Add 'screenshot' feature

If you run your game with environment variable EBITEN_SCREENSHOT_KEY=<keyname>,
you can take a game screenshot by pressing the specified key.

Fixes #553

genkeys.go

@@ -26,6 +26,7 @@ import (
 	"os"
 	"sort"
 	"strconv"
+	"strings"
 	"text/template"
 
 	"github.com/hajimehoshi/ebiten/internal"
@@ -137,6 +138,8 @@ const ebitenKeysTmpl = `{{.License}}
 package ebiten
 
 import (
+	"strings"
+
 	"github.com/hajimehoshi/ebiten/internal/input"
 )
 
@@ -150,6 +153,14 @@ const (
 {{range $index, $name := .KeyNames}}Key{{$name}} Key = Key(input.Key{{$name}})
 {{end}}	KeyMax Key = Key{{.LastKeyName}}
 )
+
+func keyNameToKey(name string) (Key, bool) {
+	switch strings.ToLower(name) {
+	{{range $name := .KeyNames}}case {{$name | printf "%q" | ToLower}}:
+		return Key{{$name}}, true
+	{{end}}}
+	return 0, false
+}
 `
 
 const inputKeysTmpl = `{{.License}}
@@ -332,10 +343,15 @@ func main() {
 			log.Fatal(err)
 		}
 		defer f.Close()
-		tmpl, err := template.New(path).Parse(tmpl)
+
+		funcs := template.FuncMap{
+			"ToLower": strings.ToLower,
+		}
+		tmpl, err := template.New(path).Funcs(funcs).Parse(tmpl)
 		if err != nil {
 			log.Fatal(err)
 		}
+
 		// The build tag can't be included in the templates because of `go vet`.
 		// Pass the build tag and extract this in the template to make `go vet` happy.
 		buildTag := ""

keys.go

@@ -17,6 +17,8 @@
 package ebiten
 
 import (
+	"strings"
+
 	"github.com/hajimehoshi/ebiten/internal/input"
 )
 
@@ -107,3 +109,165 @@ const (
 	KeyUp           Key = Key(input.KeyUp)
 	KeyMax          Key = KeyUp
 )
+
+func keyNameToKey(name string) (Key, bool) {
+	switch strings.ToLower(name) {
+	case "0":
+		return Key0, true
+	case "1":
+		return Key1, true
+	case "2":
+		return Key2, true
+	case "3":
+		return Key3, true
+	case "4":
+		return Key4, true
+	case "5":
+		return Key5, true
+	case "6":
+		return Key6, true
+	case "7":
+		return Key7, true
+	case "8":
+		return Key8, true
+	case "9":
+		return Key9, true
+	case "a":
+		return KeyA, true
+	case "b":
+		return KeyB, true
+	case "c":
+		return KeyC, true
+	case "d":
+		return KeyD, true
+	case "e":
+		return KeyE, true
+	case "f":
+		return KeyF, true
+	case "g":
+		return KeyG, true
+	case "h":
+		return KeyH, true
+	case "i":
+		return KeyI, true
+	case "j":
+		return KeyJ, true
+	case "k":
+		return KeyK, true
+	case "l":
+		return KeyL, true
+	case "m":
+		return KeyM, true
+	case "n":
+		return KeyN, true
+	case "o":
+		return KeyO, true
+	case "p":
+		return KeyP, true
+	case "q":
+		return KeyQ, true
+	case "r":
+		return KeyR, true
+	case "s":
+		return KeyS, true
+	case "t":
+		return KeyT, true
+	case "u":
+		return KeyU, true
+	case "v":
+		return KeyV, true
+	case "w":
+		return KeyW, true
+	case "x":
+		return KeyX, true
+	case "y":
+		return KeyY, true
+	case "z":
+		return KeyZ, true
+	case "alt":
+		return KeyAlt, true
+	case "apostrophe":
+		return KeyApostrophe, true
+	case "backslash":
+		return KeyBackslash, true
+	case "backspace":
+		return KeyBackspace, true
+	case "capslock":
+		return KeyCapsLock, true
+	case "comma":
+		return KeyComma, true
+	case "control":
+		return KeyControl, true
+	case "delete":
+		return KeyDelete, true
+	case "down":
+		return KeyDown, true
+	case "end":
+		return KeyEnd, true
+	case "enter":
+		return KeyEnter, true
+	case "equal":
+		return KeyEqual, true
+	case "escape":
+		return KeyEscape, true
+	case "f1":
+		return KeyF1, true
+	case "f2":
+		return KeyF2, true
+	case "f3":
+		return KeyF3, true
+	case "f4":
+		return KeyF4, true
+	case "f5":
+		return KeyF5, true
+	case "f6":
+		return KeyF6, true
+	case "f7":
+		return KeyF7, true
+	case "f8":
+		return KeyF8, true
+	case "f9":
+		return KeyF9, true
+	case "f10":
+		return KeyF10, true
+	case "f11":
+		return KeyF11, true
+	case "f12":
+		return KeyF12, true
+	case "graveaccent":
+		return KeyGraveAccent, true
+	case "home":
+		return KeyHome, true
+	case "insert":
+		return KeyInsert, true
+	case "left":
+		return KeyLeft, true
+	case "leftbracket":
+		return KeyLeftBracket, true
+	case "minus":
+		return KeyMinus, true
+	case "pagedown":
+		return KeyPageDown, true
+	case "pageup":
+		return KeyPageUp, true
+	case "period":
+		return KeyPeriod, true
+	case "right":
+		return KeyRight, true
+	case "rightbracket":
+		return KeyRightBracket, true
+	case "semicolon":
+		return KeySemicolon, true
+	case "shift":
+		return KeyShift, true
+	case "slash":
+		return KeySlash, true
+	case "space":
+		return KeySpace, true
+	case "tab":
+		return KeyTab, true
+	case "up":
+		return KeyUp, true
+	}
+	return 0, false
+}

run.go

@@ -15,11 +15,14 @@
 package ebiten
 
 import (
+	"fmt"
 	"image"
+	"os"
 	"sync/atomic"
 
 	"github.com/hajimehoshi/ebiten/internal/clock"
 	"github.com/hajimehoshi/ebiten/internal/devicescale"
+	"github.com/hajimehoshi/ebiten/internal/png"
 	"github.com/hajimehoshi/ebiten/internal/ui"
 )
 
@@ -88,6 +91,68 @@ func run(width, height int, scale float64, title string, g *graphicsContext, mai
 	return nil
 }
 
+var screenshot = false
+var screenshotKey Key
+
+func init() {
+	keyname := os.Getenv("EBITEN_SCREENSHOT_KEY")
+	if keyname == "" {
+		return
+	}
+	key, ok := keyNameToKey(keyname)
+	if !ok {
+		return
+	}
+	screenshot = true
+	screenshotKey = key
+}
+
+type screenshotTaker struct {
+	f          func(screen *Image) error
+	keyState   int
+	needToTake bool
+}
+
+func (s *screenshotTaker) update(screen *Image) error {
+	if err := s.f(screen); err != nil {
+		return err
+	}
+	if !screenshot {
+		return nil
+	}
+
+	if IsKeyPressed(screenshotKey) {
+		s.keyState++
+		if s.keyState == 1 {
+			s.needToTake = true
+		}
+	} else {
+		s.keyState = 0
+	}
+	if s.needToTake && !IsRunningSlowly() {
+		filename := "screenshot.png"
+		i := 0
+		for {
+			if _, err := os.Stat(filename); os.IsNotExist(err) {
+				break
+			}
+			i++
+			filename = fmt.Sprintf("screenshot%d.png", i)
+		}
+		f, err := os.Create(filename)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+
+		if err := png.Encode(f, screen); err != nil {
+			return err
+		}
+		s.needToTake = false
+	}
+	return nil
+}
+
 // Run runs the game.
 // f is a function which is called at every frame.
 // The argument (*Image) is the render target that represents the screen.
@@ -118,6 +183,11 @@ func run(width, height int, scale float64, title string, g *graphicsContext, mai
 //
 // Don't call Run twice or more in one process.
 func Run(f func(*Image) error, width, height int, scale float64, title string) error {
+	if screenshot {
+		s := &screenshotTaker{f: f}
+		f = s.update
+	}
+
 	ch := make(chan error)
 	go func() {
 		defer close(ch)
@@ -142,6 +212,11 @@ func Run(f func(*Image) error, width, height int, scale float64, title string) e
 // Ebiten users should NOT call this function.
 // Instead, functions in github.com/hajimehoshi/ebiten/mobile package calls this.
 func RunWithoutMainLoop(f func(*Image) error, width, height int, scale float64, title string) <-chan error {
+	if screenshot {
+		s := &screenshotTaker{f: f}
+		f = s.update
+	}
+
 	ch := make(chan error)
 	go func() {
 		defer close(ch)