internal/glfw: Add a new build tag ebitenexternaldll to requrie external DLLs

Embedding a DLL file and extrating it on the fly can be problematic.
The application might be unexpectedly recognized as a virus by some
virus checkers.

To mitigate this issue, Ebiten adds a new build mode `ebitenexternaldll`
which prevents Ebiten from embedding DLL files. Instead, the application
will require DLL files for GLFW.

Closes #1832

doc.go

@@ -78,4 +78,15 @@
 // to manage threads yourself. Functions like IsKeyPressed will no longer be concurrent-safe with this build tag.
 // They must be called from the main thread or the same goroutine as the given game's callback functions like Update
 // to RunGame.
+//
+// `ebitenexternaldll` stops embedding DLL file in a Windows executable.
+// `ebitenexternaldll` works only for Windows.
+// The executable will require a DLL file at the working directory. Copy them from Ebiten repository's `internal/glfw`:
+//
+//   * `glfw_windows_386.dll` for Windows 386
+//   * `glfw_windows_amd64.dll` for Windows amd64
+//
+// Embedding a DLL and extracting it on the fly might be problematic on Windows since the application might be
+// unexpectedly recognized as a virus by some virus checkers.
+// `ebitenexternaldll` is useful for such cases. See #1832 for the discussion.
 package ebiten

internal/glfw/externaldll_windows.go

@@ -0,0 +1,36 @@
+// Copyright 2021 The Ebiten 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.
+
+//go:build ebitenexternaldll
+// +build ebitenexternaldll
+
+package glfw
+
+import (
+	"fmt"
+	"runtime"
+
+	"golang.org/x/sys/windows"
+)
+
+func loadDLL() (*dll, error) {
+	name := "glfw_windows_" + runtime.GOARCH + ".dll"
+	d := windows.NewLazyDLL(name)
+	if err := d.Load(); err != nil {
+		return nil, fmt.Errorf("glfw: failed to load %s: %w", name, err)
+	}
+	return &dll{
+		d: d,
+	}, nil
+}

internal/glfw/gen.go

@@ -127,7 +127,7 @@ func run() error {
 		defer out.Close()
 
 		// As the file name already specified the build environment, buildtags are not requried.
-		if err := file2byteslice.Write(out, in, true, "", "glfw", "glfwDLLCompressed"); err != nil {
+		if err := file2byteslice.Write(out, in, true, "!ebitenexternaldll", "glfw", "glfwDLLCompressed"); err != nil {
 			return err
 		}
 
@@ -141,6 +141,9 @@ func run() error {
 		hashsum := hash.Sum(nil)
 		if _, err := fmt.Fprintf(hashout, `// Code generated by gen.go. DO NOT EDIT.
 
+//go:build !ebitenexternaldll
+// +build !ebitenexternaldll
+
 package glfw
 
 const glfwDLLHash = "%s"
@@ -154,9 +157,6 @@ const glfwDLLHash = "%s"
 				return err
 			}
 		}
-		if err := os.Remove(dll); err != nil {
-			return err
-		}
 	}
 
 	if err := execCommand("gofmt", "-s", "-w", "."); err != nil {

internal/glfw/glfwdllhash_windows_386.go

@@ -1,5 +1,8 @@
 // Code generated by gen.go. DO NOT EDIT.
 
+//go:build !ebitenexternaldll
+// +build !ebitenexternaldll
+
 package glfw
 
 const glfwDLLHash = "9b66cd40f92263367f0076b690cb90174cc981f0c126eb395bc4e35cd8cb767d"

internal/glfw/glfwdllhash_windows_amd64.go

@@ -1,5 +1,8 @@
 // Code generated by gen.go. DO NOT EDIT.
 
+//go:build !ebitenexternaldll
+// +build !ebitenexternaldll
+
 package glfw
 
 const glfwDLLHash = "654e301e14362491530e1c9e2dde434d96eb5c6b11de42af62d85d9cc170f4d8"

internal/glfw/load_windows.go

@@ -15,12 +15,7 @@
 package glfw
 
 import (
-	"bytes"
-	"compress/gzip"
 	"fmt"
-	"io"
-	"os"
-	"path/filepath"
 	"unsafe"
 
 	"golang.org/x/sys/windows"
@@ -43,59 +38,6 @@ func (d *dll) call(name string, args ...uintptr) uintptr {
 	return r
 }
 
-func writeDLLFile(name string) error {
-	f, err := gzip.NewReader(bytes.NewReader(glfwDLLCompressed))
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	out, err := os.Create(name)
-	if err != nil {
-		return err
-	}
-	defer out.Close()
-
-	if _, err := io.Copy(out, f); err != nil {
-		return err
-	}
-	return nil
-}
-
-func loadDLL() (*dll, error) {
-	cachedir, err := os.UserCacheDir()
-	if err != nil {
-		return nil, err
-	}
-
-	dir := filepath.Join(cachedir, "ebiten")
-	if err := os.MkdirAll(dir, 0755); err != nil {
-		return nil, err
-	}
-
-	fn := filepath.Join(dir, glfwDLLHash+".dll")
-	if _, err := os.Stat(fn); err != nil {
-		if !os.IsNotExist(err) {
-			return nil, err
-		}
-
-		// Create a DLL as a temporary file and then rename it later.
-		// Without the temporary file, writing a DLL might fail in the process of writing and Ebiten cannot
-		// notice that the DLL file is incomplete.
-		if err := writeDLLFile(fn + ".tmp"); err != nil {
-			return nil, err
-		}
-
-		if err := os.Rename(fn+".tmp", fn); err != nil {
-			return nil, err
-		}
-	}
-
-	return &dll{
-		d: windows.NewLazyDLL(fn),
-	}, nil
-}
-
 func (d *dll) unload() error {
 	if err := windows.FreeLibrary(windows.Handle(d.d.Handle())); err != nil {
 		return err

internal/glfw/notexternaldll_windows.go

@@ -0,0 +1,81 @@
+// Copyright 2021 The Ebiten 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.
+
+//go:build !ebitenexternaldll
+// +build !ebitenexternaldll
+
+package glfw
+
+import (
+	"bytes"
+	"compress/gzip"
+	"io"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/sys/windows"
+)
+
+func writeDLLFile(name string) error {
+	f, err := gzip.NewReader(bytes.NewReader(glfwDLLCompressed))
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	out, err := os.Create(name)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	if _, err := io.Copy(out, f); err != nil {
+		return err
+	}
+	return nil
+}
+
+func loadDLL() (*dll, error) {
+	cachedir, err := os.UserCacheDir()
+	if err != nil {
+		return nil, err
+	}
+
+	dir := filepath.Join(cachedir, "ebiten")
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return nil, err
+	}
+
+	fn := filepath.Join(dir, glfwDLLHash+".dll")
+	if _, err := os.Stat(fn); err != nil {
+		if !os.IsNotExist(err) {
+			return nil, err
+		}
+
+		// Create a DLL as a temporary file and then rename it later.
+		// Without the temporary file, writing a DLL might fail in the process of writing and Ebiten cannot
+		// notice that the DLL file is incomplete.
+		if err := writeDLLFile(fn + ".tmp"); err != nil {
+			return nil, err
+		}
+
+		if err := os.Rename(fn+".tmp", fn); err != nil {
+			return nil, err
+		}
+	}
+
+	return &dll{
+		d: windows.NewLazyDLL(fn),
+	}, nil
+}