cmd/gogio: add -icon flag for specifying the app icon file

Before users were limited to only use a appicon.png in the root directory.
Now the user is free to use any png anywhere on the system with the help of the -icon flag.

Signed-off-by: Axel Paulander <axel.paulander@gmail.com>

cmd/gogio/androidbuild.go

@@ -350,7 +350,10 @@ func exeAndroid(tmpDir string, tools *androidTools, bi *buildInfo, extraJars, pe
 			return err
 		}
 	}
-	icon := filepath.Join(bi.dir, "appicon.png")
+	icon := *iconPath
+	if icon == "" {
+		icon = filepath.Join(bi.dir, "appicon.png")
+	}
 	iconSnip := ""
 	if _, err := os.Stat(icon); err == nil {
 		err := buildIcons(resDir, icon, []iconVariant{

cmd/gogio/help.go

@@ -15,9 +15,6 @@ programs for platforms where additional metadata or support files are required.
 The package argument specifies an import path or a single Go source file to
 package. Any run arguments are appended to os.Args at runtime.
 
-If the package contains an appicon.png file, it is used as the app icon on
-supported platforms.
-
 Compiled Java class files from jar files in the package directory are
 included in Android builds.
 
@@ -42,6 +39,10 @@ will output an app directory suitable for a simulator.
 The other buildmode is archive, which will output an .aar library for Android
 or a .framework for iOS and tvOS.
 
+The -icon flag specifies a path to a PNG image to use as app icon on iOS and Android.
+If left unspecified, the appicon.png file from the main package is used
+(if it exists).
+
 The -appid flag specifies the package name for Android or the bundle id for
 iOS and tvOS. A bundle id must be provisioned through Xcode before the gogio
 tool can use it.

cmd/gogio/iosbuild.go

@@ -222,7 +222,10 @@ int main(int argc, char * argv[]) {
 	if err := ioutil.WriteFile(plistFile, []byte(infoPlist), 0660); err != nil {
 		return err
 	}
-	icon := filepath.Join(bi.dir, "appicon.png")
+	icon := *iconPath
+	if icon == "" {
+		icon = filepath.Join(bi.dir, "appicon.png")
+	}
 	if _, err := os.Stat(icon); err == nil {
 		assetPlist, err := iosIcons(bi, tmpDir, app, icon)
 		if err != nil {

cmd/gogio/main.go

@@ -34,6 +34,7 @@ var (
 	linkMode      = flag.String("linkmode", "", "set the -linkmode flag of the go tool")
 	extraLdflags  = flag.String("ldflags", "", "extra flags to the Go linker")
 	extraTags     = flag.String("tags", "", "extra tags to the Go tool")
+	iconPath      = flag.String("icon", "", "Specify an icon for iOS and Android")
 )
 
 type buildInfo struct {