From 596e32161041eb3b4b064942a0be5cb728a3793a Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Wed, 17 Jun 2020 11:47:14 +0200
Subject: [PATCH] all: make unit.Converter concrete and rename to Metric

An interface for scaling dp and sp is overkill, at least for all
current uses. Make it a concrete struct type, and rename it to the
shorter and more precise Metric.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 app/internal/window/os_android.go |  6 ++---
 app/internal/window/os_ios.go     |  6 ++---
 app/internal/window/os_js.go      | 13 ++++-----
 app/internal/window/os_macos.go   | 11 ++++----
 app/internal/window/os_wayland.go | 15 ++++++-----
 app/internal/window/os_windows.go | 11 ++++----
 app/internal/window/os_x11.go     |  7 ++---
 app/internal/window/window.go     | 24 -----------------
 gesture/gesture.go                |  2 +-
 internal/fling/animation.go       |  2 +-
 io/system/system.go               |  9 ++-----
 layout/context.go                 | 13 +++------
 layout/list.go                    |  2 +-
 unit/unit.go                      | 44 ++++++++++++++++++++++++++-----
 widget/editor.go                  |  6 ++---
 15 files changed, 86 insertions(+), 85 deletions(-)

diff --git a/app/internal/window/os_android.go b/app/internal/window/os_android.go
index fcce9d98..347c8785 100644
--- a/app/internal/window/os_android.go
+++ b/app/internal/window/os_android.go
@@ -396,9 +396,9 @@ func (w *window) draw(sync bool) {
 				Y: int(height),
 			},
 			Insets: w.insets,
-			Config: &config{
-				pxPerDp: ppdp,
-				pxPerSp: w.fontScale * ppdp,
+			Metric: unit.Metric{
+				PxPerDp: ppdp,
+				PxPerSp: w.fontScale * ppdp,
 			},
 		},
 		Sync: sync,
diff --git a/app/internal/window/os_ios.go b/app/internal/window/os_ios.go
index f63c24c4..10971892 100644
--- a/app/internal/window/os_ios.go
+++ b/app/internal/window/os_ios.go
@@ -119,9 +119,9 @@ func (w *window) draw(sync bool) {
 				Bottom: unit.Px(float32(params.bottom)),
 				Left:   unit.Px(float32(params.left)),
 			},
-			Config: &config{
-				pxPerDp: float32(params.dpi) * inchPrDp,
-				pxPerSp: float32(params.sdpi) * inchPrDp,
+			Metric: unit.Metric{
+				PxPerDp: float32(params.dpi) * inchPrDp,
+				PxPerSp: float32(params.sdpi) * inchPrDp,
 			},
 		},
 		Sync: sync,
diff --git a/app/internal/window/os_js.go b/app/internal/window/os_js.go
index 551a645f..3f383256 100644
--- a/app/internal/window/os_js.go
+++ b/app/internal/window/os_js.go
@@ -15,6 +15,7 @@ import (
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
 	"gioui.org/io/system"
+	"gioui.org/unit"
 )
 
 type window struct {
@@ -407,7 +408,7 @@ func (w *window) ShowTextInput(show bool) {
 
 func (w *window) draw(sync bool) {
 	width, height, scale, cfg := w.config()
-	if cfg == (config{}) || width == 0 || height == 0 {
+	if cfg == (unit.Metric{}) || width == 0 || height == 0 {
 		return
 	}
 	w.mu.Lock()
@@ -420,13 +421,13 @@ func (w *window) draw(sync bool) {
 				X: width,
 				Y: height,
 			},
-			Config: &cfg,
+			Metric: cfg,
 		},
 		Sync: sync,
 	})
 }
 
-func (w *window) config() (int, int, float32, config) {
+func (w *window) config() (int, int, float32, unit.Metric) {
 	rect := w.cnv.Call("getBoundingClientRect")
 	width, height := rect.Get("width").Float(), rect.Get("height").Float()
 	scale := w.window.Get("devicePixelRatio").Float()
@@ -438,9 +439,9 @@ func (w *window) config() (int, int, float32, config) {
 		w.cnv.Set("width", iw)
 		w.cnv.Set("height", ih)
 	}
-	return iw, ih, float32(scale), config{
-		pxPerDp: float32(scale),
-		pxPerSp: float32(scale),
+	return iw, ih, float32(scale), unit.Metric{
+		PxPerDp: float32(scale),
+		PxPerSp: float32(scale),
 	}
 }
 
diff --git a/app/internal/window/os_macos.go b/app/internal/window/os_macos.go
index fef2acda..2378cdb0 100644
--- a/app/internal/window/os_macos.go
+++ b/app/internal/window/os_macos.go
@@ -17,6 +17,7 @@ import (
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
 	"gioui.org/io/system"
+	"gioui.org/unit"
 
 	_ "gioui.org/app/internal/cocoainit"
 )
@@ -236,16 +237,16 @@ func (w *window) draw() {
 				X: width,
 				Y: height,
 			},
-			Config: &cfg,
+			Metric: cfg,
 		},
 		Sync: true,
 	})
 }
 
-func configFor(scale float32) config {
-	return config{
-		pxPerDp: scale,
-		pxPerSp: scale,
+func configFor(scale float32) unit.Metric {
+	return unit.Metric{
+		PxPerDp: scale,
+		PxPerSp: scale,
 	}
 }
 
diff --git a/app/internal/window/os_wayland.go b/app/internal/window/os_wayland.go
index 87209bb6..c85f177f 100644
--- a/app/internal/window/os_wayland.go
+++ b/app/internal/window/os_wayland.go
@@ -25,6 +25,7 @@ import (
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
 	"gioui.org/io/system"
+	"gioui.org/unit"
 	syscall "golang.org/x/sys/unix"
 )
 
@@ -873,7 +874,7 @@ 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()
-	if !w.fling.anim.Start(&c, time.Now(), vel) {
+	if !w.fling.anim.Start(c, time.Now(), vel) {
 		return
 	}
 	invDist := 1 / vel
@@ -1359,11 +1360,11 @@ func (w *window) updateOutputs() {
 	}
 }
 
-func (w *window) config() (int, int, config) {
+func (w *window) config() (int, int, unit.Metric) {
 	width, height := w.width*w.scale, w.height*w.scale
-	return width, height, config{
-		pxPerDp: w.ppdp * float32(w.scale),
-		pxPerSp: w.ppsp * float32(w.scale),
+	return width, height, unit.Metric{
+		PxPerDp: w.ppdp * float32(w.scale),
+		PxPerSp: w.ppsp * float32(w.scale),
 	}
 }
 
@@ -1377,7 +1378,7 @@ func (w *window) draw(sync bool) {
 		return
 	}
 	width, height, cfg := w.config()
-	if cfg == (config{}) {
+	if cfg == (unit.Metric{}) {
 		return
 	}
 	if anim && w.lastFrameCallback == nil {
@@ -1392,7 +1393,7 @@ func (w *window) draw(sync bool) {
 				X: width,
 				Y: height,
 			},
-			Config: &cfg,
+			Metric: cfg,
 		},
 		Sync: sync,
 	})
diff --git a/app/internal/window/os_windows.go b/app/internal/window/os_windows.go
index 41c0d079..1279a155 100644
--- a/app/internal/window/os_windows.go
+++ b/app/internal/window/os_windows.go
@@ -19,6 +19,7 @@ import (
 	syscall "golang.org/x/sys/windows"
 
 	"gioui.org/app/internal/windows"
+	"gioui.org/unit"
 
 	"gioui.org/f32"
 	"gioui.org/io/key"
@@ -377,7 +378,7 @@ func (w *window) draw(sync bool) {
 				X: w.width,
 				Y: w.height,
 			},
-			Config: &cfg,
+			Metric: cfg,
 		},
 		Sync: sync,
 	})
@@ -586,12 +587,12 @@ func convertKeyCode(code uintptr) (string, bool) {
 	return r, true
 }
 
-func configForDC() config {
+func configForDC() unit.Metric {
 	dpi := windows.GetSystemDPI()
 	const inchPrDp = 1.0 / 96.0
 	ppdp := float32(dpi) * inchPrDp
-	return config{
-		pxPerDp: ppdp,
-		pxPerSp: ppdp,
+	return unit.Metric{
+		PxPerDp: ppdp,
+		PxPerSp: ppdp,
 	}
 }
diff --git a/app/internal/window/os_x11.go b/app/internal/window/os_x11.go
index 89bf0646..fdf7d3a3 100644
--- a/app/internal/window/os_x11.go
+++ b/app/internal/window/os_x11.go
@@ -37,6 +37,7 @@ import (
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
 	"gioui.org/io/system"
+	"gioui.org/unit"
 
 	"gioui.org/app/internal/xkb"
 	syscall "golang.org/x/sys/unix"
@@ -64,7 +65,7 @@ type x11Window struct {
 		atom C.Atom
 	}
 	stage  system.Stage
-	cfg    config
+	cfg    unit.Metric
 	width  int
 	height int
 	notify struct {
@@ -193,7 +194,7 @@ loop:
 						X: w.width,
 						Y: w.height,
 					},
-					Config: &w.cfg,
+					Metric: w.cfg,
 				},
 				Sync: syn,
 			})
@@ -474,7 +475,7 @@ func newX11Window(gioWin Callbacks, opts *Options) error {
 	}
 
 	ppsp := x11DetectUIScale(dpy)
-	cfg := config{pxPerDp: ppsp, pxPerSp: ppsp}
+	cfg := unit.Metric{PxPerDp: ppsp, PxPerSp: ppsp}
 	swa := C.XSetWindowAttributes{
 		event_mask: C.ExposureMask | C.FocusChangeMask | // update
 			C.KeyPressMask | C.KeyReleaseMask | // keyboard
diff --git a/app/internal/window/window.go b/app/internal/window/window.go
index d3b30129..f4fa7eca 100644
--- a/app/internal/window/window.go
+++ b/app/internal/window/window.go
@@ -6,7 +6,6 @@ package window
 
 import (
 	"errors"
-	"math"
 
 	"gioui.org/gpu/backend"
 	"gioui.org/io/event"
@@ -71,29 +70,6 @@ type windowAndOptions struct {
 	opts   *Options
 }
 
-// config implements the system.Config interface.
-type config struct {
-	// Device pixels per dp.
-	pxPerDp float32
-	// Device pixels per sp.
-	pxPerSp float32
-}
-
-func (c *config) Px(v unit.Value) int {
-	var r float32
-	switch v.U {
-	case unit.UnitPx:
-		r = v.V
-	case unit.UnitDp:
-		r = c.pxPerDp * v.V
-	case unit.UnitSp:
-		r = c.pxPerSp * v.V
-	default:
-		panic("unknown unit")
-	}
-	return int(math.Round(float64(r)))
-}
-
 func newWindowRendezvous() *windowRendezvous {
 	wr := &windowRendezvous{
 		in:   make(chan windowAndOptions),
diff --git a/gesture/gesture.go b/gesture/gesture.go
index 30d825e3..e13240b7 100644
--- a/gesture/gesture.go
+++ b/gesture/gesture.go
@@ -204,7 +204,7 @@ func (s *Scroll) Stop() {
 
 // Scroll detects the scrolling distance from the available events and
 // ongoing fling gestures.
-func (s *Scroll) Scroll(cfg unit.Converter, q event.Queue, t time.Time, axis Axis) int {
+func (s *Scroll) Scroll(cfg unit.Metric, q event.Queue, t time.Time, axis Axis) int {
 	if s.axis != axis {
 		s.axis = axis
 		return 0
diff --git a/internal/fling/animation.go b/internal/fling/animation.go
index 4a644890..bb6f8a2e 100644
--- a/internal/fling/animation.go
+++ b/internal/fling/animation.go
@@ -31,7 +31,7 @@ const (
 
 // Start a fling given a starting velocity. Returns whether a
 // fling was started.
-func (f *Animation) Start(c unit.Converter, now time.Time, velocity float32) bool {
+func (f *Animation) Start(c unit.Metric, now time.Time, velocity float32) bool {
 	min := float32(c.Px(minFlingVelocity))
 	v := velocity
 	if -min <= v && v <= min {
diff --git a/io/system/system.go b/io/system/system.go
index 4704789e..8abac6d8 100644
--- a/io/system/system.go
+++ b/io/system/system.go
@@ -17,10 +17,11 @@ import (
 // operations that describes what to display and how to handle
 // input.
 type FrameEvent struct {
-	Config Config
 	// Now is the current animation. Use Now instead of time.Now to
 	// synchronize animation and to avoid the time.Now call overhead.
 	Now time.Time
+	// Metric converts device independent dp and sp to device pixels.
+	Metric unit.Metric
 	// Size is the dimensions of the window.
 	Size image.Point
 	// Insets is the insets to apply.
@@ -51,12 +52,6 @@ type FrameEvent struct {
 	Queue event.Queue
 }
 
-// Config defines the essential properties of
-// the environment.
-type Config interface {
-	unit.Converter
-}
-
 // DestroyEvent is the last event sent through
 // a window event channel.
 type DestroyEvent struct {
diff --git a/layout/context.go b/layout/context.go
index 3c5c6393..f47233b8 100644
--- a/layout/context.go
+++ b/layout/context.go
@@ -3,7 +3,6 @@
 package layout
 
 import (
-	"math"
 	"time"
 
 	"gioui.org/io/event"
@@ -20,7 +19,7 @@ type Context struct {
 	// layout.
 	Constraints Constraints
 
-	Config system.Config
+	Metric unit.Metric
 	// By convention, a nil Queue is a signal to widgets to draw themselves
 	// in a disabled state.
 	Queue event.Queue
@@ -47,18 +46,14 @@ func NewContext(ops *op.Ops, e system.FrameEvent) Context {
 		Ops:         ops,
 		Now:         e.Now,
 		Queue:       e.Queue,
-		Config:      e.Config,
+		Metric:      e.Metric,
 		Constraints: Exact(e.Size),
 	}
 }
 
-// Px maps the value to pixels. If no configuration is set,
-// Px returns the rounded value of v.
+// Px maps the value to pixels.
 func (c Context) Px(v unit.Value) int {
-	if c.Config == nil {
-		return int(math.Round(float64(v.V)))
-	}
-	return c.Config.Px(v)
+	return c.Metric.Px(v)
 }
 
 // Events returns the events available for the key. If no
diff --git a/layout/list.go b/layout/list.go
index 689a80ad..b2753cf5 100644
--- a/layout/list.go
+++ b/layout/list.go
@@ -121,7 +121,7 @@ func (l *List) Dragging() bool {
 }
 
 func (l *List) update() {
-	d := l.scroll.Scroll(l.ctx, l.ctx, l.ctx.Now, gesture.Axis(l.Axis))
+	d := l.scroll.Scroll(l.ctx.Metric, l.ctx, l.ctx.Now, gesture.Axis(l.Axis))
 	l.scrollDelta = d
 	l.Position.Offset += d
 }
diff --git a/unit/unit.go b/unit/unit.go
index 05220ae1..fd2245ca 100644
--- a/unit/unit.go
+++ b/unit/unit.go
@@ -22,7 +22,10 @@ values.
 */
 package unit
 
-import "fmt"
+import (
+	"fmt"
+	"math"
+)
 
 // Value is a value with a unit.
 type Value struct {
@@ -33,9 +36,13 @@ 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
+// Metric converts Values to device-dependent pixels, px. The zero
+// value represents a 1-to-1 scale from dp, sp to pixels.
+type Metric struct {
+	// PxPerDp is the device-dependent pixels per dp.
+	PxPerDp float32
+	// PxPerSp is the device-dependent pixels per sp.
+	PxPerSp float32
 }
 
 const (
@@ -90,7 +97,7 @@ func (u Unit) String() string {
 }
 
 // Add a list of Values.
-func Add(c Converter, values ...Value) Value {
+func Add(c Metric, values ...Value) Value {
 	var sum Value
 	for _, v := range values {
 		sum, v = compatible(c, sum, v)
@@ -100,7 +107,7 @@ func Add(c Converter, values ...Value) Value {
 }
 
 // Max returns the maximum of a list of Values.
-func Max(c Converter, values ...Value) Value {
+func Max(c Metric, values ...Value) Value {
 	var max Value
 	for _, v := range values {
 		max, v = compatible(c, max, v)
@@ -111,7 +118,30 @@ func Max(c Converter, values ...Value) Value {
 	return max
 }
 
-func compatible(c Converter, v1, v2 Value) (Value, Value) {
+func (c Metric) Px(v Value) int {
+	var r float32
+	switch v.U {
+	case UnitPx:
+		r = v.V
+	case UnitDp:
+		s := c.PxPerDp
+		if s == 0 {
+			s = 1
+		}
+		r = s * v.V
+	case UnitSp:
+		s := c.PxPerSp
+		if s == 0 {
+			s = 1
+		}
+		r = s * v.V
+	default:
+		panic("unknown unit")
+	}
+	return int(math.Round(float64(r)))
+}
+
+func compatible(c Metric, v1, v2 Value) (Value, Value) {
 	if v1.U == v2.U {
 		return v1, v2
 	}
diff --git a/widget/editor.go b/widget/editor.go
index 2c1b4142..6223ebc9 100644
--- a/widget/editor.go
+++ b/widget/editor.go
@@ -129,7 +129,7 @@ func (e *Editor) processPointer(gtx layout.Context) {
 		axis = gesture.Vertical
 		smin, smax = sbounds.Min.Y, sbounds.Max.Y
 	}
-	sdist := e.scroller.Scroll(gtx, gtx, gtx.Now, axis)
+	sdist := e.scroller.Scroll(gtx.Metric, gtx, gtx.Now, axis)
 	var soff int
 	if e.SingleLine {
 		e.scrollRel(sdist, 0)
@@ -143,7 +143,7 @@ func (e *Editor) processPointer(gtx layout.Context) {
 		case evt.Type == gesture.TypePress && evt.Source == pointer.Mouse,
 			evt.Type == gesture.TypeClick && evt.Source == pointer.Touch:
 			e.blinkStart = gtx.Now
-			e.moveCoord(gtx, image.Point{
+			e.moveCoord(gtx.Metric, image.Point{
 				X: int(math.Round(float64(evt.Position.X))),
 				Y: int(math.Round(float64(evt.Position.Y))),
 			})
@@ -426,7 +426,7 @@ func (e *Editor) scrollAbs(x, y int) {
 	}
 }
 
-func (e *Editor) moveCoord(c unit.Converter, pos image.Point) {
+func (e *Editor) moveCoord(c unit.Metric, pos image.Point) {
 	var (
 		prevDesc fixed.Int26_6
 		carLine  int