# Android Go NDK

The Android Go NDK library provides idiomatic Go bindings for the Android NDK, auto-generated from C headers to ensure full coverage and easy maintenance. It wraps 34 NDK modules covering graphics/rendering (EGL, OpenGL ES, Vulkan), camera (Camera2 NDK), audio (AAudio), media codecs, sensors, neural networks (NNAPI), system services (Binder IPC), and more. The bindings feature type-safe APIs with proper resource lifecycle management through `Close()` methods, error handling via the `error` interface, and builder patterns for configuration.

This project is part of a family of three Go libraries covering Android interface surfaces: **ndk** for NDK C API bindings via cgo, **jni** for Java API bindings via JNI+cgo, and **binder** for pure-Go Binder IPC access. The ndk library is ideal for high-performance hardware access including camera, audio, sensors, and OpenGL/Vulkan rendering where low-latency, low-overhead bindings directly to C libraries are essential.

## Audio Package - AAudio Stream Builder

The `audio` package provides Go bindings for Android's AAudio API for low-latency audio playback and recording. The StreamBuilder type configures audio streams with chainable setter methods for sample rate, channel count, format, and performance mode.

```go
package main

import (
	"log"
	"unsafe"

	"github.com/AndroidGoLab/ndk/audio"
)

func main() {
	// Create audio stream builder
	builder, err := audio.NewStreamBuilder()
	if err != nil {
		log.Fatal(err)
	}
	defer builder.Close()

	// Configure stream with chainable methods
	builder.
		SetDirection(audio.Output).
		SetSampleRate(44100).
		SetChannelCount(2).
		SetFormat(audio.PcmFloat).
		SetPerformanceMode(audio.LowLatency).
		SetSharingMode(audio.Shared)

	// Open the configured stream
	stream, err := builder.Open()
	if err != nil {
		log.Fatal(err)
	}
	defer stream.Close()

	log.Printf("opened: %d Hz, %d ch, burst=%d",
		stream.SampleRate(), stream.ChannelCount(), stream.FramesPerBurst())

	// Start playback
	if err := stream.Start(); err != nil {
		log.Fatal(err)
	}
	defer stream.Stop()

	// Write audio data (silence in this example)
	buf := make([]float32, int(stream.FramesPerBurst())*2)
	stream.Write(unsafe.Pointer(&buf[0]), stream.FramesPerBurst(), 1_000_000_000)
}
```

## Audio Package - Microphone Recording

The Stream type supports both playback and recording through direction configuration. Use `audio.Input` direction for microphone capture with PCM format audio data.

```go
package main

import (
	"log"
	"math"
	"time"
	"unsafe"

	"github.com/AndroidGoLab/ndk/audio"
)

func main() {
	builder, err := audio.NewStreamBuilder()
	if err != nil {
		log.Fatalf("create stream builder: %v", err)
	}
	defer builder.Close()

	// Configure for recording
	builder.
		SetDirection(audio.Input).
		SetSampleRate(48000).
		SetChannelCount(1).
		SetFormat(audio.PcmI16).
		SetPerformanceMode(audio.LowLatency).
		SetSharingMode(audio.Shared)

	stream, err := builder.Open()
	if err != nil {
		log.Fatalf("open stream: %v", err)
	}
	defer stream.Close()

	rate := stream.SampleRate()
	log.Printf("capture stream opened (rate=%d Hz, ch=%d)", rate, stream.ChannelCount())

	if err := stream.Start(); err != nil {
		log.Fatalf("start stream: %v", err)
	}

	// Read approximately 1 second of audio
	totalFrames := rate
	buf := make([]int16, 1024)
	bufBytes := unsafe.Slice((*byte)(unsafe.Pointer(&buf[0])), len(buf)*int(unsafe.Sizeof(buf[0])))
	var captured []int16

	for int32(len(captured)) < totalFrames {
		framesToRead := int32(len(buf))
		if remaining := totalFrames - int32(len(captured)); remaining < framesToRead {
			framesToRead = remaining
		}
		n, err := stream.Read(bufBytes, framesToRead, time.Second)
		if err != nil {
			log.Fatalf("read: %v", err)
		}
		captured = append(captured, buf[:n]...)
	}

	if err := stream.Stop(); err != nil {
		log.Fatalf("stop stream: %v", err)
	}

	// Compute peak amplitude
	var peak int16
	for _, s := range captured {
		if s < 0 {
			s = -s
		}
		if s > peak {
			peak = s
		}
	}

	log.Printf("captured %d frames", len(captured))
	log.Printf("peak amplitude: %d (%.1f dBFS)", peak, 20*math.Log10(float64(peak)/32767.0))
}
```

## Camera Package - Manager and Device Discovery

The `camera` package wraps the Android Camera2 NDK API. The Manager type provides camera discovery and device access. All camera operations require the `android.permission.CAMERA` permission.

```go
package main

import (
	"log"

	"github.com/AndroidGoLab/ndk/camera"
)

func main() {
	// Create camera manager - entry point to Camera2 API
	mgr := camera.NewManager()
	defer mgr.Close()

	// List available cameras (requires CAMERA permission)
	ids, err := mgr.CameraIDList()
	if err != nil {
		log.Fatal(err) // camera.ErrPermissionDenied if CAMERA not granted
	}

	for _, id := range ids {
		// Get camera characteristics/metadata
		meta, err := mgr.GetCameraCharacteristics(id)
		if err != nil {
			log.Printf("camera %s: failed to get characteristics: %v", id, err)
			continue
		}

		// Query sensor orientation from metadata
		orientation := meta.I32At(uint32(camera.SensorOrientation), 0)
		log.Printf("camera %s: orientation=%d°", id, orientation)
	}
}
```

## Camera Package - Opening Camera and Capture Session

Opening a camera device requires state callbacks for disconnect/error handling. Create capture requests and sessions to receive camera frames.

```go
package main

import (
	"log"

	"github.com/AndroidGoLab/ndk/camera"
)

func main() {
	mgr := camera.NewManager()
	defer mgr.Close()

	ids, err := mgr.CameraIDList()
	if err != nil || len(ids) == 0 {
		log.Fatal("no cameras available")
	}

	// Open camera with state callbacks
	device, err := mgr.OpenCamera(ids[0], camera.DeviceStateCallbacks{
		OnDisconnected: func() { log.Println("camera disconnected") },
		OnError:        func(code int) { log.Printf("camera error: %d", code) },
	})
	if err != nil {
		log.Fatalf("open camera: %v", err)
	}
	defer device.Close()

	log.Printf("opened camera: %s", device.GetID())

	// Create capture request for preview
	request, err := device.CreateCaptureRequest(camera.Preview)
	if err != nil {
		log.Fatalf("create capture request: %v", err)
	}
	defer request.Close()

	// In a real app, you would:
	// 1. Create OutputTarget from ANativeWindow
	// 2. Add target to request
	// 3. Create SessionOutputContainer
	// 4. Create CaptureSession
	// 5. Set repeating request for continuous preview
}
```

## Sensor Package - Sensor Manager and Queries

The `sensor` package provides access to Android device sensors including accelerometer, gyroscope, light, proximity, and more. Use `GetInstance()` to obtain the singleton SensorManager.

```go
package main

import (
	"fmt"

	"github.com/AndroidGoLab/ndk/sensor"
)

func main() {
	// Get the sensor manager singleton
	mgr := sensor.GetInstance()

	// Query default accelerometer
	accel := mgr.DefaultSensor(sensor.Accelerometer)
	fmt.Printf("Sensor: %s (%s)\n", accel.Name(), accel.Vendor())
	fmt.Printf("Resolution: %g, min delay: %d µs\n",
		accel.Resolution(), accel.MinDelay())

	// Query other sensor types
	sensors := []struct {
		label      string
		sensorType sensor.Type
	}{
		{"Accelerometer", sensor.Accelerometer},
		{"Gyroscope", sensor.Gyroscope},
		{"Light", sensor.Light},
		{"Proximity", sensor.Proximity},
		{"Magnetic Field", sensor.MagneticField},
	}

	fmt.Println("\nDefault sensors on this device:")
	for _, info := range sensors {
		s := mgr.DefaultSensor(info.sensorType)
		if s.UintPtr() == 0 {
			fmt.Printf("  %-16s  not available\n", info.label+":")
			continue
		}
		fmt.Printf("  %s:\n", info.label)
		fmt.Printf("    Name:       %s\n", s.Name())
		fmt.Printf("    Vendor:     %s\n", s.Vendor())
		fmt.Printf("    Type:       %s (%d)\n", info.sensorType, int32(info.sensorType))
		fmt.Printf("    Resolution: %g\n", s.Resolution())
		fmt.Printf("    Min delay:  %d us\n", s.MinDelay())
	}
}
```

## Thermal Package - Device Thermal Status

The `thermal` package monitors device thermal state to adjust workload and prevent throttling. ThermalStatus ranges from None (cool) to Shutdown (critical).

```go
package main

import (
	"fmt"

	"github.com/AndroidGoLab/ndk/thermal"
)

func main() {
	mgr := thermal.NewManager()
	defer mgr.Close()

	status := mgr.CurrentStatus()
	fmt.Printf("Thermal status: %s (%d)\n", status, int32(status))

	switch status {
	case thermal.StatusNone:
		fmt.Println("Device is cool.")
	case thermal.StatusLight, thermal.StatusModerate:
		fmt.Println("Device is warm; consider reducing workload.")
	case thermal.StatusSevere, thermal.StatusCritical:
		fmt.Println("Device is hot; throttling likely.")
	case thermal.StatusEmergency, thermal.StatusShutdown:
		fmt.Println("Device is critically hot; shutdown imminent.")
	default:
		fmt.Println("Unable to determine thermal status.")
	}

	// Get thermal headroom forecast
	headroom := mgr.AThermal_getThermalHeadroom(10) // 10 second forecast
	fmt.Printf("Thermal headroom (10s forecast): %.2f\n", headroom)
}
```

## EGL Package - Display Initialization and Context Creation

The `egl` package wraps the EGL API for creating OpenGL ES rendering contexts. Initialize a display, choose a config, and create surfaces and contexts for rendering.

```go
package main

import (
	"fmt"
	"log"

	"github.com/AndroidGoLab/ndk/egl"
)

func main() {
	// Get the default EGL display
	dpy := egl.GetDisplay(egl.EGLNativeDisplayType(0))
	if dpy == nil {
		log.Fatal("eglGetDisplay failed")
	}

	// Initialize EGL
	var major, minor egl.Int
	if egl.Initialize(dpy, &major, &minor) == egl.False {
		log.Fatalf("eglInitialize failed: 0x%x", egl.GetError())
	}
	defer egl.Terminate(dpy)

	fmt.Printf("EGL %d.%d\n", major, minor)
	fmt.Printf("  Vendor:      %s\n", egl.QueryString(dpy, egl.EGL_VENDOR))
	fmt.Printf("  Version:     %s\n", egl.QueryString(dpy, egl.EGL_VERSION))
	fmt.Printf("  Client APIs: %s\n", egl.QueryString(dpy, egl.EGL_CLIENT_APIS))

	// Choose a config with ES2 support
	attribs := []egl.Int{
		egl.RenderableType, egl.OpenglEs2Bit,
		egl.SurfaceType, egl.PbufferBit,
		egl.RedSize, 8,
		egl.GreenSize, 8,
		egl.BlueSize, 8,
		egl.None,
	}
	var cfg egl.EGLConfig
	var numCfg egl.Int
	if egl.ChooseConfig(dpy, &attribs[0], &cfg, 1, &numCfg) == egl.False || numCfg == 0 {
		log.Fatal("eglChooseConfig failed")
	}

	// Create pbuffer surface and ES2 context
	pbufAttribs := []egl.Int{egl.Width, 1, egl.Height, 1, egl.None}
	surface := egl.CreatePbufferSurface(dpy, cfg, &pbufAttribs[0])

	ctxAttribs := []egl.Int{egl.ContextClientVersion, 2, egl.None}
	ctx := egl.CreateContext(dpy, cfg, nil, &ctxAttribs[0])
	if ctx == nil {
		log.Fatal("eglCreateContext failed")
	}
	defer egl.DestroyContext(dpy, ctx)
	defer egl.DestroySurface(dpy, surface)

	// Make context current
	egl.MakeCurrent(dpy, surface, surface, ctx)
	fmt.Println("EGL context created successfully")

	egl.MakeCurrent(dpy, nil, nil, nil)
}
```

## GLES2 Package - OpenGL ES 2.0 Rendering

The `gles2` package provides OpenGL ES 2.0 bindings for GPU-accelerated rendering. Requires an active EGL context.

```go
package main

import (
	"log"
	"unsafe"

	"github.com/AndroidGoLab/ndk/egl"
	"github.com/AndroidGoLab/ndk/gles2"
)

func goString(p *gles2.GLubyte) string {
	if p == nil {
		return "<nil>"
	}
	var buf []byte
	for ptr := (*byte)(unsafe.Pointer(p)); *ptr != 0; ptr = (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(ptr)) + 1)) {
		buf = append(buf, *ptr)
	}
	return string(buf)
}

func main() {
	// Setup EGL context (abbreviated - see EGL example for full setup)
	dpy := egl.GetDisplay(egl.EGLNativeDisplayType(0))
	var major, minor egl.Int
	egl.Initialize(dpy, &major, &minor)
	defer egl.Terminate(dpy)

	attribs := []egl.Int{egl.RenderableType, egl.OpenglEs2Bit, egl.SurfaceType, egl.PbufferBit, egl.None}
	var cfg egl.EGLConfig
	var numCfg egl.Int
	egl.ChooseConfig(dpy, &attribs[0], &cfg, 1, &numCfg)

	pbuf := []egl.Int{egl.Width, 256, egl.Height, 256, egl.None}
	surface := egl.CreatePbufferSurface(dpy, cfg, &pbuf[0])
	ctxAttribs := []egl.Int{egl.ContextClientVersion, 2, egl.None}
	ctx := egl.CreateContext(dpy, cfg, nil, &ctxAttribs[0])
	defer egl.DestroyContext(dpy, ctx)
	defer egl.DestroySurface(dpy, surface)

	egl.MakeCurrent(dpy, surface, surface, ctx)
	defer egl.MakeCurrent(dpy, nil, nil, nil)

	// Query OpenGL ES info
	log.Printf("GL Vendor:   %s", goString(gles2.GetString(gles2.GL_VENDOR)))
	log.Printf("GL Renderer: %s", goString(gles2.GetString(gles2.GL_RENDERER)))
	log.Printf("GL Version:  %s", goString(gles2.GetString(gles2.GL_VERSION)))

	// Clear screen to red
	gles2.ClearColor(1.0, 0.0, 0.0, 1.0)
	gles2.Clear(gles2.GL_COLOR_BUFFER_BIT)

	// Set viewport
	gles2.Viewport(0, 0, 256, 256)

	// Create and compile shader
	shader := gles2.CreateShader(gles2.GL_VERTEX_SHADER)
	// ... shader source and compilation
	gles2.DeleteShader(shader)

	log.Println("OpenGL ES 2.0 rendering complete")
}
```

## Config Package - Device Configuration

The `config` package queries Android device configuration including screen density, orientation, dimensions, and SDK version.

```go
package main

import (
	"fmt"

	"github.com/AndroidGoLab/ndk/config"
)

func main() {
	cfg := config.NewConfig()
	defer cfg.Close()

	fmt.Println("Device configuration:")
	fmt.Printf("  Density:         %d dpi\n", cfg.Density())
	fmt.Printf("  Orientation:     %d\n", cfg.Orientation())
	fmt.Printf("  Screen size:     %d\n", cfg.ScreenSize())
	fmt.Printf("  Screen width:    %d dp\n", cfg.ScreenWidthDp())
	fmt.Printf("  Screen height:   %d dp\n", cfg.ScreenHeightDp())
	fmt.Printf("  SDK version:     %d\n", cfg.SdkVersion())

	switch config.Orientation(cfg.Orientation()) {
	case config.OrientationPort:
		fmt.Println("  (portrait)")
	case config.OrientationLand:
		fmt.Println("  (landscape)")
	case config.OrientationSquare:
		fmt.Println("  (square)")
	default:
		fmt.Println("  (any/unknown)")
	}
}
```

## Media Package - Codec Creation and Configuration

The `media` package wraps Android's MediaCodec API for hardware-accelerated video and audio encoding/decoding.

```go
package main

import (
	"fmt"

	"github.com/AndroidGoLab/ndk/media"
)

func main() {
	codecs := []struct {
		mime string
		desc string
	}{
		{"video/avc", "H.264 / AVC"},
		{"video/hevc", "H.265 / HEVC"},
		{"video/x-vnd.on2.vp8", "VP8"},
		{"video/x-vnd.on2.vp9", "VP9"},
		{"video/av01", "AV1"},
		{"audio/mp4a-latm", "AAC"},
		{"audio/opus", "Opus"},
		{"audio/flac", "FLAC"},
	}

	fmt.Printf("%-28s %-10s %-10s\n", "MIME Type", "Encoder", "Decoder")
	fmt.Printf("%-28s %-10s %-10s\n", "---", "---", "---")

	for _, c := range codecs {
		encOK := "no"
		enc := media.NewEncoder(c.mime)
		if enc != nil && enc.Pointer() != nil {
			encOK = "yes"
			enc.Close()
		}

		decOK := "no"
		dec := media.NewDecoder(c.mime)
		if dec != nil && dec.Pointer() != nil {
			decOK = "yes"
			dec.Close()
		}

		fmt.Printf("%-28s %-10s %-10s  (%s)\n", c.mime, encOK, decOK, c.desc)
	}
}
```

## Looper Package - Event Loop Management

The `looper` package provides Go bindings for Android's ALooper event loop, used for sensor event queues, input handling, and other async operations.

```go
package main

import (
	"log"
	"runtime"
	"time"
	"unsafe"

	"github.com/AndroidGoLab/ndk/looper"
)

func main() {
	// Lock to OS thread - required for thread-affine APIs
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()

	// Prepare looper for current thread
	lp := looper.Prepare(int32(looper.ALOOPER_PREPARE_ALLOW_NON_CALLBACKS))
	defer lp.Close()

	// Acquire reference to keep looper alive
	lp.Acquire()

	// Wake the looper from another goroutine
	go func() {
		time.Sleep(100 * time.Millisecond)
		lp.Wake()
	}()

	// Poll for events
	var fd, events int32
	var data unsafe.Pointer
	result := looper.LOOPER_POLL(looper.PollOnce(-1, &fd, &events, &data))

	switch result {
	case looper.ALOOPER_POLL_WAKE:
		log.Println("woke up from Wake() call")
	case looper.ALOOPER_POLL_TIMEOUT:
		log.Println("timed out")
	case looper.ALOOPER_POLL_ERROR:
		log.Println("poll error")
	default:
		log.Printf("poll result: %d", result)
	}
}
```

## Asset Package - Loading Bundled Resources

The `asset` package provides access to files bundled in the APK's assets directory through the AssetManager.

```go
package main

import (
	"fmt"
	"io"
	"unsafe"

	"github.com/AndroidGoLab/ndk/asset"
)

func main() {
	// In a real NativeActivity app, obtain manager from activity:
	// mgr := asset.NewManagerFromPointer(activity.AssetManager(nativeActivity))
	var mgr *asset.Manager // = activity.AssetManager(nativeActivity)

	// Open an asset file in streaming mode
	a := mgr.Open("textures/wood.png", asset.Streaming)
	defer a.Close()

	// Get asset size and read contents
	size := a.Length()
	buf := make([]byte, size)
	_, _ = io.ReadFull(unsafe.NewReader(a), buf)
	fmt.Printf("read %d bytes from asset\n", len(buf))

	// Open asset directory
	dir := mgr.OpenDir("textures")
	defer dir.Close()

	// Iterate directory contents
	for {
		name := dir.GetNextFileName()
		if name == "" {
			break
		}
		fmt.Printf("  asset: %s\n", name)
	}
}
```

## Image Package - Image Decoding

The `image` package decodes JPEG, PNG, and other image formats using Android's AImageDecoder API.

```go
package main

import (
	"fmt"
	"log"
	"syscall"
	"unsafe"

	"github.com/AndroidGoLab/ndk/image"
)

func main() {
	// Open image file via POSIX fd
	fd, err := syscall.Open("/sdcard/photo.jpg", syscall.O_RDONLY, 0)
	if err != nil {
		log.Fatalf("open file: %v", err)
	}
	defer syscall.Close(fd)

	// Create decoder from file descriptor
	decoder, err := image.NewDecoderFromFd(int32(fd))
	if err != nil {
		log.Fatalf("create decoder: %v", err)
	}
	defer decoder.Close()

	// Get image dimensions from header
	header := decoder.HeaderInfo()
	// width and height available from header info

	// Get stride and allocate pixel buffer
	stride := decoder.MinimumStride()
	height := int32(480) // example height
	bufSize := stride * uint64(height)
	pixels := make([]byte, bufSize)
	fmt.Printf("Stride: %d bytes, buffer: %d bytes\n", stride, bufSize)

	// Decode image into buffer
	if err := decoder.Decode(unsafe.Pointer(&pixels[0]), stride, bufSize); err != nil {
		log.Fatalf("decode: %v", err)
	}

	// Check if animated (GIF, WebP animation)
	if decoder.IsAnimated() {
		fmt.Println("Image is animated")
		// Use AdvanceFrame() to decode subsequent frames
	}

	fmt.Printf("Decoded %d bytes of pixel data\n", bufSize)
}
```

## Handle Interoperability

All handle types expose `UintPtr()` and `NewXFromUintPtr()` methods for interoperability with other Go packages that use `uintptr` for native handles, including `golang.org/x/mobile`, `gioui.org`, and `github.com/xlab/android-go`.

```go
package main

import (
	"log"

	"github.com/AndroidGoLab/ndk/handle"
	"github.com/AndroidGoLab/ndk/sensor"
)

// All handles implement the NativeHandle interface
func logHandle(h handle.NativeHandle) {
	log.Printf("native handle: 0x%x", h.UintPtr())
}

func main() {
	mgr := sensor.GetInstance()

	// Get handle as uintptr for interop
	ptr := mgr.UintPtr()
	log.Printf("manager uintptr: 0x%x", ptr)

	// Reconstruct from uintptr
	mgr2 := sensor.NewManagerFromUintPtr(ptr)

	// Use with generic interface
	logHandle(mgr2)

	// For gomobile bind (which doesn't support uintptr):
	// Transport as int64 and convert: int64(mgr.UintPtr())
}
```

The Android Go NDK library is designed for Go developers building native Android applications requiring direct access to device hardware and platform services. Primary use cases include real-time audio processing applications using AAudio, camera applications with Camera2 NDK for preview and capture pipelines, sensor-driven applications reading accelerometer/gyroscope/proximity data, and GPU-accelerated rendering with OpenGL ES or Vulkan. The library supports performance-critical applications where the overhead of Java/JNI calls would be prohibitive.

Integration follows standard Go patterns: import the required packages, create manager/builder types, configure with chainable methods, and ensure proper resource cleanup with `defer Close()`. All types implement idempotent, nil-safe Close() methods. Error types wrap NDK status codes and work with `errors.Is()` for error checking. For thread-affine APIs like EGL contexts and ALooper, use `runtime.LockOSThread()`. The library can be combined with the companion `jni` package for Java-only APIs (Bluetooth, WiFi, NFC) and the `binder` package for pure-Go system service access without cgo dependencies.