diff --git a/app/app.go b/app/app.go
index c1862d6e..c660bee2 100644
--- a/app/app.go
+++ b/app/app.go
@@ -10,7 +10,7 @@ import (
 	"strings"
 	"time"
 
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 // An UpdateEvent is generated when a Window's Update
@@ -39,7 +39,7 @@ type DestroyEvent struct {
 // system decoration such as translucent
 // system bars and software keyboards.
 type Insets struct {
-	Top, Bottom, Left, Right ui.Value
+	Top, Bottom, Left, Right unit.Value
 }
 
 // A StageEvent is generated whenever the stage of a
@@ -146,7 +146,7 @@ func Main() {
 	main()
 }
 
-// Config implements the ui.Config interface.
+// Config implements the layout.Config interface.
 type Config struct {
 	// Device pixels per dp.
 	pxPerDp float32
@@ -159,14 +159,14 @@ func (c *Config) Now() time.Time {
 	return c.now
 }
 
-func (c *Config) Px(v ui.Value) int {
+func (c *Config) Px(v unit.Value) int {
 	var r float32
 	switch v.U {
-	case ui.UnitPx:
+	case unit.UnitPx:
 		r = v.V
-	case ui.UnitDp:
+	case unit.UnitDp:
 		r = c.pxPerDp * v.V
-	case ui.UnitSp:
+	case unit.UnitSp:
 		r = c.pxPerSp * v.V
 	default:
 		panic("unknown unit")
diff --git a/app/doc.go b/app/doc.go
index 6eb37edc..95a7b84f 100644
--- a/app/doc.go
+++ b/app/doc.go
@@ -18,7 +18,7 @@ contents and state.
 
 For example:
 
-	import "gioui.org/ui"
+	import "gioui.org/unit"
 
 	w := app.NewWindow()
 	for e := range w.Events() {
diff --git a/app/os_android.go b/app/os_android.go
index e4c05685..c77b9cf9 100644
--- a/app/os_android.go
+++ b/app/os_android.go
@@ -27,7 +27,7 @@ import (
 	"gioui.org/f32"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 type window struct {
diff --git a/app/os_ios.go b/app/os_ios.go
index 65f07906..65dd198e 100644
--- a/app/os_ios.go
+++ b/app/os_ios.go
@@ -25,7 +25,7 @@ import (
 	"gioui.org/f32"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 type window struct {
diff --git a/app/os_wayland.go b/app/os_wayland.go
index bf3c17ae..248c7317 100644
--- a/app/os_wayland.go
+++ b/app/os_wayland.go
@@ -583,8 +583,7 @@ func (w *window) flushFling() {
 	w.fling.yExtrapolation = fling.Extrapolation{}
 	vel := float32(math.Sqrt(float64(estx.Velocity*estx.Velocity + esty.Velocity*esty.Velocity)))
 	_, _, c := w.config()
-	c.now = time.Now()
-	if !w.fling.anim.Start(&c, vel) {
+	if !w.fling.anim.Start(&c, time.Now(), vel) {
 		return
 	}
 	invDist := 1 / vel
diff --git a/app/window.go b/app/window.go
index 361f3b90..f0302e51 100644
--- a/app/window.go
+++ b/app/window.go
@@ -13,7 +13,7 @@ import (
 	"gioui.org/io/event"
 	"gioui.org/io/profile"
 	"gioui.org/op"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 // WindowOption configures a Window.
@@ -22,7 +22,7 @@ type WindowOption struct {
 }
 
 type windowOptions struct {
-	Width, Height ui.Value
+	Width, Height unit.Value
 	Title         string
 }
 
@@ -86,8 +86,8 @@ var ackEvent event.Event
 // BUG: Calling NewWindow more than once is not yet supported.
 func NewWindow(options ...WindowOption) *Window {
 	opts := &windowOptions{
-		Width:  ui.Dp(800),
-		Height: ui.Dp(600),
+		Width:  unit.Dp(800),
+		Height: unit.Dp(600),
 		Title:  "Gio",
 	}
 
@@ -339,7 +339,7 @@ func WithTitle(t string) WindowOption {
 }
 
 // WithWidth returns an option that sets the window width.
-func WithWidth(w ui.Value) WindowOption {
+func WithWidth(w unit.Value) WindowOption {
 	if w.V <= 0 {
 		panic("width must be larger than or equal to 0")
 	}
@@ -351,7 +351,7 @@ func WithWidth(w ui.Value) WindowOption {
 }
 
 // WithHeight returns an option that sets the window height.
-func WithHeight(h ui.Value) WindowOption {
+func WithHeight(h unit.Value) WindowOption {
 	if h.V <= 0 {
 		panic("height must be larger than or equal to 0")
 	}
diff --git a/cmd/gogio/js_test.go b/cmd/gogio/js_test.go
index 9241891b..5a4749f7 100644
--- a/cmd/gogio/js_test.go
+++ b/cmd/gogio/js_test.go
@@ -15,7 +15,7 @@ import (
 
 	"github.com/chromedp/chromedp"
 
-	_ "gioui.org/ui" // the build tool adds it to go.mod, so keep it there
+	_ "gioui.org/unit" // the build tool adds it to go.mod, so keep it there
 )
 
 func TestJSOnChrome(t *testing.T) {
diff --git a/gesture/gesture.go b/gesture/gesture.go
index d914ea91..9449825d 100644
--- a/gesture/gesture.go
+++ b/gesture/gesture.go
@@ -11,13 +11,14 @@ package gesture
 
 import (
 	"math"
+	"time"
 
 	"gioui.org/f32"
 	"gioui.org/internal/fling"
 	"gioui.org/io/event"
 	"gioui.org/io/pointer"
 	"gioui.org/op"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 // Click detects click gestures in the form
@@ -93,7 +94,7 @@ const (
 	StateFlinging
 )
 
-var touchSlop = ui.Dp(3)
+var touchSlop = unit.Dp(3)
 
 // Add the handler to the operation list to receive click events.
 func (c *Click) Add(ops *op.Ops) {
@@ -156,7 +157,7 @@ func (s *Scroll) Stop() {
 
 // Scroll detects the scrolling distance from the available events and
 // ongoing fling gestures.
-func (s *Scroll) Scroll(cfg ui.Config, q event.Queue, axis Axis) int {
+func (s *Scroll) Scroll(cfg unit.Converter, q event.Queue, t time.Time, axis Axis) int {
 	if s.axis != axis {
 		s.axis = axis
 		return 0
@@ -185,7 +186,7 @@ func (s *Scroll) Scroll(cfg ui.Config, q event.Queue, axis Axis) int {
 			}
 			fling := s.estimator.Estimate()
 			if slop, d := float32(cfg.Px(touchSlop)), fling.Distance; d < -slop || d > slop {
-				s.flinger.Start(cfg, fling.Velocity)
+				s.flinger.Start(cfg, t, fling.Velocity)
 			}
 			fallthrough
 		case pointer.Cancel:
@@ -221,7 +222,7 @@ func (s *Scroll) Scroll(cfg ui.Config, q event.Queue, axis Axis) int {
 			}
 		}
 	}
-	total += s.flinger.Tick(cfg.Now())
+	total += s.flinger.Tick(t)
 	return total
 }
 
diff --git a/internal/fling/animation.go b/internal/fling/animation.go
index 6d9a004d..66dfb880 100644
--- a/internal/fling/animation.go
+++ b/internal/fling/animation.go
@@ -7,7 +7,7 @@ import (
 	"runtime"
 	"time"
 
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 type Animation struct {
@@ -21,8 +21,8 @@ type Animation struct {
 
 var (
 	// Pixels/second.
-	minFlingVelocity = ui.Dp(50)
-	maxFlingVelocity = ui.Dp(8000)
+	minFlingVelocity = unit.Dp(50)
+	maxFlingVelocity = unit.Dp(8000)
 )
 
 const (
@@ -31,7 +31,7 @@ const (
 
 // Start a fling given a starting velocity. Returns whether a
 // fling was started.
-func (f *Animation) Start(c ui.Config, velocity float32) bool {
+func (f *Animation) Start(c unit.Converter, now time.Time, velocity float32) bool {
 	min := float32(c.Px(minFlingVelocity))
 	v := velocity
 	if -min <= v && v <= min {
@@ -43,7 +43,7 @@ func (f *Animation) Start(c ui.Config, velocity float32) bool {
 	} else if v < -max {
 		v = -max
 	}
-	f.init(c.Now(), v)
+	f.init(now, v)
 	return true
 }
 
diff --git a/layout/doc.go b/layout/doc.go
index aedb1c69..12bc7c7a 100644
--- a/layout/doc.go
+++ b/layout/doc.go
@@ -17,7 +17,7 @@ For example, to add space above a widget:
 	gtx.Reset(...)
 
 	// Configure a top inset.
-	inset := layout.Inset{Top: ui.Dp(8), ...}
+	inset := layout.Inset{Top: unit.Dp(8), ...}
 	// Use the inset to lay out a widget.
 	inset.Layout(gtx, func() {
 		// Lay out widget and determine its size given the constraints.
diff --git a/layout/layout.go b/layout/layout.go
index 7cb9715c..4f890bb8 100644
--- a/layout/layout.go
+++ b/layout/layout.go
@@ -4,10 +4,11 @@ package layout
 
 import (
 	"image"
+	"time"
 
 	"gioui.org/io/event"
 	"gioui.org/op"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 // Constraints represent a set of acceptable ranges for
@@ -52,11 +53,20 @@ type Context struct {
 	// operation.
 	Dimensions Dimensions
 
-	ui.Config
+	Config
 	event.Queue
 	*op.Ops
 }
 
+// Config define the essential properties of
+// the environment.
+type Config interface {
+	// Now returns the current animation time.
+	Now() time.Time
+
+	unit.Converter
+}
+
 const (
 	Start Alignment = iota
 	End
@@ -93,7 +103,7 @@ func (s *Context) Layout(cs Constraints, w Widget) Dimensions {
 }
 
 // Reset the context.
-func (c *Context) Reset(cfg ui.Config, cs Constraints) {
+func (c *Context) Reset(cfg Config, cs Constraints) {
 	c.Constraints = cs
 	c.Dimensions = Dimensions{}
 	c.Config = cfg
@@ -129,7 +139,7 @@ func RigidConstraints(size image.Point) Constraints {
 
 // Inset adds space around a widget.
 type Inset struct {
-	Top, Right, Bottom, Left ui.Value
+	Top, Right, Bottom, Left unit.Value
 }
 
 // Align aligns a widget in the available space.
@@ -171,7 +181,7 @@ func (in Inset) Layout(gtx *Context, w Widget) {
 
 // UniformInset returns an Inset with a single inset applied to all
 // edges.
-func UniformInset(v ui.Value) Inset {
+func UniformInset(v unit.Value) Inset {
 	return Inset{Top: v, Right: v, Bottom: v, Left: v}
 }
 
diff --git a/layout/layout_test.go b/layout/layout_test.go
index 5c5a8dd5..0524e0d2 100644
--- a/layout/layout_test.go
+++ b/layout/layout_test.go
@@ -7,7 +7,7 @@ import (
 
 	"gioui.org/io/event"
 	"gioui.org/layout"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 type queue struct{}
@@ -26,7 +26,7 @@ func ExampleInset() {
 	gtx.Reset(cfg, cs)
 
 	// Inset all edges by 10.
-	inset := layout.UniformInset(ui.Dp(10))
+	inset := layout.UniformInset(unit.Dp(10))
 	inset.Layout(gtx, func() {
 		// Lay out a 50x50 sized widget.
 		layoutWidget(gtx, 50, 50)
@@ -146,7 +146,7 @@ func (config) Now() time.Time {
 	return time.Now()
 }
 
-func (config) Px(v ui.Value) int {
+func (config) Px(v unit.Value) int {
 	return int(v.V + .5)
 }
 
diff --git a/layout/list.go b/layout/list.go
index 37f03b09..7a60cfeb 100644
--- a/layout/list.go
+++ b/layout/list.go
@@ -110,7 +110,7 @@ func (l *List) Dragging() bool {
 }
 
 func (l *List) update() {
-	d := l.scroll.Scroll(l.ctx.Config, l.ctx.Queue, gesture.Axis(l.Axis))
+	d := l.scroll.Scroll(l.ctx.Config, l.ctx.Queue, l.ctx.Now(), gesture.Axis(l.Axis))
 	l.scrollDelta = d
 	l.offset += d
 }
diff --git a/op/op.go b/op/op.go
index dace4a40..de851ef1 100644
--- a/op/op.go
+++ b/op/op.go
@@ -15,7 +15,7 @@ to a ui/app.Window's Update method.
 
 Drawing a colored square:
 
-	import "gioui.org/ui"
+	import "gioui.org/unit"
 	import "gioui.org/app"
 	import "gioui.org/op/paint"
 
diff --git a/text/editor.go b/text/editor.go
index 59c93fc4..74448c9f 100644
--- a/text/editor.go
+++ b/text/editor.go
@@ -16,7 +16,7 @@ import (
 	"gioui.org/layout"
 	"gioui.org/op"
 	"gioui.org/op/paint"
-	"gioui.org/ui"
+	"gioui.org/unit"
 
 	"golang.org/x/image/math/fixed"
 )
@@ -88,7 +88,7 @@ const (
 // Event returns the next available editor event, or false if none are available.
 func (e *Editor) Event(gtx *layout.Context) (EditorEvent, bool) {
 	// Crude configuration change detection.
-	if scale := gtx.Px(ui.Sp(100)); scale != e.oldScale {
+	if scale := gtx.Px(unit.Sp(100)); scale != e.oldScale {
 		e.invalidate()
 		e.oldScale = scale
 	}
@@ -102,7 +102,7 @@ func (e *Editor) Event(gtx *layout.Context) (EditorEvent, bool) {
 		axis = gesture.Vertical
 		smin, smax = sbounds.Min.Y, sbounds.Max.Y
 	}
-	sdist := e.scroller.Scroll(gtx.Config, gtx.Queue, axis)
+	sdist := e.scroller.Scroll(gtx.Config, gtx.Queue, gtx.Now(), axis)
 	var soff int
 	if e.SingleLine {
 		e.scrollOff.X += sdist
@@ -167,8 +167,8 @@ func (e *Editor) editorEvent(gtx *layout.Context) (EditorEvent, bool) {
 	return nil, false
 }
 
-func (e *Editor) caretWidth(c ui.Config) fixed.Int26_6 {
-	oneDp := c.Px(ui.Dp(1))
+func (e *Editor) caretWidth(c unit.Converter) fixed.Int26_6 {
+	oneDp := c.Px(unit.Dp(1))
 	return fixed.Int26_6(oneDp * 64)
 }
 
@@ -182,7 +182,7 @@ func (e *Editor) Layout(gtx *layout.Context) {
 	cs := gtx.Constraints
 	for _, ok := e.Event(gtx); ok; _, ok = e.Event(gtx) {
 	}
-	twoDp := gtx.Px(ui.Dp(2))
+	twoDp := gtx.Px(unit.Dp(2))
 	e.padLeft, e.padRight = twoDp, twoDp
 	maxWidth := cs.Width.Max
 	if e.SingleLine {
@@ -275,7 +275,7 @@ func (e *Editor) Layout(gtx *layout.Context) {
 	stack.Pop()
 
 	baseline := e.padTop + e.dims.Baseline
-	pointerPadding := gtx.Px(ui.Dp(4))
+	pointerPadding := gtx.Px(unit.Dp(4))
 	r := image.Rectangle{Max: e.viewSize}
 	r.Min.X -= pointerPadding
 	r.Min.Y -= pointerPadding
@@ -563,7 +563,7 @@ func (e *Editor) moveEnd() {
 	e.carXOff = l.Width + a - x
 }
 
-func (e *Editor) scrollToCaret(c ui.Config) {
+func (e *Editor) scrollToCaret(c unit.Converter) {
 	carWidth := e.caretWidth(c)
 	carLine, _, x, y := e.layoutCaret()
 	l := e.lines[carLine]
diff --git a/text/shape/measure.go b/text/shape/measure.go
index 1c832dbe..df5643f8 100644
--- a/text/shape/measure.go
+++ b/text/shape/measure.go
@@ -14,7 +14,7 @@ import (
 	"gioui.org/op"
 	"gioui.org/op/paint"
 	"gioui.org/text"
-	"gioui.org/ui"
+	"gioui.org/unit"
 	"golang.org/x/image/font"
 	"golang.org/x/image/font/sfnt"
 	"golang.org/x/image/math/fixed"
@@ -22,7 +22,7 @@ import (
 
 // Faces is a cache of text layouts and paths.
 type Faces struct {
-	config      ui.Config
+	config      unit.Converter
 	faceCache   map[faceKey]*Face
 	layoutCache map[layoutKey]cachedLayout
 	pathCache   map[pathKey]cachedPath
@@ -53,19 +53,19 @@ type pathKey struct {
 
 type faceKey struct {
 	font *sfnt.Font
-	size ui.Value
+	size unit.Value
 }
 
 // Face is a cached implementation of text.Face.
 type Face struct {
 	faces *Faces
-	size  ui.Value
+	size  unit.Value
 	font  *opentype
 }
 
 // Reset the cache, discarding any measures or paths that
 // haven't been used since the last call to Reset.
-func (f *Faces) Reset(c ui.Config) {
+func (f *Faces) Reset(c unit.Converter) {
 	f.config = c
 	f.init()
 	for pk, p := range f.pathCache {
@@ -87,7 +87,7 @@ func (f *Faces) Reset(c ui.Config) {
 }
 
 // For returns a Face for the given font and size.
-func (f *Faces) For(fnt *sfnt.Font, size ui.Value) *Face {
+func (f *Faces) For(fnt *sfnt.Font, size unit.Value) *Face {
 	f.init()
 	fk := faceKey{fnt, size}
 	if f, exist := f.faceCache[fk]; exist {
diff --git a/ui/doc.go b/ui/doc.go
deleted file mode 100644
index 65ee355d..00000000
--- a/ui/doc.go
+++ /dev/null
@@ -1,25 +0,0 @@
-// SPDX-License-Identifier: Unlicense OR MIT
-
-/*
-Package ui defines operations buffers, units and common operations
-for GUI programs written with the Gio module.
-
-Units
-
-A Value is a value with a Unit attached.
-
-Device independent pixel, or dp, is the unit for sizes independent of
-the underlying display device.
-
-Scaled pixels, or sp, is the unit for text sizes. An sp is like dp with
-text scaling applied.
-
-Finally, pixels, or px, is the unit for display dependent pixels. Their
-size vary between platforms and displays.
-
-To maintain a constant visual size across platforms and displays, always
-use dps or sps to define user interfaces. Only use pixels for derived
-values.
-
-*/
-package ui
diff --git a/ui/ui.go b/ui/ui.go
deleted file mode 100644
index 8f083d4f..00000000
--- a/ui/ui.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// SPDX-License-Identifier: Unlicense OR MIT
-
-package ui
-
-import (
-	"time"
-)
-
-// Config define the essential properties of
-// the environment.
-type Config interface {
-	// Now returns the current animation time.
-	Now() time.Time
-	// Px converts a Value to pixels.
-	Px(v Value) int
-}
diff --git a/ui/unit.go b/unit/unit.go
similarity index 65%
rename from ui/unit.go
rename to unit/unit.go
index 418fbfdf..0fdc60a1 100644
--- a/ui/unit.go
+++ b/unit/unit.go
@@ -1,6 +1,26 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-package ui
+/*
+
+Package unit implements device independent units and values.
+
+A Value is a value with a Unit attached.
+
+Device independent pixel, or dp, is the unit for sizes independent of
+the underlying display device.
+
+Scaled pixels, or sp, is the unit for text sizes. An sp is like dp with
+text scaling applied.
+
+Finally, pixels, or px, is the unit for display dependent pixels. Their
+size vary between platforms and displays.
+
+To maintain a constant visual size across platforms and displays, always
+use dps or sps to define user interfaces. Only use pixels for derived
+values.
+
+*/
+package unit
 
 import "fmt"
 
@@ -13,6 +33,11 @@ type Value struct {
 // Unit represents a unit for a Value.
 type Unit uint8
 
+// Converter converts Values to pixels.
+type Converter interface {
+	Px(v Value) int
+}
+
 const (
 	// UnitPx represent device pixels in the resolution of
 	// the underlying display.
@@ -59,7 +84,7 @@ func (u Unit) String() string {
 }
 
 // Add a list of Values.
-func Add(c Config, values ...Value) Value {
+func Add(c Converter, values ...Value) Value {
 	var sum Value
 	for _, v := range values {
 		sum, v = compatible(c, sum, v)
@@ -69,7 +94,7 @@ func Add(c Config, values ...Value) Value {
 }
 
 // Max returns the maximum of a list of Values.
-func Max(c Config, values ...Value) Value {
+func Max(c Converter, values ...Value) Value {
 	var max Value
 	for _, v := range values {
 		max, v = compatible(c, max, v)
@@ -80,7 +105,7 @@ func Max(c Config, values ...Value) Value {
 	return max
 }
 
-func compatible(c Config, v1, v2 Value) (Value, Value) {
+func compatible(c Converter, v1, v2 Value) (Value, Value) {
 	if v1.U == v2.U {
 		return v1, v2
 	}
diff --git a/widget/image.go b/widget/image.go
index a77e1e3f..8fc7cb38 100644
--- a/widget/image.go
+++ b/widget/image.go
@@ -9,7 +9,7 @@ import (
 	"gioui.org/f32"
 	"gioui.org/layout"
 	"gioui.org/op/paint"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 // Image is a widget that displays an image.
@@ -31,7 +31,7 @@ func (im Image) Layout(gtx *layout.Context) {
 	var w, h int
 	if im.Scale == 0 {
 		const dpPrPx = 160 / 72
-		w, h = gtx.Px(ui.Dp(wf*dpPrPx)), gtx.Px(ui.Dp(hf*dpPrPx))
+		w, h = gtx.Px(unit.Dp(wf*dpPrPx)), gtx.Px(unit.Dp(hf*dpPrPx))
 	} else {
 		w, h = int(wf*im.Scale+.5), int(hf*im.Scale+.5)
 	}