diff --git a/ui/f32/f32.go b/ui/f32/f32.go
index 6a01a91e..a01d63e5 100644
--- a/ui/f32/f32.go
+++ b/ui/f32/f32.go
@@ -1,39 +1,55 @@
 // SPDX-License-Identifier: Unlicense OR MIT
+/*
+Package f32 is a float32 implementation of package image's
+Point and Rectangle
 
+The coordinate space has the origin in the top left
+corner with the axes extending right and down.
+*/
 package f32
 
+// A Point is a two dimensional point.
 type Point struct {
 	X, Y float32
 }
 
+// A Rectangle contains the points (X, Y) where Min.X <= X < Max.X,
+// Min.Y <= Y < Max.Y.
 type Rectangle struct {
 	Min, Max Point
 }
 
+// Add return the point p+p2.
 func (p Point) Add(p2 Point) Point {
 	return Point{X: p.X + p2.X, Y: p.Y + p2.Y}
 }
 
+// Sub returns the vector p-p2.
 func (p Point) Sub(p2 Point) Point {
 	return Point{X: p.X - p2.X, Y: p.Y - p2.Y}
 }
 
+// Mul returns p scaled by s.
 func (p Point) Mul(s float32) Point {
 	return Point{X: p.X * s, Y: p.Y * s}
 }
 
+// Size returns r's width and height.
 func (r Rectangle) Size() Point {
 	return Point{X: r.Dx(), Y: r.Dy()}
 }
 
+// Dx returns r's width.
 func (r Rectangle) Dx() float32 {
 	return r.Max.X - r.Min.X
 }
 
+// Dy returns r's Height.
 func (r Rectangle) Dy() float32 {
 	return r.Max.Y - r.Min.Y
 }
 
+// Intersect returns the intersection of r and s.
 func (r Rectangle) Intersect(s Rectangle) Rectangle {
 	if r.Min.X < s.Min.X {
 		r.Min.X = s.Min.X
@@ -50,6 +66,7 @@ func (r Rectangle) Intersect(s Rectangle) Rectangle {
 	return r
 }
 
+// Union returns the union of r and s.
 func (r Rectangle) Union(s Rectangle) Rectangle {
 	if r.Min.X > s.Min.X {
 		r.Min.X = s.Min.X
@@ -66,6 +83,8 @@ func (r Rectangle) Union(s Rectangle) Rectangle {
 	return r
 }
 
+// Canon returns the canonical version of r, where Min is to
+// the upper left of Max.
 func (r Rectangle) Canon() Rectangle {
 	if r.Max.X < r.Min.X {
 		r.Min.X, r.Max.X = r.Max.X, r.Min.X
@@ -76,10 +95,12 @@ func (r Rectangle) Canon() Rectangle {
 	return r
 }
 
+// Empty reports whether r represents the empty area.
 func (r Rectangle) Empty() bool {
 	return r.Min.X >= r.Max.X || r.Min.Y >= r.Max.Y
 }
 
+// Add offsets r with the vector p.
 func (r Rectangle) Add(p Point) Rectangle {
 	return Rectangle{
 		Point{r.Min.X + p.X, r.Min.Y + p.Y},
@@ -87,6 +108,7 @@ func (r Rectangle) Add(p Point) Rectangle {
 	}
 }
 
+// Sub offsets r with the vector -p.
 func (r Rectangle) Sub(p Point) Rectangle {
 	return Rectangle{
 		Point{r.Min.X - p.X, r.Min.Y - p.Y},