# BezierCurve:getDerivative

 Available since LÖVE 0.9.0 This function is not supported in earlier versions.

Get the derivative of the Bézier curve.

This function can be used to rotate sprites moving along a curve in the direction of the movement and compute the direction perpendicular to the curve at some parameter t.

## Function

### Synopsis

```derivative = BezierCurve:getDerivative()
```

None.

### Returns

`BezierCurve derivative`
The derivative curve.

## Example

### Position a sprite along a Bézier-curve.

```curve      = love.math.newBezierCurve({25,25,75,50,125,25})
derivative = curve:getDerivative()
sprite     = love.graphics.newImage('sprite.png') -- to demonstrate orientation; assuming the sprite's front is upwards.

local t = 0.0 -- range: [0,1]
function love.update(dt)
t = (t + dt / 10) % 1.0
end

function love.draw()
local ex,ey = curve:evaluate(t)
local dx,dy = derivative:evaluate(t)
-- If the sprite were facing to the right, the +math.pi/2 part would not be needed.
love.graphics.draw(sprite, ex, ey, math.atan2(dy,dx)+math.pi/2, 1, 1, sprite:getWidth()/2, sprite:getHeight()/2)
end
```