The document outlines the architecture of the Android camera system, focusing on design patterns such as Proxy and Singleton. It details the implementation of these patterns within the camera service and the process of accessing the camera service via a Binder interface. Key code snippets illustrate how methods like setting the preview display are executed within the camera framework.

1. Android Camera Architecture Author: Picker

2. Architecture

4. Architecture Path of the Source Code frameworks/base/core/java/android/hardware/ frameworks/base/core/jni/ frameworks/base/libs/camera/ frameworks/base/services/camera/libcameraservice/ vendor/nvidia/tegra/hal/libnvomxcamera/

5. Proxy Pattern

6. Reference to: Design Patterns by Gamma, Helm, Johnson, Vlissides

7. A Possible Object Diagram of Proxy Structure at Run-Time Proxy Structure Reference to: Design Patterns by Gamma, Helm, Johnson, Vlissides

8. Implementation - Design a Abstract Class for Proxy and Server to Extend it. - Give an RealObject Instance for Proxy. Execute these Methods by Proxy. - The Client just Need to Face the Proxy.

9. Singleton Pattern

10. Reference to: Design Patterns by Gamma, Helm, Johnson, Vlissides Singleton Structure

11. Reference to: Design Patterns by Gamma, Helm, Johnson, Vlissides Singleton* Singleton::_instance = 0; Singleton* Singleton::Instance () { if (_instance == 0) { _instance = new Singleton; } return _instance; } Implementation

12. Architecture Diagram

13. Proxy Pattern Singleton Pattern

14. 33 // client singleton for camera service binder interface 34 Mutex Camera::mLock; 35 sp<ICameraService> Camera::mCameraService; 36 sp<Camera::DeathNotifier> Camera::mDeathNotifier; Singleton Pattern Camera.cpp frameworks/base/libs/camera/

15. 38 // establish binder interface to camera service 39 const sp<ICameraService>& Camera::getCameraService() 40 { 41 Mutex::Autolock _l(mLock); 42 if (mCameraService.get() == 0) { 43 sp<IServiceManager> sm = defaultServiceManager(); 44 sp<IBinder> binder; 45 do { 46 binder = sm->getService(String16(&quot;media.camera&quot;)); 47 if (binder != 0) 48 break; 49 LOGW(&quot;CameraService not published, waiting...&quot;); 50 usleep(500000); // 0.5 s 51 } while(true); 52 if (mDeathNotifier == NULL) { 53 mDeathNotifier = new DeathNotifier(); 54 } 55 binder->linkToDeath(mDeathNotifier); 56 mCameraService = interface_cast<ICameraService>(binder); 57 } 58 LOGE_IF(mCameraService==0, &quot;no CameraService!?&quot;); 59 return mCameraService; 60 } Camera.cpp frameworks/base/libs/camera/

16. 53 class BpCamera: public BpInterface<ICamera> 54 { 55 public: 56 BpCamera(const sp<IBinder>& impl) 57 : BpInterface<ICamera>(impl) 58 { 59 } 60 61 // disconnect from camera service 62 void disconnect() 63 { 64 LOGV(&quot;disconnect&quot;); 65 Parcel data, reply; 66 data.writeInterfaceToken(ICamera::getInterfaceDescriptor()); 67 remote()->transact(DISCONNECT, data, &reply); 68 } ICamera.cpp frameworks/base/libs/camera/ Proxy Pattern - Sender

17. 34 class CameraService : 35 public BinderService<CameraService>, 36 public BnCameraService 37 { 38 class Client; 39 friend class BinderService<CameraService>; 82 class Client : public BnCamera 83 { 84 public: 85 // ICamera interface (see ICamera for details) 86 virtual void disconnect(); 87 virtual status_t connect(const sp<ICameraClient>& client); 88 virtual status_t lock(); 89 virtual status_t unlock(); … … … 206 } Proxy Pattern - Receiver CameraService.h frameworks/base/services/camera/libcameraservice/

18. A Simple Workflow of Starting the Camera Preview

20. An Example: Set the Preview Display

21. 349 public final void setPreviewDisplay (SurfaceHolder holder) throws IOException { 350 if (holder != null) { 351 setPreviewDisplay (holder.getSurface()); 352 } else { 353 setPreviewDisplay ((Surface)null); 354 } 355 } Camera.java frameworks/base/core/java/android/hardware/

22. android_hardware_Camera.cpp 381 static void android_hardware_Camera_setPreviewDisplay ( JNIEnv *env, jobject thiz, jobject jSurface) 382 { 383 LOGV(&quot;setPreviewDisplay&quot;); 384 sp<Camera> camera = get_native_camera(env, thiz, NULL); 385 if (camera == 0) return; 386 387 sp<Surface> surface = NULL; 388 if (jSurface != NULL) { 389 surface = reinterpret_cast<Surface*>( env->GetIntField(jSurface, fields.surface)); 390 } 391 if ( camera->setPreviewDisplay (surface) != NO_ERROR) { 392 jniThrowException(env, &quot;java/io/IOException&quot;, &quot;setPreviewDisplay failed&quot;); 393 } 394 } frameworks/base/core/jni/

23. Camera.cpp frameworks/base/libs/camera/ 171 // pass the buffered ISurface to the camera service 172 status_t Camera::setPreviewDisplay (const sp<Surface>& surface) 173 { 174 LOGV(&quot;setPreviewDisplay&quot;); 175 sp <ICamera> c = mCamera; 176 if (c == 0) return NO_INIT; 177 if (surface != 0) { 178 return c->setPreviewDisplay (surface->getISurface()); 179 } else { 180 LOGD(&quot;app passed NULL surface&quot;); 181 return c->setPreviewDisplay (0); 182 } 183 }

24. ICamera.cpp 70 // pass the buffered ISurface to the camera service 71 status_t setPreviewDisplay (const sp<ISurface>& surface) 72 { 73 LOGV(&quot;setPreviewDisplay&quot;); 74 Parcel data, reply; 75 data.writeInterfaceToken(ICamera::getInterfaceDescriptor()); 76 data.writeStrongBinder(surface->asBinder()); 77 remote()->transact (SET_PREVIEW_DISPLAY, data, &reply); 78 return reply.readInt32(); 79 } frameworks/base/libs/camera/

25. CameraService.cpp frameworks/base/libs/camera/ 485 status_t CameraService::Client::setPreviewDisplay (const sp<ISurface>& surface) { 486 LOG1(&quot;setPreviewDisplay(%p) (pid %d)&quot;, surface.get(), getCallingPid()); … … … 510 mSurface = surface; 511 mOverlayRef = 0; 512 // If preview has been already started, set overlay or register preview 513 // buffers now. 514 if ( mHardware->previewEnabled() ) { 515 if (mUseOverlay) { 516 result = setOverlay(); 517 } else if (mSurface != 0) { 518 result = registerPreviewBuffers(); 519 } 520 }

26. frameworks/base/libs/camera/ CameraService.cpp 525 status_t CameraService::Client::registerPreviewBuffers () { 526 int w, h; 527 CameraParameters params(mHardware->getParameters()); 528 params.getPreviewSize(&w, &h); 529 530 // FIXME: don't use a hardcoded format here. 531 ISurface::BufferHeap buffers(w, h, w, h, 532 HAL_PIXEL_FORMAT_YCrCb_420_SP, 533 mOrientation, 534 0, 535 mHardware->getPreviewHeap ()); 536 537 status_t result = mSurface->registerBuffers(buffers); 538 if (result != NO_ERROR) { 539 LOGE(&quot;registerBuffers failed with status %d&quot;, result); 540 } 541 return result; 542 }

27. frameworks/base/libs/camera/ CameraHardwareStub.cpp 104 sp<IMemoryHeap> CameraHardwareStub::getPreviewHeap() const 105 { 106 return mPreviewHeap; 107 }