mobile/app/android.go

// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build android

// Go runtime entry point for apps running on android.
// Sets up everything the runtime needs and exposes
// the entry point to JNI.

package app

/*
#cgo LDFLAGS: -llog -landroid

#include <android/log.h>
#include <android/asset_manager.h>
#include <android/configuration.h>
#include <android/native_activity.h>

#include <jni.h>
#include <pthread.h>
#include <stdlib.h>

pthread_cond_t go_started_cond;
pthread_mutex_t go_started_mu;
int go_started;

// current_vm is stored to initialize other cgo packages.
//
// As all the Go packages in a program form a single shared library,
// there can only be one JNI_OnLoad function for iniitialization. In
// OpenJDK there is JNI_GetCreatedJavaVMs, but this is not available
// on android.
JavaVM* current_vm;

// build_auxv builds an ELF auxiliary vector for initializing the Go
// runtime. While there does not appear to be any spec for this
// format, there are some notes in
//
// Phrack, V. 0x0b, Issue 0x3a, P. 0x05.
// http://phrack.org/issues/58/5.html
//
// Much of the time on linux the real auxv can be read from the file
// /proc/self/auxv, however there are several conditions under which
// Android apps cannot read this file (see a note to this effect in
// sources/android/cpufeatures/cpu-features.c). So we construct a
// fake one, working backwards from what the Go runtime wants to see
// as defined by the code in src/runtime/os_linux_GOARCH.c.
void build_auxv(uint32_t *auxv, size_t len);
*/
import "C"
import (
	"fmt"
	"io"
	"log"
	"os"
	"runtime"
	"unsafe"

	"golang.org/x/mobile/geom"
)

var assetManager *C.AAssetManager

//export onCreate
func onCreate(activity *C.ANativeActivity) {
	assetManager = activity.assetManager

	config := C.AConfiguration_new()
	C.AConfiguration_fromAssetManager(config, activity.assetManager)
	density := C.AConfiguration_getDensity(config)
	C.AConfiguration_delete(config)

	var dpi int
	switch density {
	case C.ACONFIGURATION_DENSITY_DEFAULT:
		dpi = 160
	case C.ACONFIGURATION_DENSITY_LOW,
		C.ACONFIGURATION_DENSITY_MEDIUM,
		213, // C.ACONFIGURATION_DENSITY_TV
		C.ACONFIGURATION_DENSITY_HIGH,
		320, // ACONFIGURATION_DENSITY_XHIGH
		480, // ACONFIGURATION_DENSITY_XXHIGH
		640: // ACONFIGURATION_DENSITY_XXXHIGH
		dpi = int(density)
	case C.ACONFIGURATION_DENSITY_NONE:
		log.Print("android device reports no screen density")
		dpi = 72
	default:
		log.Print("android device reports unknown density: %d", density)
		dpi = int(density) // This is a guess.
	}

	geom.PixelsPerPt = float32(dpi) / 72
}

//export onStart
func onStart(activity *C.ANativeActivity) {
}

//export onResume
func onResume(activity *C.ANativeActivity) {
}

//export onSaveInstanceState
func onSaveInstanceState(activity *C.ANativeActivity, outSize *C.size_t) unsafe.Pointer {
	return nil
}

//export onPause
func onPause(activity *C.ANativeActivity) {
}

//export onStop
func onStop(activity *C.ANativeActivity) {
}

//export onDestroy
func onDestroy(activity *C.ANativeActivity) {
}

//export onWindowFocusChanged
func onWindowFocusChanged(activity *C.ANativeActivity, hasFocus int) {
}

//export onNativeWindowCreated
func onNativeWindowCreated(activity *C.ANativeActivity, w *C.ANativeWindow) {
	windowCreated <- w
}

//export onNativeWindowResized
func onNativeWindowResized(activity *C.ANativeActivity, window *C.ANativeWindow) {
}

//export onNativeWindowRedrawNeeded
func onNativeWindowRedrawNeeded(activity *C.ANativeActivity, window *C.ANativeWindow) {
}

//export onNativeWindowDestroyed
func onNativeWindowDestroyed(activity *C.ANativeActivity, window *C.ANativeWindow) {
	windowDestroyed <- true
}

var queue *C.AInputQueue

//export onInputQueueCreated
func onInputQueueCreated(activity *C.ANativeActivity, q *C.AInputQueue) {
	queue = q
}

//export onInputQueueDestroyed
func onInputQueueDestroyed(activity *C.ANativeActivity, queue *C.AInputQueue) {
	queue = nil
}

//export onContentRectChanged
func onContentRectChanged(activity *C.ANativeActivity, rect *C.ARect) {
}

//export onConfigurationChanged
func onConfigurationChanged(activity *C.ANativeActivity) {
}

//export onLowMemory
func onLowMemory(activity *C.ANativeActivity) {
}

// JavaInit is an initialization function registered by the package
// golang.org/x/mobile/bind/java. It gives the Java language
// bindings access to the JNI *JavaVM object.
var JavaInit func(javaVM uintptr)

var (
	windowDestroyed = make(chan bool)
	windowCreated   = make(chan *C.ANativeWindow)
)

func openAsset(name string) (ReadSeekCloser, error) {
	cname := C.CString(name)
	defer C.free(unsafe.Pointer(cname))
	a := &asset{
		ptr:  C.AAssetManager_open(assetManager, cname, C.AASSET_MODE_UNKNOWN),
		name: name,
	}
	if a.ptr == nil {
		return nil, a.errorf("open", "bad asset")
	}
	return a, nil
}

type asset struct {
	ptr  *C.AAsset
	name string
}

func (a *asset) errorf(op string, format string, v ...interface{}) error {
	return &os.PathError{
		Op:   op,
		Path: a.name,
		Err:  fmt.Errorf(format, v...),
	}
}

func (a *asset) Read(p []byte) (n int, err error) {
	n = int(C.AAsset_read(a.ptr, unsafe.Pointer(&p[0]), C.size_t(len(p))))
	if n == 0 && len(p) > 0 {
		return 0, io.EOF
	}
	if n < 0 {
		return 0, a.errorf("read", "negative bytes: %d", n)
	}
	return n, nil
}

func (a *asset) Seek(offset int64, whence int) (int64, error) {
	// TODO(crawshaw): use AAsset_seek64 if it is available.
	off := C.AAsset_seek(a.ptr, C.off_t(offset), C.int(whence))
	if off == -1 {
		return 0, a.errorf("seek", "bad result for offset=%d, whence=%d", offset, whence)
	}
	return int64(off), nil
}

func (a *asset) Close() error {
	C.AAsset_close(a.ptr)
	return nil
}

func run(cb Callbacks) {
	// We want to keep the event loop on a consistent OS thread.
	runtime.LockOSThread()

	ctag := C.CString("Go")
	cstr := C.CString("app.Run")
	C.__android_log_write(C.ANDROID_LOG_INFO, ctag, cstr)
	C.free(unsafe.Pointer(ctag))
	C.free(unsafe.Pointer(cstr))

	if JavaInit != nil {
		JavaInit(uintptr(unsafe.Pointer(C.current_vm)))
	}

	// Inform Java that the program is initialized.
	C.pthread_mutex_lock(&C.go_started_mu)
	C.go_started = 1
	C.pthread_cond_signal(&C.go_started_cond)
	C.pthread_mutex_unlock(&C.go_started_mu)

	for {
		select {
		case w := <-windowCreated:
			windowDrawLoop(cb, w, queue)
		}
	}
}