Change APIs to return errors

example/blocks/game.go

@@ -54,7 +54,7 @@ func (game *Game) isInitialized() bool {
 
 var once sync.Once
 
-func (game *Game) Update() {
+func (game *Game) Update() error {
 	once.Do(func() {
 		for name, path := range texturePaths {
 			game.textures.RequestTexture(name, path)
@@ -64,18 +64,20 @@ func (game *Game) Update() {
 		}
 	})
 	if !game.isInitialized() {
-		return
+		return nil
 	}
 	game.input.Update()
 	game.sceneManager.Update(&GameState{
 		SceneManager: game.sceneManager,
 		Input:        game.input,
 	})
+	return nil
 }
 
-func (game *Game) Draw(context graphics.Context) {
+func (game *Game) Draw(context graphics.Context) error {
 	if !game.isInitialized() {
-		return
+		return nil
 	}
 	game.sceneManager.Draw(context, game.textures)
+	return nil
 }

graphics/context.go

@@ -18,16 +18,10 @@ type TexturePart struct {
 }
 
 type Drawer interface {
-	Draw(parts []TexturePart,
-		geometryMatrix matrix.Geometry,
-		colorMatrix matrix.Color)
+	Draw(parts []TexturePart, geometryMatrix matrix.Geometry, colorMatrix matrix.Color)
 }
 
-func DrawWhole(
-	drawer Drawer,
-	width, height int,
-	geo matrix.Geometry,
-	color matrix.Color) {
+func DrawWhole(drawer Drawer, width, height int, geo matrix.Geometry, color matrix.Color) {
 	parts := []TexturePart{
 		{0, 0, Rect{0, 0, width, height}},
 	}

graphics/opengl/context.go

@@ -4,6 +4,7 @@ import (
 	"github.com/go-gl/gl"
 	"github.com/hajimehoshi/ebiten/graphics"
 	"github.com/hajimehoshi/ebiten/graphics/matrix"
+	"github.com/hajimehoshi/ebiten/ui"
 	"sync"
 )
 
@@ -59,11 +60,13 @@ func (c *Context) Dispose() {
 }
 
 // TODO: This interface is confusing: Can we change this?
-func (c *Context) Update(draw func(graphics.Context)) {
+func (c *Context) Update(drawer ui.Drawer) error {
 	c.ResetOffscreen()
 	c.Clear()
 
-	draw(c)
+	if err := drawer.Draw(c); err != nil {
+		return err
+	}
 
 	c.SetOffscreen(c.defaultId)
 	c.Clear()
@@ -74,6 +77,7 @@ func (c *Context) Update(draw func(graphics.Context)) {
 	graphics.DrawWhole(c.RenderTarget(c.screenId), c.screenWidth, c.screenHeight, geo, matrix.ColorI())
 
 	flush()
+	return nil
 }
 
 func (c *Context) Clear() {

ui/glfw/canvas.go

@@ -43,11 +43,12 @@ func NewCanvas(width, height, scale int, title string) *Canvas {
 	return canvas
 }
 
-func (c *Canvas) Draw(f func(graphics.Context)) {
+func (c *Canvas) Draw(d ui.Drawer) (err error) {
 	c.use(func() {
-		c.context.Update(f)
+		err = c.context.Update(d)
 		c.window.SwapBuffers()
 	})
+	return
 }
 
 func (c *Canvas) IsClosed() bool {

ui/glfw/ui.go

@@ -1,6 +1,7 @@
 package glfw
 
 import (
+	"errors"
 	glfw "github.com/go-gl/glfw3"
 	"github.com/hajimehoshi/ebiten/ui"
 	"log"
@@ -16,13 +17,14 @@ type UI struct {
 	canvas *Canvas
 }
 
-func (u *UI) Start(width, height, scale int, title string) ui.Canvas {
+func (u *UI) Start(width, height, scale int, title string) (ui.Canvas, error) {
 	if !glfw.Init() {
-		panic("glfw.Init() fails")
+		// TODO: Use glfw error
+		return nil, errors.New("glfw.Init() fails")
 	}
 	glfw.WindowHint(glfw.Resizable, glfw.False)
 	u.canvas = NewCanvas(width, height, scale, title)
-	return u.canvas
+	return u.canvas, nil
 }
 
 func (u *UI) DoEvents() {

ui/run.go

@@ -9,12 +9,15 @@ import (
 )
 
 type Game interface {
-	Draw(context graphics.Context)
-	Update()
+	Update() error
+	Draw(context graphics.Context) error
 }
 
-func Run(u UI, game Game, width, height, scale int, title string, fps int) {
-	canvas := u.Start(width, height, scale, title)
+func Run(u UI, game Game, width, height, scale int, title string, fps int) error {
+	canvas, err := u.Start(width, height, scale, title)
+	if err != nil {
+		return err
+	}
 
 	frameTime := time.Duration(int64(time.Second) / int64(fps))
 	tick := time.Tick(frameTime)
@@ -26,14 +29,18 @@ func Run(u UI, game Game, width, height, scale int, title string, fps int) {
 		u.DoEvents()
 		select {
 		default:
-			canvas.Draw(game.Draw)
+			if err := canvas.Draw(game); err != nil {
+				return err
+			}
 		case <-tick:
-			game.Update()
+			if err := game.Update(); err != nil {
+				return err
+			}
 			if canvas.IsClosed() {
-				return
+				return nil
 			}
 		case <-sigterm:
-			return
+			return nil
 		}
 	}
 }

ui/ui.go

@@ -5,12 +5,16 @@ import (
 )
 
 type UI interface {
-	Start(widht, height, scale int, title string) Canvas
+	Start(widht, height, scale int, title string) (Canvas, error)
 	DoEvents()
 	Terminate()
 }
 
+type Drawer interface {
+	Draw(c graphics.Context) error
+}
+
 type Canvas interface {
-	Draw(func(graphics.Context))
+	Draw(drawer Drawer) error
 	IsClosed() bool
 }