introduction

why breezefield?

The love physics library is very flexible, but doing relatively simple things with it can be tedious. A good solution is the windfield library, but a few things didn’t quite sit right for me.

I’ve used windfield for a few practice projects, and I liked it very much. It makes protoyping faster, and massively reduces the time and mental effort spent putting together all the pieces of love.physics. so far however, I’ve encountered the occaisional issue that was tricky to track down due to (in particular) the collision-management system in place in windfield. When I needed to modify parts of it to my purposes, I found its size and complexity made it take a little longer than it could have with a simpler library.

Breezefield is a lightweight alternative that takes the parts that I liked best about windfield and leaves out what I felt held it back.

functionality

easily create physics objects (body + shape + fixture)

world:newCollider(<shape_type>, <shape_args>, <table_to_use>(optional))

query rectangle, circle, edge, or polygon areas

world:queryRectangleArea(x1, y1, x2, y2)

love.physics.<object> methods mapped to breezefield objects

Collider:<methodname> (e.g. get/setRestitution, get/setX, etc...)
World:<methodname> (e.g. update)

So you can make a collider move rightwards with

collider:setLinearVelocity(100, 0)

Collision handling

You can set collision events for a Collider by overwriting some methods:

`:enter(other, collision) called on each collider when two colliders come into contact
`:exit(other, collision) called on each collider when two colliders cease to be in contact
`:preSolve(other, collision)` called on each collider before their collision(e.g. bounce) has been resolved
`:postSolve(other, collision, normalimpulse, tangentimpulse)` called on each collider after their collision has been resolved

The collision argument to each will be the `love.physics.Contact` (https://love2d.org/wiki/Contact) object associated with the collision. A handy trick to prevent colliders from colliding with each other is to do `collision:setEnabled(False)` inside the preSolve method. You may notice that these correspond to the four callbacks in https://love2d.org/wiki/Tutorial:PhysicsCollisionCallbacks .

If you wish to handle collisions differently, you can also just overwrite those callbacks with `world:setCallbacks`

draw physics objects with one command

world:draw()

can be repurposed to draw in-game shapes/sprites!

Just redefine :draw on your collider objects, add other objects with :draw methods to world.colliders.

Call world:draw(<alpha>, true) to draw physics boundaries in addition to self-defined :draw methods

You can ensure some colliders are drawn over others with `Collider:setDrawOrder(number)`. Colliders with higher draw orders will be drawn over those with smaller draw orders. The default is 0, and the draw order can be negative.

access to love.physics objects if you have something more creative in mind

World._physworld contains the regular love.physics.world object. Collider.fixture, Collider.body, Collider.shape all contain the respective physics objects

please let me know if there are any issues

if there are any issues in breezefields implementation that complicates using love.physics together with it, let me know, or better yet, send a pull request

Installation

I reccomend you ensure you understand love.physics, as breezefield mostly just wraps that. You can start here. To install simply clone or download the repository and place breezefield anywhere in your lua path or in your project directory.

example/tutorial

Basics

setting up a basic world

bf = require("breezefield")

function love.load()
   world = bf.newWorld(0, 90.81, true)
   -- bf.World:new also works
   -- any function of love.physics.world should work on World
   print(world:getGravity())

   ground = bf.Collider.new(world, "Polygon",
				    {0, 550, 650, 550 , 650, 650, 0, 650})
   ground:setType("static")

   ball = bf.Collider.new(world, "Circle", 325, 325, 20)
   
   ball:setRestitution(0.8) -- any function of shape/body/fixture works
   block1 = bf.Collider.new(world, "Polygon", {150, 375, 250, 375,
					       250, 425, 150, 425})

end

forces, movement and control

any functions for shape, body, or fixture work on Colliders

function love.update(dt)
   world:update(dt)
   if love.keyboard.isDown("right") then
    ball:applyForce(400, 0)
  elseif love.keyboard.isDown("left") then
    ball:applyForce(-400, 0)
  elseif love.keyboard.isDown("up") then
    ball:setPosition(325, 325)
    ball:setLinearVelocity(0, 0) 
  elseif love.keyboard.isDown("down") then
     ball:applyForce(0, 600)
   end
end

easily draw physics

function love.draw()
   world:draw()
end

call functions on collision

default collision callbacks of World will locate the colliders from a fixture’s userData and call the relevant :enter :exit :postSolve or :preSolve method

pre: make that function and object to play with

little_ball = {}
little_ball.__index = little_ball
setmetatable(little_ball, bf.Collider) -- this is important
-- otherwise setting the new object's metatable to little_ball overwrites

function spawn_random_ball()
   little_ball.new(love.math.random(love.graphics.getWidth()), 0)
end

function little_ball.new(x, y)
   local n = bf.Collider.new(world, 'Circle', x, y, 5)
   setmetatable(n, little_ball)
   return n
end

define collision function

one feature is that any function callbacks returned by Collider:enter/exit/<post/pre>Solve are run in world:update() this lets us easily create and destroy objects in collision callbacks without crashing Box2D (love.physics’s backend)

 function ball:postSolve(other)
    if other == block1 then
	 -- creating Collder.new should never be called inside a callback
	 -- a limitation of (box2d)
	 -- instead, return a function to be called during World:update()
	 return spawn_random_ball -- see above for definition
    end
 end

change appearance of physics objects

simply define the :draw function on your collider (you can still access the default draw as :__draw__)

function little_ball:draw(alpha)
   love.graphics.setColor(0.9, 0.9, 0.0)
   love.graphics.circle('fill', self:getX(), self:getY(), self:getRadius())
end

query the world (supports rectangle, circle, polygon and edge)

function love.mousepressed()
   local x, y
   local radius = 30
   x, y = love.mouse.getPosition()
   local colls = world:queryCircleArea(x, y, radius)
   for _, collider in ipairs(colls) do
      if collider.identity == little_ball then
	 local dx = love.mouse.getX() - collider:getX()
	 local dy = love.mouse.getY() - collider:getY()
	 local power = -5
	 collider:applyLinearImpulse(power * dx, power * dy)
      end
   end
end

and after little_ball’s declaration

little_ball.identity = little_ball

define some form of collision filtering

for now, see: https://love2d.org/wiki/Contact:setEnabled https://love2d.org/wiki/Fixture:setFilterData

HDictus / breezefield