Fixture:rayCast

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

Casts a ray against the shape of the fixture and returns the surface normal vector and the line position where the ray hit. If the ray missed the shape, nil will be returned.

The ray starts on the first point of the input line and goes towards the second point of the line. The fourth argument is the maximum distance the ray is going to travel as a scale factor of the input line length.

The childIndex parameter is used to specify which child of a parent shape, such as a ChainShape, will be ray casted. For ChainShapes, the index of 1 is the first edge on the chain. Ray casting a parent shape will only test the child specified so if you want to test every shape of the parent, you must loop through all of its children.

The world position of the impact can be calculated by multiplying the line vector with the third return value and adding it to the line starting point.

hitx, hity = x1 + (x2 - x1) * fraction, y1 + (y2 - y1) * fraction


O.png There is a bug in 0.8.0 where the normal vector returned by this function gets scaled by love.physics.getMeter.  

Function

Synopsis

xn, yn, fraction = Fixture:rayCast( x1, y1, x2, y2, maxFraction, childIndex )

Arguments

number x1
The x position of the input line starting point.
number y1
The y position of the input line starting point.
number x2
The x position of the input line end point.
number y2
The y position of the input line end point.
number maxFraction
Ray length parameter.
number childIndex (1)
The index of the child the ray gets cast against.

Returns

number xn
The x component of the normal vector of the edge where the ray hit the shape.
number yn
The y component of the normal vector of the edge where the ray hit the shape.
number fraction
The position on the input line where the intersection happened as a factor of the line length.

Examples

Casting 2 different rays against a box.

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

    World = love.physics.newWorld()

    Box = {}
    Box.Body = love.physics.newBody(World, 400, 300, "dynamic")
    Box.Shape = love.physics.newRectangleShape(150, 150)
    Box.Fixture = love.physics.newFixture(Box.Body, Box.Shape)

    -- Giving the box a gentle spin.
    Box.Body:setAngularVelocity(0.5)

    Ray1 = {
        point1 = {},
        point2 = {},
    }
    Ray1.point1.x, Ray1.point1.y = 50, 50
    Ray1.point2.x, Ray1.point2.y = 400, 300
    Ray1.scale = 1

    Ray2 = {
        point1 = {},
        point2 = {},
    }
    Ray2.point1.x, Ray2.point1.y = 500, 400
    Ray2.point2.x, Ray2.point2.y = Ray2.point1.x + math.cos(math.pi*1.45), Ray2.point1.y + math.sin(math.pi*1.45)
    Ray2.scale = 150
end

function love.update(dt)
    World:update(dt)
end

function love.draw()
    -- Drawing the box.
    love.graphics.setColor(255, 255, 255)
    love.graphics.polygon("line", Box.Body:getWorldPoints( Box.Shape:getPoints() ))

    -- Drawing the input lines of the rays and the reach of ray 2 in gray.
    love.graphics.setLineWidth(3)
    love.graphics.setColor(50, 50, 50)
    love.graphics.line(Ray2.point1.x, Ray2.point1.y, Ray2.point1.x + (Ray2.point2.x - Ray2.point1.x) * Ray2.scale, Ray2.point1.y + (Ray2.point2.y - Ray2.point1.y) * Ray2.scale)
    love.graphics.setColor(255, 255, 255)
    love.graphics.line(Ray1.point1.x, Ray1.point1.y, Ray1.point2.x, Ray1.point2.y)
    love.graphics.line(Ray2.point1.x, Ray2.point1.y, Ray2.point2.x, Ray2.point2.y)
    love.graphics.setLineWidth(1)

    -- Remember that the ray cast can return nil if it hits nothing.
    local r1nx, r1ny, r1f = Box.Fixture:rayCast(Ray1.point1.x, Ray1.point1.y, Ray1.point2.x, Ray1.point2.y, Ray1.scale)
    local r2nx, r2ny, r2f = Box.Fixture:rayCast(Ray2.point1.x, Ray2.point1.y, Ray2.point2.x, Ray2.point2.y, Ray2.scale)

    if r1nx then
        -- Calculating the world position where the ray hit.
        local r1HitX = Ray1.point1.x + (Ray1.point2.x - Ray1.point1.x) * r1f
        local r1HitY = Ray1.point1.y + (Ray1.point2.y - Ray1.point1.y) * r1f

        -- Drawing the ray from the starting point to the position on the shape.
        love.graphics.setColor(255, 0, 0)
        love.graphics.line(Ray1.point1.x, Ray1.point1.y, r1HitX, r1HitY)

        -- We also get the surface normal of the edge the ray hit. Here drawn in green
        love.graphics.setColor(0, 255, 0)
        love.graphics.line(r1HitX, r1HitY, r1HitX + r1nx * 25, r1HitY + r1ny * 25)
    end

    if r2nx then
        -- Calculating the world position where the ray hit.
        local r2HitX = Ray2.point1.x + (Ray2.point2.x - Ray2.point1.x) * r2f
        local r2HitY = Ray2.point1.y + (Ray2.point2.y - Ray2.point1.y) * r2f

        -- Drawing the ray from the starting point to the position on the shape.
        love.graphics.setColor(255, 0, 0)
        love.graphics.line(Ray2.point1.x, Ray2.point1.y, r2HitX, r2HitY)

        -- We also get the surface normal of the edge the ray hit. Here drawn in green
        love.graphics.setColor(0, 255, 0)
        love.graphics.line(r2HitX, r2HitY, r2HitX + r2nx * 25, r2HitY + r2ny * 25)
    end
end
Screenshot of this example

See Also


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