# World:rayCast

Available since LÖVE 0.8.0
This method is not supported in earlier versions.

Casts a ray and calls a function with the fixtures that intersect it. You cannot make any assumptions about the order of the callbacks.

Each time the function gets called, 6 arguments get passed to it. The first is the fixture intersecting the ray. The second and third are the coordinates of the intersection point. The fourth and fifth is the surface normal vector of the shape edge. The sixth argument is the position of the intersection on the ray as a number from 0 to 1 (or even higher if the ray length was changed with the return value).

The ray can be controlled with the return value. A positive value sets a new ray length where 1 is the default value. A value of 0 terminates the ray. If the callback function returns -1, the intersection gets ignored as if it didn't happen.

    function callback(fixture, x, y, xn, yn, fraction)
    	return 1
    end

## Function

### Synopsis

    World:rayCast( x1, y1, x2, y2, callback )

### Arguments

`number x1`
  The x position of the starting point of the ray.
`number y1`
  The y position of the starting point of the ray.
`number x2`
  The x position of the end point of the ray.
`number y2`
  The y position of the end point of the ray.
`function callback`
  This function gets six arguments and should return a number.

### Returns

Nothing.

## Notes

There is a bug in LÖVE 0.8.0 where the normal vector passed to the callback function gets scaled by love.physics.getMeter.

## Examples

### Casting a ray over some random shapes.

    function worldRayCastCallback(fixture, x, y, xn, yn, fraction)
    	local hit = {}
    	hit.fixture = fixture
    	hit.x, hit.y = x, y
    	hit.xn, hit.yn = xn, yn
    	hit.fraction = fraction

    	table.insert(Ray.hitList, hit)

    	return 1 -- Continues with ray cast through all shapes.
    end

    function createStuff()
    	-- Cleaning up the previous stuff.
    	for i = #Terrain.Stuff, 1, -1 do
    		Terrain.Stuff[i].Fixture:destroy()
    		Terrain.Stuff[i] = nil
    	end

    	-- Generates some random shapes.
    	for i = 1, 30 do
    		local p = {}

    		p.x, p.y = math.random(100, 700), math.random(100, 500)
    		local shapetype = math.random(3)
    		if shapetype == 1 then
    			local w, h, r = math.random() * 10 + 40, math.random() * 10 + 40, math.random() * math.pi * 2
    			p.Shape = love.physics.newRectangleShape(p.x, p.y, w, h, r)
    		elseif shapetype == 2 then
    			local a = math.random() * math.pi * 2
    			local x2, y2 = p.x + math.cos(a) * (math.random() * 30 + 20), p.y + math.sin(a) * (math.random() * 30 + 20)
    			p.Shape = love.physics.newEdgeShape(p.x, p.y, x2, y2)
    		else
    			local r = math.random() * 40 + 10
    			p.Shape = love.physics.newCircleShape(p.x, p.y, r)
    		end

    		p.Fixture = love.physics.newFixture(Terrain.Body, p.Shape)

    		Terrain.Stuff[i] = p
    	end
    end

    function love.keypressed()
    	createStuff()
    end

    function love.load()
    	-- Setting this to 1 to avoid all current scaling bugs.
    	love.physics.setMeter(1)

    	-- Start out with the same random stuff each start.
    	math.randomseed(0xfacef00d)

    	World = love.physics.newWorld()

    	Terrain = {}
    	Terrain.Body = love.physics.newBody(World, 0, 0, "static")
    	Terrain.Stuff = {}
    	createStuff()

    	Ray = {
    		x1 = 0,
    		y1 = 0,
    		x2 = 0,
    		y2 = 0,
    		hitList = {}
    	}
    end

    function love.update(dt)
    	local now = love.timer.getTime()

    	World:update(dt)

    	-- Clear fixture hit list.
    	Ray.hitList = {}

    	-- Calculate ray position.
    	local pos = (math.sin(now/4) + 1.2) * 0.4
    	Ray.x2, Ray.y2 = math.cos(pos * (math.pi/2)) * 1000, math.sin(pos * (math.pi/2)) * 1000

    	-- Cast the ray and populate the hitList table.
    	World:rayCast(Ray.x1, Ray.y1, Ray.x2, Ray.y2, worldRayCastCallback)
    end

    function love.draw()
    	-- Drawing the terrain.
    	love.graphics.setColor(255, 255, 255)
    	for i, v in ipairs(Terrain.Stuff) do
    		if v.Shape:getType() == "polygon" then
    			love.graphics.polygon("line", Terrain.Body:getWorldPoints( v.Shape:getPoints() ))
    		elseif v.Shape:getType() == "edge" then
    			love.graphics.line(Terrain.Body:getWorldPoints( v.Shape:getPoints() ))
    		else
    			local x, y = Terrain.Body:getWorldPoints(v.x, v.y)
    			love.graphics.circle("line", x, y, v.Shape:getRadius())
    		end
    	end

    	-- Drawing the ray.
    	love.graphics.setLineWidth(3)
    	love.graphics.setColor(255, 255, 255, 100)
    	love.graphics.line(Ray.x1, Ray.y1, Ray.x2, Ray.y2)
    	love.graphics.setLineWidth(1)

    	-- Drawing the intersection points and normal vectors if there were any.
    	for i, hit in ipairs(Ray.hitList) do
    		love.graphics.setColor(255, 0, 0)
    		love.graphics.print(i, hit.x, hit.y) -- Prints the hit order besides the point.
    		love.graphics.circle("line", hit.x, hit.y, 3)
    		love.graphics.setColor(0, 255, 0)
    		love.graphics.line(hit.x, hit.y, hit.x + hit.xn * 25, hit.y + hit.yn * 25)
    	end
    end

Screenshot of the example.

## See Also

- World

##

Category:

- Functions