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.

Synopsis

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

Arguments

Fixture fixture

The fixture intersecting the ray.

number x

The x position of the intersection point.

number y

The y position of the intersection point.

number xn

The x value of the surface normal vector of the shape edge.

number yn

The y value of the surface normal vector of the shape edge.

number fraction

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).

Returns

number

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.

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.

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.

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

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