From dad071293c66be5a9a3a240fc54e0cc1312d0b48 Mon Sep 17 00:00:00 2001
From: Greg <gmp@wow.st>
Date: Fri, 18 Oct 2019 14:40:35 -0400
Subject: [PATCH] Add JNI example.

---
 README.md                                     |  15 ++
 examples/jni/AClass.java                      |   9 ++
 examples/jni/jni_android.go                   | 130 ++++++++++++++++++
 examples/jni/main.go                          |  80 +++++++++++
 examples/jni/os_android.go                    |  39 ++++++
 examples/jni/os_other.go                      |   7 +
 examples/sensors/main.go                      |  46 +++----
 .../sensors/{android.go => os_android.go}     |   4 -
 go.mod                                        |   2 +-
 go.sum                                        |  24 ++++
 10 files changed, 322 insertions(+), 34 deletions(-)
 create mode 100644 examples/jni/AClass.java
 create mode 100644 examples/jni/jni_android.go
 create mode 100644 examples/jni/main.go
 create mode 100644 examples/jni/os_android.go
 create mode 100644 examples/jni/os_other.go
 rename examples/sensors/{android.go => os_android.go} (98%)

diff --git a/README.md b/README.md
index 76783c2..38c8fe1 100644
--- a/README.md
+++ b/README.md
@@ -10,3 +10,18 @@ cd $GOPATH/src/git.wow.st/gmp/android-go/examples/sensors
 gogio -target android -minsdk 27 .
 adb install -r sensors.apk
 ```
+
+There is also an example showing how to incorporate custom Java classes
+and access them (and the rest of the Android system) via JNI. To build it
+(on a Unix-like environment):
+
+```
+go get git.wow.st/gmp/android-go/examples/jni
+cd $GOPATH/src/git.wow.st/gmp/android-go/examples/jni
+go generate os_android.go
+gogio -target android -minsdk 27 .
+adb install -r jni.apk
+```
+
+To build on Windows, you will need to re-write the `go:generate` commands
+at the top of `os_android.go` as appropriate.
diff --git a/examples/jni/AClass.java b/examples/jni/AClass.java
new file mode 100644
index 0000000..632e657
--- /dev/null
+++ b/examples/jni/AClass.java
@@ -0,0 +1,9 @@
+package st.wow.git.jni;
+
+public class AClass {
+	public int Num() {
+		return 17;
+	}
+}
+
+
diff --git a/examples/jni/jni_android.go b/examples/jni/jni_android.go
new file mode 100644
index 0000000..e078ee1
--- /dev/null
+++ b/examples/jni/jni_android.go
@@ -0,0 +1,130 @@
+package main
+
+/*
+#cgo LDFLAGS: -landroid
+
+#include <stdlib.h>
+#include <jni.h>
+#include <android/log.h>
+
+static jobject gClassLoader;
+static jmethodID gFindClassMethod;
+
+void
+SetLoader(JNIEnv* env, jobject context) {
+	jclass cclass = (*env)->GetObjectClass(env, context);
+	jmethodID gcl_id = (*env)->GetMethodID(env, cclass, "getClassLoader", "()Ljava/lang/ClassLoader;");
+	jobject loader = (*env)->CallObjectMethod(env, context, gcl_id);
+	gClassLoader = (*env)->NewGlobalRef(env, loader);
+	jclass lclass = (*env)->GetObjectClass(env, loader);
+	gFindClassMethod = (*env)->GetMethodID(env, lclass, "findClass", "(Ljava/lang/String;)Ljava/lang/Class;");
+}
+
+jclass
+FindClass(JNIEnv* env, char* name) {
+	jstring strClassName = (*env)->NewStringUTF(env, name);
+	return (*env)->CallObjectMethod(env, gClassLoader, gFindClassMethod, strClassName);
+}
+
+JNIEXPORT jobject
+CreateObject(JNIEnv* env, jclass cls) {
+	jmethodID init = (*env)->GetMethodID(env, cls, "<init>", "()V");
+	return (*env)->NewObject(env, cls, init);
+}
+
+void CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
+	(*env)->CallVoidMethod(env, obj, methodID);
+}
+
+jint CallIntMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
+	return (*env)->CallIntMethod(env, obj, methodID);
+}
+
+jmethodID GetMethodID(JNIEnv *env, jclass clazz, const char *name, const char *sig) {
+	return (*env)->GetMethodID(env, clazz, name, sig);
+}
+
+jint GetEnv(JavaVM *vm, JNIEnv **env, jint version) {
+	return (*vm)->GetEnv(vm, (void **)env, version);
+}
+
+jint AttachCurrentThread(JavaVM *vm, JNIEnv **p_env, void *thr_args) {
+	return (*vm)->AttachCurrentThread(vm, p_env, thr_args);
+}
+
+jint DetachCurrentThread(JavaVM *vm) {
+	return (*vm)->DetachCurrentThread(vm);
+}
+
+*/
+import "C"
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"runtime"
+	"unsafe"
+)
+
+var theJVM *C.JavaVM
+type JNIEnv = C.JNIEnv
+
+func SetJVM(jvm, context uintptr) {
+	log.Print("set theJVM")
+	theJVM = (*C.JavaVM)(unsafe.Pointer(jvm))
+	log.Printf("theJVM = %d", uintptr(unsafe.Pointer(theJVM)))
+	RunInJVM(func(env *C.JNIEnv) {
+		C.SetLoader(env, (C.jobject)(context))
+	})
+}
+
+func FindClass(env *C.JNIEnv, name string) C.jclass {
+	cname := C.CString(name)
+	defer C.free(unsafe.Pointer(cname))
+	return C.FindClass((*C.JNIEnv)(env), cname)
+}
+
+func JniCallVoidMethod(env *C.JNIEnv, obj C.jobject, methodID C.jmethodID) {
+	C.CallVoidMethod(env, obj, methodID)
+}
+
+func JniCallIntMethod(env *C.JNIEnv, obj C.jobject, methodID C.jmethodID) int {
+	return (int)(C.CallIntMethod(env, obj, methodID))
+}
+
+func JniGetMethodID(env *C.JNIEnv, cls C.jclass, name, sig string) C.jmethodID {
+	cname := C.CString(name)
+	defer C.free(unsafe.Pointer(cname))
+	csig := C.CString(sig)
+	defer C.free(unsafe.Pointer(csig))
+	return C.GetMethodID(env, cls, cname, csig)
+}
+
+func CreateObject(env *C.JNIEnv, cls C.jclass) C.jobject {
+	return C.CreateObject(env, (C.jclass)(cls))
+}
+
+func RunInJVM(f func(env *C.JNIEnv)) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	var env *C.JNIEnv
+	var detach bool
+	log.Printf("RunInJVM(): theJVM = %d", uintptr(unsafe.Pointer(theJVM)))
+	if res := C.GetEnv(theJVM, &env, C.JNI_VERSION_1_6); res != C.JNI_OK {
+		if res != C.JNI_EDETACHED {
+			panic(fmt.Errorf("JNI GetEnv failed with error %d", res))
+		}
+		if C.AttachCurrentThread(theJVM, &env, nil) != C.JNI_OK {
+			panic(errors.New("runInJVM: AttachCurrentThread failed"))
+		}
+		detach = true
+	}
+
+	if detach {
+		defer func() {
+			C.DetachCurrentThread(theJVM)
+		}()
+	}
+	f(env)
+}
diff --git a/examples/jni/main.go b/examples/jni/main.go
new file mode 100644
index 0000000..c5e8977
--- /dev/null
+++ b/examples/jni/main.go
@@ -0,0 +1,80 @@
+// +build darwin linux
+
+package main
+
+import (
+	"log"
+
+	"gioui.org/app"
+	"gioui.org/io/system"
+	"gioui.org/layout"
+	"gioui.org/unit"
+	"gioui.org/widget/material"
+
+	_ "gioui.org/font/gofont"
+)
+
+var (
+	labchan chan string
+)
+
+func main() {
+	labchan = make(chan string)
+	log.Print("Staring event loop")
+	go eventloop()
+	app.Main()
+	log.Print("app.Main() returned")
+}
+
+func diffInsets(x, y system.Insets) bool {
+	return x.Top != y.Top ||
+		x.Bottom != y.Bottom ||
+		x.Left != y.Left ||
+		x.Right != y.Right
+}
+
+func eventloop() {
+	w := app.NewWindow(
+		app.Size(unit.Dp(400), unit.Dp(400)),
+		app.Title("Hello"))
+	th := material.NewTheme()
+	gtx := &layout.Context{Queue: w.Queue()}
+
+	sysinset := &layout.Inset{}
+	margin := layout.UniformInset(unit.Dp(10))
+	labels := []material.Label{}
+	list := &layout.List{Axis: layout.Vertical}
+
+	resetSysinset := func(x system.Insets) {
+		sysinset.Top = x.Top
+		sysinset.Bottom = x.Bottom
+		sysinset.Left = x.Left
+		sysinset.Right = x.Right
+	}
+	go func() {
+		labchan <- "Starting"
+		callJni()
+	}()
+	for {
+		select {
+		case x := <-labchan:
+			labels = append(labels, th.Body1(x))
+		case e := <-w.Events():
+			switch e := e.(type) {
+			case system.DestroyEvent:
+				return
+			case system.FrameEvent:
+				gtx.Reset(e.Config, e.Size)
+				resetSysinset(e.Insets)
+				sysinset.Layout(gtx, func() {
+					margin.Layout(gtx, func() {
+						list.Layout(gtx, len(labels), func(i int) {
+							labels[i].Layout(gtx)
+						})
+					})
+				})
+				e.Frame(gtx.Ops)
+			}
+		}
+	}
+}
diff --git a/examples/jni/os_android.go b/examples/jni/os_android.go
new file mode 100644
index 0000000..609e381
--- /dev/null
+++ b/examples/jni/os_android.go
@@ -0,0 +1,39 @@
+//go:generate javac -bootclasspath $ANDROID_HOME/platforms/android-29/android.jar AClass.java
+//go:generate jar cf AClass.jar AClass.class
+//go:generate rm AClass.class
+
+package main
+
+import (
+	"fmt"
+	"log"
+	"time"
+
+	"gioui.org/app"
+)
+
+func callJni() {
+	time.Sleep(time.Second/5)
+	h := app.PlatformHandle()
+	labchan <- fmt.Sprintf("JVM = %d", h.JVM)
+	labchan <- fmt.Sprintf("Context = %d", h.Context)
+	SetJVM(h.JVM, h.Context)
+
+	RunInJVM(func(env *JNIEnv) {
+		log.Print("finding class")
+		cls := FindClass(env, "st/wow/git/jni/AClass")
+		log.Print("getting methodID")
+		mth := JniGetMethodID(env, cls, "Num", "()I")
+		if mth == nil {
+			labchan <- "nil method"
+			return
+		}
+		log.Print("creating object")
+		inst := CreateObject(env, cls)
+		log.Print("calling method")
+		val := JniCallIntMethod(env, inst, mth)
+		log.Print("got result")
+		labchan <- fmt.Sprintf("val = %d", val)
+	})
+}
+
diff --git a/examples/jni/os_other.go b/examples/jni/os_other.go
new file mode 100644
index 0000000..2f6fa48
--- /dev/null
+++ b/examples/jni/os_other.go
@@ -0,0 +1,7 @@
+// +build !android
+
+package main
+
+func callJni() {
+}
+
diff --git a/examples/sensors/main.go b/examples/sensors/main.go
index 0148850..12e4650 100644
--- a/examples/sensors/main.go
+++ b/examples/sensors/main.go
@@ -3,25 +3,18 @@
 package main
 
 import (
-	"image/color"
 	"log"
 
 	"gioui.org/app"
+	"gioui.org/io/system"
 	"gioui.org/layout"
-	"gioui.org/text"
-	"gioui.org/text/shape"
 	"gioui.org/unit"
+	"gioui.org/widget/material"
 
-	"golang.org/x/image/font/gofont/goregular"
-	"golang.org/x/image/font/sfnt"
+	_ "gioui.org/font/gofont"
 )
 
 var (
-	face  text.Face
-	white = color.RGBA{A: 0xff, R: 0xff, G: 0xff, B: 0xff}
-	gray  = color.RGBA{A: 0xff, R: 0xb0, G: 0xb0, B: 0xb0}
-	black = color.RGBA{A: 0xff, R: 0x00, G: 0x00, B: 0x00}
-
 	labchan chan string
 )
 
@@ -33,7 +26,7 @@ func main() {
 	log.Print("App closed")
 }
 
-func diffInsets(x, y app.Insets) bool {
+func diffInsets(x, y system.Insets) bool {
 	return x.Top != y.Top ||
 		x.Bottom != y.Bottom ||
 		x.Left != y.Left ||
@@ -42,41 +35,36 @@ func diffInsets(x, y app.Insets) bool {
 
 func eventloop() {
 	w := app.NewWindow(
-		app.WithWidth(unit.Dp(400)),
-		app.WithHeight(unit.Dp(400)),
-		app.WithTitle("Hello"))
+		app.Size(unit.Dp(400), unit.Dp(400)),
+		app.Title("Hello"))
+	th := material.NewTheme()
 	gtx := &layout.Context{Queue: w.Queue()}
-	var faces shape.Faces
-
-	regular, err := sfnt.Parse(goregular.TTF)
-	if err != nil {
-		log.Fatal("Cannot parse font.")
-	}
-	face = faces.For(regular, unit.Sp(16))
 
 	sysinset := &layout.Inset{}
 	margin := layout.UniformInset(unit.Dp(10))
-	labels := []*text.Label{}
+	labels := []material.Label{}
 	list := &layout.List{Axis: layout.Vertical}
 
-	resetSysinset := func(x app.Insets) {
+	resetSysinset := func(x system.Insets) {
 		sysinset.Top = x.Top
 		sysinset.Bottom = x.Bottom
 		sysinset.Left = x.Left
 		sysinset.Right = x.Right
 	}
 
+	go func() {
+		labchan <- "Starting"
+	}()
 	for {
 		select {
 		case x := <-labchan:
-			labels = append(labels, &text.Label{Face: face, Text: x})
+			labels = append(labels, th.Body1(x))
 		case e := <-w.Events():
 			switch e := e.(type) {
-			case app.DestroyEvent:
+			case system.DestroyEvent:
 				return
-			case app.UpdateEvent:
-				gtx.Reset(&e.Config, e.Size)
-				faces.Reset(&e.Config)
+			case system.FrameEvent:
+				gtx.Reset(e.Config, e.Size)
 				resetSysinset(e.Insets)
 				sysinset.Layout(gtx, func() {
 					margin.Layout(gtx, func() {
@@ -85,7 +73,7 @@ func eventloop() {
 						})
 					})
 				})
-				w.Update(gtx.Ops)
+				e.Frame(gtx.Ops)
 			}
 		}
 	}
diff --git a/examples/sensors/android.go b/examples/sensors/os_android.go
similarity index 98%
rename from examples/sensors/android.go
rename to examples/sensors/os_android.go
index 8373723..9c56fdb 100644
--- a/examples/sensors/android.go
+++ b/examples/sensors/os_android.go
@@ -1,9 +1,5 @@
-//+build android
-
 package main
 
-import "C"
-
 import (
 	"fmt"
 	"log"
diff --git a/go.mod b/go.mod
index 1c62467..0c15508 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,6 @@ module git.wow.st/gmp/android-go
 go 1.13
 
 require (
-	gioui.org v0.0.0-20191003113651-f3819d816490
+	gioui.org v0.0.0-20191018181617-5ef176af8145
 	golang.org/x/image v0.0.0-20190910094157-69e4b8554b2a
 )
diff --git a/go.sum b/go.sum
index b9f0437..de1c8a3 100644
--- a/go.sum
+++ b/go.sum
@@ -1,9 +1,33 @@
+dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
 gioui.org v0.0.0-20191003113651-f3819d816490 h1:gEVjHOvnfHdfOiPCTMQuwFp5iceBK/i8QcVd44F1ejs=
 gioui.org v0.0.0-20191003113651-f3819d816490/go.mod h1:+CEjc9B//HrBfWsQOVxjCyih7HGIj3Pww1xFHVDZyyk=
+gioui.org v0.0.0-20191018144543-175144fa99b5 h1:gLTisL9HKeXoYbSXXEe6SRhy1K+FsZEyUmlnxCzIQoE=
+gioui.org v0.0.0-20191018144543-175144fa99b5/go.mod h1:KqFFi2Dq5gYA3FJ0sDOt8OBXoMsuxMtE8v2f0JExXAY=
+gioui.org v0.0.0-20191018181617-5ef176af8145 h1:7zU3Wky5H9jKAhHLsc4Zbs5uDcIh3WmW4HdnPhz997A=
+gioui.org v0.0.0-20191018181617-5ef176af8145/go.mod h1:KqFFi2Dq5gYA3FJ0sDOt8OBXoMsuxMtE8v2f0JExXAY=
+github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
+github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
+golang.org/x/exp v0.0.0-20191002040644-a1355ae1e2c3 h1:n9HxLrNxWWtEb1cA950nuEEj3QnKbtsCJ6KjcgisNUs=
+golang.org/x/exp v0.0.0-20191002040644-a1355ae1e2c3/go.mod h1:NOZ3BPKG0ec/BKJQgnvsSFpcKLM5xXVWnvZS97DWHgE=
+golang.org/x/image v0.0.0-20190227222117-0694c2d4d067/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
 golang.org/x/image v0.0.0-20190703141733-d6a02ce849c9/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
+golang.org/x/image v0.0.0-20190802002840-cff245a6509b/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/image v0.0.0-20190910094157-69e4b8554b2a h1:gHevYm0pO4QUbwy8Dmdr01R5r1BuKtfYqRqF0h/Cbh0=
 golang.org/x/image v0.0.0-20190910094157-69e4b8554b2a/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
+golang.org/x/mobile v0.0.0-20190719004257-d2bd2a29d028/go.mod h1:E/iHnbuqvinMTCcRqshq8CkpyQDoeVncDDYHnLhea+o=
+golang.org/x/mod v0.1.0/go.mod h1:0QHyrYULN0/3qlju5TqG8bIK38QM8yzMo5ekMj3DlcY=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
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 golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a h1:aYOabOQFp6Vj6W1F80affTUvO9UxmJRx8K0gsfABByQ=
 golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20190927191325-030b2cf1153e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=