Trouble With Shadows / Raycasting with Physics and Shaders

General discussion about LÖVE, Lua, game development, puns, and unicorns.
Post Reply
User avatar
Posts: 16
Joined: Tue Feb 03, 2015 5:24 am

Trouble With Shadows / Raycasting with Physics and Shaders

Post by harrison » Mon Sep 03, 2018 9:59 pm

I am trying to set up a extremely basic shadow system using physics (for raycasting shapes) and shaders (for the shadows). This is what I have so far but I am stuck on a couple things.

1. How do I get my array of shadow/bright from lua into the shader? I have heard of Shader:send() but it says it only supports vectors of up to 4 variables. I suppose I could try to send a single extremely long number (like 01001111000...) instead of an array, but that sounds very inefficient.

2. I am getting a strange error with physics (and googling it doesn't help):

Code: Select all


main.lua:33: Box2D assertion failed: r.LengthSquared() > 0.0f


[C]: in function 'rayCast'
main.lua:33: in function 'draw'
[C]: in function 'xpcall'
main.lua (should be able to run on its own but definitely has some bugs)

Code: Select all

function love.load()
	world = love.physics.newWorld(0,0,true)
	objects = {}
	objects.obstacle = {}
	objects.obstacle.body = love.physics.newBody(world, 200, 200)
	objects.obstacle.shape = love.physics.newRectangleShape(50, 50)
	objects.obstacle.fixture = love.physics.newFixture(objects.obstacle.body, objects.obstacle.shape)
	objects.lightSource = {}
	objects.lightSource.body = love.physics.newBody(world, 350, 250)
	objects.lightSource.shape = love.physics.newCircleShape(10)
	objects.lightSource.fixture = love.physics.newFixture(objects.obstacle.body, objects.obstacle.shape)

	myShader =[[
		vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords ){
			vec4 pixel = Texel(texture, texture_coords);
			if (true){ 
				return vec4(pixel.r, pixel.g, pixel.b, 1);
			else {
				return vec4(pixel.r, pixel.g, pixel.b,0);

function love.draw()
	--perform raytracing for each pixel
	isPixelLit = {}
	for y=0, do
		for x=0, do
			collision = false
			world:rayCast(objects.lightSource.body:getX(), objects.lightSource.body:getY(), x, y, worldRayCastCallback)
			if(collision) then
				isPixelLit[#isPixelLit+1] = 0
				isPixelLit[#isPixelLit+1] = 1
	--send the pixel table to the shader
	--not sure how to do this... --draw something here, 0, 0)"fill", objects.lightSource.body:getX(), objects.lightSource.body:getY(), objects.lightSource.shape:getRadius()), 1, 0)"fill", objects.obstacle.body:getWorldPoints(objects.obstacle.shape:getPoints())) --disable the shader for the remaining objects to draw

function love.update(dt)

function worldRayCastCallback()
	collision = true
	return 1
I was hoping somebody could help me out with these two issues.
Also, is this a terrible way to add shadows to my game? I feel like there is probably a much better/cleaner way of doing this.

User avatar
Posts: 59
Joined: Thu Feb 22, 2018 3:15 pm

Re: Trouble With Shadows / Raycasting with Physics and Shaders

Post by NotARaptor » Tue Sep 04, 2018 8:52 am

Can't help you with point 2, but for point 1, store the array data in a texture - it can be 1 pixel high and n pixels wide, send that to the shader with shader:send. The shader can then read it using the Texel() function.

User avatar
Inner party member
Posts: 1940
Joined: Tue Dec 06, 2011 7:11 pm
Location: Italy

Re: Trouble With Shadows / Raycasting with Physics and Shaders

Post by Nixola » Wed Sep 05, 2018 12:07 pm

For point 2, sounds like you're casting a ray from a point to the same point? Maybe you should add a check against that
lf = love.filesystem
ls = love.sound
la =
lp = love.physics
lt = love.thread
li = love.image
lg =

Post Reply

Who is online

Users browsing this forum: Google [Bot] and 15 guests