diff --git a/engine/parallax.go b/engine/parallax.go
index df58728..7eca0f5 100644
--- a/engine/parallax.go
+++ b/engine/parallax.go
@@ -17,16 +17,17 @@ func init() {
 	gob.Register(&Parallax{})
 }
 
-// Parallax is a container that changes its transform based on the position of a
+// Parallax is a container that translates based on the position of a
 // camera, intended to produce a "parallax" like effect.
 type Parallax struct {
 	CameraID string
-	Factor   float64 // how much to change in response to the camera
+	Factor   float64 // how much to translate in response to the camera
 	Child    interface{}
 
 	camera *Camera
 }
 
+// Prepare obtains a reference to the camera.
 func (p *Parallax) Prepare(game *Game) error {
 	c, ok := game.Component(p.CameraID).(*Camera)
 	if !ok {
@@ -36,8 +37,10 @@ func (p *Parallax) Prepare(game *Game) error {
 	return nil
 }
 
+// Scan returns the child component.
 func (p *Parallax) Scan() []interface{} { return []interface{}{p.Child} }
 
+// Transform returns a GeoM translation of Factor * camera.Centre.
 func (p *Parallax) Transform() (opts ebiten.DrawImageOptions) {
 	x, y := float2(p.camera.Centre)
 	opts.GeoM.Translate(x*p.Factor, y*p.Factor)