ui/app: call main from Android and iOS

Android can only run c-shared libraries which means that every
Gio program must create its window and event loop from an init
function.

The same applies to iOS but for a more benign reason: the gio tool
builds programs in c-archive mode for iOS and links the binary with
a Objective-C driver.

Allow Gio programs to run off its main function by linking to and
invoking main even from Android libraries and iOS ditto.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

apps/go.mod

@@ -3,7 +3,7 @@ module gioui.org/apps
 go 1.12
 
 require (
-	gioui.org/ui v0.0.0-20190721195854-dd081c78b96d
+	gioui.org/ui v0.0.0-20190721200230-1ee8c08f3bf9
 	github.com/google/go-github/v24 v24.0.1
 	golang.org/x/exp v0.0.0-20190627132806-fd42eb6b336f
 	golang.org/x/image v0.0.0-20190703141733-d6a02ce849c9

cmd/gio/iosbuild.go

@@ -139,10 +139,13 @@ func exeIOS(tmpDir, target, app string, bi *buildInfo) error {
 	const mainmSrc = `@import UIKit;
 @import Gio;
 
+void gio_runMain(void);
+
 int main(int argc, char * argv[]) {
-    @autoreleasepool {
-        return UIApplicationMain(argc, argv, nil, NSStringFromClass([GioAppDelegate class]));
-    }
+	@autoreleasepool {
+		gio_runMain();
+		return UIApplicationMain(argc, argv, nil, NSStringFromClass([GioAppDelegate class]));
+	}
 }`
 	if err := ioutil.WriteFile(mainm, []byte(mainmSrc), 0660); err != nil {
 		return err

ui/app/GioView.java

@@ -27,7 +27,6 @@ import java.io.UnsupportedEncodingException;
 public class GioView extends SurfaceView implements Choreographer.FrameCallback {
 	private final static Object initLock = new Object();
 	private static boolean jniLoaded;
-	private static String dataDir;
 
 	private final SurfaceHolder.Callback callbacks;
 	private final InputMethodManager imm;
@@ -39,20 +38,19 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 			if (jniLoaded) {
 				return;
 			}
-			dataDir = appCtx.getFilesDir().getAbsolutePath();
+			String dataDir = appCtx.getFilesDir().getAbsolutePath();
+			byte[] dataDirUTF8;
+			try {
+				dataDirUTF8 = dataDir.getBytes("UTF-8");
+			} catch (UnsupportedEncodingException e) {
+				throw new RuntimeException(e);
+			}
 			System.loadLibrary("gio");
+			runGoMain(dataDirUTF8);
 			jniLoaded = true;
 		}
 	}
 
-	static byte[] dataDir() {
-		try {
-			return dataDir.getBytes("UTF-8");
-		} catch (UnsupportedEncodingException e) {
-			throw new RuntimeException(e);
-		}
-	}
-
 	public GioView(Context context) {
 		this(context, null);
 	}
@@ -221,6 +219,7 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 	static private native void onFrameCallback(long handle, long nanos);
 	static private native boolean onBack(long handle);
 	static private native void onFocusChange(long handle, boolean focus);
+	static private native void runGoMain(byte[] dataDir);
 
 	private static class InputConnection extends BaseInputConnection {
 		private final Editable editable;

ui/app/datadir_android.go

@@ -20,8 +20,6 @@ func dataDir() (string, error) {
 	return dataPath, nil
 }
 
-//export setDataDir
-func setDataDir(cdir *C.char, len C.int) {
-	dir := C.GoStringN(cdir, len)
+func setDataDir(dir string) {
 	dataDirChan <- dir
 }

ui/app/gl_ios.go

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-//+build darwin,ios
+// +build darwin,ios
 
 package app
 

ui/app/gl_ios.m

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-//+build darwin,ios
+// +build darwin,ios
 
 @import UIKit;
 @import OpenGLES;

ui/app/gl_macos.m

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-//+build darwin,!ios
+// +build darwin,!ios
 
 @import AppKit;
 

ui/app/os_android.c

@@ -1,6 +1,8 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
 #include <jni.h>
+#include <dlfcn.h>
+#include <android/log.h>
 #include "os_android.h"
 #include "_cgo_export.h"
 
@@ -18,6 +20,11 @@ JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
 	}
 
 	static const JNINativeMethod methods[] = {
+		{
+			.name = "runGoMain",
+			.signature = "([B)V",
+			.fnPtr = runGoMain
+		},
 		{
 			.name = "onCreateView",
 			.signature = "(Lorg/gioui/GioView;)J",
@@ -93,23 +100,6 @@ JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
 		return -1;
 	}
 
-	// Initialize data dir.
-	jmethodID dataDirMethod = (*env)->GetStaticMethodID(env, viewClass, "dataDir", "()[B");
-	if (dataDirMethod == NULL) {
-		return -1;
-	}
-	jbyteArray dirArr = (*env)->CallStaticObjectMethod(env, viewClass, dataDirMethod);
-	if (dirArr == NULL) {
-		return -1;
-	}
-	jbyte *dir = (*env)->GetByteArrayElements(env, dirArr, NULL);
-	if (dir == NULL) {
-		return -1;
-	}
-	jint n = (*env)->GetArrayLength(env, dirArr);
-	setDataDir((char *)dir, n);
-	(*env)->ReleaseByteArrayElements(env, dirArr, dir, JNI_ABORT);
-
 	return JNI_VERSION_1_6;
 }
 
@@ -164,3 +154,15 @@ void gio_jni_CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
 void gio_jni_CallVoidMethod_J(JNIEnv *env, jobject obj, jmethodID methodID, jlong a1) {
 	(*env)->CallVoidMethod(env, obj, methodID, a1);
 }
+
+jbyte *gio_jni_GetByteArrayElements(JNIEnv *env, jbyteArray arr) {
+	return (*env)->GetByteArrayElements(env, arr, NULL);
+}
+
+void gio_jni_ReleaseByteArrayElements(JNIEnv *env, jbyteArray arr, jbyte *bytes) {
+	(*env)->ReleaseByteArrayElements(env, arr, bytes, JNI_ABORT);
+}
+
+jsize gio_jni_GetArrayLength(JNIEnv *env, jbyteArray arr) {
+	return (*env)->GetArrayLength(env, arr);
+}

ui/app/os_android.go

@@ -76,6 +76,19 @@ func jniGetStaticMethodID(env *C.JNIEnv, class C.jclass, method, sig string) C.j
 	return C.gio_jni_GetStaticMethodID(env, class, m, s)
 }
 
+//export runGoMain
+func runGoMain(env *C.JNIEnv, class C.jclass, jdataDir C.jbyteArray) {
+	dirBytes := C.gio_jni_GetByteArrayElements(env, jdataDir)
+	if dirBytes == nil {
+		panic("runGoMain: GetByteArrayElements failed")
+	}
+	n := C.gio_jni_GetArrayLength(env, jdataDir)
+	dataDir := C.GoStringN((*C.char)(unsafe.Pointer(dirBytes)), n)
+	setDataDir(dataDir)
+	C.gio_jni_ReleaseByteArrayElements(env, jdataDir, dirBytes)
+	runMain()
+}
+
 //export setJVM
 func setJVM(vm *C.JavaVM) {
 	theJVM = vm
@@ -407,8 +420,6 @@ func (w *window) showTextInput(show bool) {
 }
 
 func Main() {
-	// Android runs in c-shared mode where main is never reached.
-	panic("call to Main from outside main")
 }
 
 func createWindow(window *Window, opts *WindowOptions) error {

ui/app/os_android.h

@@ -14,3 +14,6 @@ __attribute__ ((visibility ("hidden"))) jfloat gio_jni_CallFloatMethod(JNIEnv *e
 __attribute__ ((visibility ("hidden"))) jint gio_jni_CallIntMethod(JNIEnv *env, jobject obj, jmethodID methodID);
 __attribute__ ((visibility ("hidden"))) void gio_jni_CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID);
 __attribute__ ((visibility ("hidden"))) void gio_jni_CallVoidMethod_J(JNIEnv *env, jobject obj, jmethodID methodID, jlong a1);
+__attribute__ ((visibility ("hidden"))) jbyte *gio_jni_GetByteArrayElements(JNIEnv *env, jbyteArray arr);
+__attribute__ ((visibility ("hidden"))) void gio_jni_ReleaseByteArrayElements(JNIEnv *env, jbyteArray arr, jbyte *bytes);
+__attribute__ ((visibility ("hidden"))) jsize gio_jni_GetArrayLength(JNIEnv *env, jbyteArray arr);

ui/app/os_ios.go

@@ -252,6 +252,4 @@ func createWindow(win *Window, opts *WindowOptions) error {
 }
 
 func Main() {
-	// iOS runs in c-archive mode, so this is never reached.
-	panic("call to Main from outside main")
 }

ui/app/runmain.go

@@ -0,0 +1,22 @@
+// +build android darwin,ios
+
+package app
+
+// Android only supports non-Java programs as c-shared libraries.
+// Unfortunately, Go does not run a program's main function in
+// library mode. To make Gio programs simpler and uniform, we'll
+// link to the main function here and call it from Java.
+
+import _ "unsafe" // for go:linkname
+
+//go:linkname mainMain main.main
+func mainMain()
+
+func runMain() {
+	go func() {
+		// Indirect call, since the linker does not know the address of main when
+		// laying down this package.
+		fn := mainMain
+		fn()
+	}()
+}

ui/app/runmain_ios.go

@@ -0,0 +1,10 @@
+// +build darwin,ios
+
+package app
+
+import "C"
+
+//export gio_runMain
+func gio_runMain() {
+	runMain()
+}