README.md

Lighter

A dynamic light / shadow casting library for Löve.

Installation

Clone the repo into your libs directory and require with

require 'path.to.lighter'

Usage

local Lighter = require 'path.to.lighter'

local lighter = Lighter()

local wall = {
    100, 100,
    300, 100,
    300, 300,
    100, 300
}

lighter:addPolygon(wall)

local lightX, lightY = 500, 500

-- addLight signature: (x,y,radius,r,g,b,a)
local light = lighter:addLight(lightX, lightY, 500, 1, 0.5, 0.5)

function love.update(dt)
    lightX, lightY = love.mouse.getPosition()
    lighter:updateLight(light, lightX, lightY)
end

function love.draw()
    love.graphics.polygon('fill', wall)
    lighter:drawLights()
end

-- Clean up
-- lighter:removeLight(light)
-- lighter:removePolygon(wall)

How to use in your game context with a darker global illumination:

(remember you can use any combination of additive & multiplicative blending to achieve a result you like)

-- Call after your light positions have been updated
function preDrawLights()
  love.graphics.setCanvas({ lightCanvas, stencil = true})
  love.graphics.clear(0.4, 0.4, 0.4) -- Global illumination level
  self.lighter:drawLights()
  love.graphics.setCanvas()
end

-- Call after you have drawn your scene (but before UI)
function drawLights()
  love.graphics.setBlendMode("multiply", "premultiplied")
  love.graphics.draw(lightCanvas)
  love.graphics.setBlendMode("alpha")
end

Function signatures of the public API:

    init = function(self, options)
    addLight = function(self, x, y, radius, r, g, b, a, gradientImage)
    updateLight = function(self, light, x, y, radius, r, g, b, a, gradientImage)
    removeLight = function(self, light)
    addPolygon = function(self, polygon)
    removePolygon = function(self, polygon)
    drawVisibilityPolygon = function(self, light)
    drawLights = function(self)

Credits:

• Helped me understand the premise and their code provided me with tons of helpful tips for getting this implemented: https://github.com/OneLoneCoder
• The actual page I ended up following to really get the idea: https://ncase.me/sight-and-light/

Screenshot of the library in use in a game

How it works under the hood

For each light we cast rays towards wall polygon corners (aka map features). Checks intersections. Builds a visibility polygon and uses it as the stencil for drawing the light.

As an optimization it uses a spatial map and calculates polygon bounding boxes on the fly so that only polygons within light radius get included in the visibility polygon calculations.