ebiten: add APIs to treat monitors (#2597)

This change adds these APIs:

* `type MonitorType`
* `func (*MonitorType) Bounds() image.Rectangle`
* `func (*MonitorType) Name() string`
* `func Monitor() *MonitorType`
* `func SetMonitor(*MonitorType)`
* `func AppendMonitors([]*MonitorType) []*MonitorType`

Closes #1835

examples/monitor/main.go

@@ -0,0 +1,127 @@
+// Copyright 2023 The Ebitengine Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"image/color"
+	"log"
+
+	"golang.org/x/image/font"
+	"golang.org/x/image/font/opentype"
+
+	"github.com/hajimehoshi/ebiten/v2"
+	"github.com/hajimehoshi/ebiten/v2/examples/resources/fonts"
+	"github.com/hajimehoshi/ebiten/v2/inpututil"
+	"github.com/hajimehoshi/ebiten/v2/text"
+)
+
+var (
+	mplusNormalFont font.Face
+)
+
+func init() {
+	tt, err := opentype.Parse(fonts.MPlus1pRegular_ttf)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	const dpi = 72
+	mplusNormalFont, err = opentype.NewFace(tt, &opentype.FaceOptions{
+		Size:    24,
+		DPI:     dpi,
+		Hinting: font.HintingFull,
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+const (
+	screenWidth  = 640
+	screenHeight = 480
+)
+
+type Game struct {
+	monitors []*ebiten.MonitorType
+}
+
+func (g *Game) Update() error {
+	// Refresh monitors.
+	g.monitors = ebiten.AppendMonitors(g.monitors[:0])
+
+	// Handle keypresses.
+	if inpututil.IsKeyJustReleased(ebiten.KeyF) {
+		ebiten.SetFullscreen(!ebiten.IsFullscreen())
+	} else {
+		for i, m := range g.monitors {
+			if inpututil.IsKeyJustPressed(ebiten.KeyDigit0 + ebiten.Key(i)) {
+				ebiten.SetWindowTitle(m.Name())
+				ebiten.SetMonitor(m)
+			}
+		}
+	}
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	const x = 0
+	y := 24
+	text.Draw(screen, "F to toggle fullscreen\n0-9 to change monitor", mplusNormalFont, x, y, color.White)
+	y += 72
+
+	for i, m := range g.monitors {
+		text.Draw(screen, fmt.Sprintf("%d: %s %s", i, m.Name(), m.Bounds().String()), mplusNormalFont, x, y, color.White)
+		y += 24
+	}
+
+	activeMonitor := ebiten.Monitor()
+	for i, m := range g.monitors {
+		if m == activeMonitor {
+			text.Draw(screen, fmt.Sprintf("active: %s (%d)", m.Name(), i), mplusNormalFont, x, y, color.White)
+		}
+	}
+}
+
+func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
+	return screenWidth, screenHeight
+}
+
+func main() {
+	g := &Game{}
+
+	// Allow the user to pass in a monitor flag to target a specific monitor.
+	var monitor int
+	flag.IntVar(&monitor, "monitor", 0, "target monitor index to run the program on")
+	flag.Parse()
+
+	// Read our monitors.
+	g.monitors = ebiten.AppendMonitors(nil)
+
+	// Ensure the user did not supply a monitor index beyond the range of available monitors. If they did, set the monitor to the primary.
+	if monitor < 0 || monitor >= len(g.monitors) {
+		monitor = 0
+	}
+
+	targetMonitor := g.monitors[monitor]
+	ebiten.SetMonitor(targetMonitor)
+	ebiten.SetWindowTitle(targetMonitor.Name())
+	ebiten.SetWindowSize(screenWidth, screenHeight)
+
+	if err := ebiten.RunGame(g); err != nil {
+		log.Fatal(err)
+	}
+}