From e5b95691427be1e897939832a3fd84630793b9f5 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Thu, 29 Dec 2022 15:44:18 +0900
Subject: [PATCH] internal/ui: bug fix: the env variable should be used only
 when the library is not specified

Updates #2378
---
 doc.go                  |  2 +-
 internal/ui/graphics.go | 39 ++++++++++++++++++++-------------------
 2 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/doc.go b/doc.go
index d33815118..d61e9418f 100644
--- a/doc.go
+++ b/doc.go
@@ -67,7 +67,7 @@
 //
 // `EBITENGINE_GRAPHICS_LIBRARY` environment variable specifies the graphics library.
 // If the specified graphics library is not available, RunGame returns an error.
-// This environment variable can also be set programmatically through os.Setenv before RunGame is called.
+// This environment variable works when RunGame is called or RunGameWithOptions is called with GraphicsLibraryAuto.
 // This can take one of the following value:
 //
 //	"auto":    Ebitengine chooses the graphics library automatically. This is the default value.
diff --git a/internal/ui/graphics.go b/internal/ui/graphics.go
index a87c5a608..932e25a7b 100644
--- a/internal/ui/graphics.go
+++ b/internal/ui/graphics.go
@@ -29,26 +29,27 @@ type graphicsDriverCreator interface {
 }
 
 func newGraphicsDriver(creator graphicsDriverCreator, graphicsLibrary GraphicsLibrary) (graphicsdriver.Graphics, error) {
-	envName := "EBITENGINE_GRAPHICS_LIBRARY"
-	env := os.Getenv(envName)
-	if env == "" {
-		// For backward compatibility, read the EBITEN_ version.
-		envName = "EBITEN_GRAPHICS_LIBRARY"
-		env = os.Getenv(envName)
-	}
+	if graphicsLibrary == GraphicsLibraryAuto {
+		envName := "EBITENGINE_GRAPHICS_LIBRARY"
+		env := os.Getenv(envName)
+		if env == "" {
+			// For backward compatibility, read the EBITEN_ version.
+			envName = "EBITEN_GRAPHICS_LIBRARY"
+			env = os.Getenv(envName)
+		}
 
-	switch env {
-	case "", "auto":
-		// Use the specified graphics library.
-		// Otherwise, prefer the environment variable.
-	case "opengl":
-		graphicsLibrary = GraphicsLibraryOpenGL
-	case "directx":
-		graphicsLibrary = GraphicsLibraryDirectX
-	case "metal":
-		graphicsLibrary = GraphicsLibraryMetal
-	default:
-		return nil, fmt.Errorf("ui: an unsupported graphics library is specified by the environment variable: %s", env)
+		switch env {
+		case "", "auto":
+			// Keep the automatic choosing.
+		case "opengl":
+			graphicsLibrary = GraphicsLibraryOpenGL
+		case "directx":
+			graphicsLibrary = GraphicsLibraryDirectX
+		case "metal":
+			graphicsLibrary = GraphicsLibraryMetal
+		default:
+			return nil, fmt.Errorf("ui: an unsupported graphics library is specified by the environment variable: %s", env)
+		}
 	}
 
 	switch graphicsLibrary {