From 81e0e61a430a42b5a255f2a84c5be83efcda5776 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Mon, 4 Dec 2023 01:16:39 +0900
Subject: [PATCH] text/v2: let NewMultiFace return an error

Updates #2845
---
 examples/mixedfont/main.go |  6 +++++-
 text/v2/multi.go           | 18 ++++++++++++++++--
 text/v2/text_test.go       |  5 ++++-
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/examples/mixedfont/main.go b/examples/mixedfont/main.go
index d54c3e9c0..27f2cd878 100644
--- a/examples/mixedfont/main.go
+++ b/examples/mixedfont/main.go
@@ -74,7 +74,11 @@ func (g *Game) Update() error {
 			Size:   32,
 		}
 
-		g.face = text.NewMultiFace(en, ja)
+		f, err := text.NewMultiFace(en, ja)
+		if err != nil {
+			return err
+		}
+		g.face = f
 	}
 	return nil
 }
diff --git a/text/v2/multi.go b/text/v2/multi.go
index 8797255f4..8eadbeb7a 100644
--- a/text/v2/multi.go
+++ b/text/v2/multi.go
@@ -15,6 +15,7 @@
 package text
 
 import (
+	"errors"
 	"unicode/utf8"
 
 	"github.com/hajimehoshi/ebiten/v2/vector"
@@ -31,11 +32,24 @@ type MultiFace struct {
 }
 
 // NewMultiFace creates a new MultiFace from the given faces.
-func NewMultiFace(faces ...Face) *MultiFace {
+//
+// NewMultiFace returns an error when no faces are given, or the faces' directions don't agree.
+func NewMultiFace(faces ...Face) (*MultiFace, error) {
+	if len(faces) == 0 {
+		return nil, errors.New("text: no faces are given at NewMultiFace")
+	}
+
+	d := faces[0].direction()
+	for _, f := range faces[1:] {
+		if f.direction() != d {
+			return nil, errors.New("text: all the faces' directions must agree")
+		}
+	}
+
 	m := &MultiFace{}
 	m.faces = make([]Face, len(faces))
 	copy(m.faces, faces)
-	return m
+	return m, nil
 }
 
 // Metrics implements Face.
diff --git a/text/v2/text_test.go b/text/v2/text_test.go
index a76051d27..01e123d62 100644
--- a/text/v2/text_test.go
+++ b/text/v2/text_test.go
@@ -243,7 +243,10 @@ func TestUnhashableFace(t *testing.T) {
 
 func TestMultiFace(t *testing.T) {
 	faces := []text.Face{text.NewStdFace(bitmapfont.Face)}
-	f := text.NewMultiFace(faces...)
+	f, err := text.NewMultiFace(faces...)
+	if err != nil {
+		t.Fatal(err)
+	}
 	img := ebiten.NewImage(30, 30)
 	text.Draw(img, "Hello", f, nil)