app,internal/window: extract native window code to separate package

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/internal/window/window.go

@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// Package window implements platform specific windows
+// and GPU contexts.
+package window
+
+import (
+	"errors"
+	"math"
+	"time"
+
+	"gioui.org/app/internal/gl"
+	"gioui.org/io/event"
+	"gioui.org/io/system"
+	"gioui.org/unit"
+)
+
+type Options struct {
+	Width, Height unit.Value
+	Title         string
+}
+
+type FrameEvent struct {
+	system.FrameEvent
+
+	Sync bool
+}
+
+type Callbacks interface {
+	SetDriver(d Driver)
+	Event(e event.Event)
+}
+
+// Driver is the interface for the platform implementation
+// of a window.
+type Driver interface {
+	// SetAnimating sets the animation flag. When the window is animating,
+	// FrameEvents are delivered as fast as the display can handle them.
+	SetAnimating(anim bool)
+	// ShowTextInput updates the virtual keyboard state.
+	ShowTextInput(show bool)
+	NewContext() (gl.Context, error)
+}
+
+type windowRendezvous struct {
+	in   chan windowAndOptions
+	out  chan windowAndOptions
+	errs chan error
+}
+
+type windowAndOptions struct {
+	window Callbacks
+	opts   *Options
+}
+
+// config implements the system.Config interface.
+type config struct {
+	// Device pixels per dp.
+	pxPerDp float32
+	// Device pixels per sp.
+	pxPerSp float32
+	now     time.Time
+}
+
+func (c *config) Now() time.Time {
+	return c.now
+}
+
+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),
+		out:  make(chan windowAndOptions),
+		errs: make(chan error),
+	}
+	go func() {
+		var main windowAndOptions
+		var out chan windowAndOptions
+		for {
+			select {
+			case w := <-wr.in:
+				var err error
+				if main.window != nil {
+					err = errors.New("multiple windows are not supported")
+				}
+				wr.errs <- err
+				main = w
+				out = wr.out
+			case out <- main:
+			}
+		}
+	}()
+	return wr
+}
+
+const (
+	inchPrDp = 1.0 / 160
+	mmPrDp   = 25.4 / 160
+	// monitorScale is the extra scale applied to
+	// monitor outputs to compensate for the extra
+	// viewing distance compared to phone and tables.
+	monitorScale = 1.20
+	// minDensity is the minimum pixels per dp to
+	// ensure font and ui legibility on low-dpi
+	// screens.
+	minDensity = 1.25
+)