-- Create walls
createWalls()

-- Update gravity every frame
Runtime:addEventListener("enterFrame", updateGravity)