【Android Camera1】Android Camera1综述

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简介：

本篇文章是Camera1概览。

• Camera1的源码细节可参看Camera系列文章之Camera1源码。
• 具体可运行的代码可参看Camera系列文章之Camera1开源项目分析
• 具体完善的开发细节和问题处理可参看Camera系列文章之Camera1初始化，AF，AE，常见问题等文章。

Camera1简介

目前Android提供3个Camera框架，Camera1、Camera2、CameraX；Camera1作为最早期框架再API level1就已经存在，随着Android SDK的升级，在Level21推荐使用Camera2代替Camera1; 但在实际的应用开发中，考虑到诸多兼容性问题，仍然会把Camera1作为兜底的一种Camera功能实现方式。

相比较Camera2、CameraX。Camera1更像是一个黑盒，提供基本的相机功能：如

• 预览
• 视频录制
• 静态拍摄

Camera1衡量维度

要想使用Camera1开发一个健壮性比较高的应用，还需要多多实践，以结果说话。具体可从如下维度衡量

• 相机初始化的稳定性
• 相机拍照的稳定性
• 相机录制视频的稳定性
• 相机的初始化和拍照性能
• 相机拍出照片的质量等等

Camera系列文章也会始终以这些衡量维度去阐述具体的细节处理。

Camera.java

相比较Camera2和CameraX来说，Camera1的Java层源码十分简单，一个类Camera.java 囊括了App开发中使用的所有相关代码。当然具体的实现功能还是Native层面。

Camera HAL1

相机的功能实现在Native层，向上提供应用接口，Camera框架之间的差异也代表了HAL之间的差异。

HAL 位于相机驱动程序和更高级别的 Android 框架之间，它定义您必须实现的接口，以便应用可以正确地操作相机硬件。

HAL 可定义一个标准接口以供硬件供应商实现，可让Android忽略较低级别的驱动程序实现。HAL实现通常会内置在共享库模块(.so)中。

Camera1的HAL架构图可以参考左侧部分。可以看到从上到下涉及到的类不是很复杂。

简单可抽象为如下流程，由于Camera1是向后兼容的，所以之后的Android SDK都可以使用Camera1来实现自己App相关的相机Feature。

宏观流程

Camera1整体的理论知识可参考如下网站和资料

• 官方文档说明
• 官方API文档

接下来分为如下几个部分来介绍，详细的细节可参考Camera系列文章里Camera1源码文章：

1. 基本配置
2. 使用相机功能流程
3. 自定义开发相机功能流程

基本配置

AndroidManifest.xml

uses-permission

• android.permission.CAMERA
• android.permission.WRITE_EXTERNAL_STORAGE
• android.permission.RECORD_AUDIO

基本上涉及到相机，存储和录音3个权限，在App启动时需要向用户申请通过相关权限，否则将无法执行后续流程。

uses-feature

• android:name="android.hardware.camera" android:required="true"
• android.hardware.camera.autofocus
• android.hardware.camera.any
• android.hardware.camera.flash

对应App的相关能力特征

使用

通过发送相应的intent可使用相应的三方相机能力，具体的模版代码可参考官方文档。这里简单列一下关键的intent 和其说明。需要特别注意的是代码里面列出来的异常，在使用之前一定要保证最基本的前提条件：权限申请，Android SDK版本兼容等。
android.media.action.IMAGE_CAPTURE

   /*** Standard Intent action that can be sent to have the camera application* capture an image and return it.* <p>* The caller may pass an extra EXTRA_OUTPUT to control where this image will be written.* If the EXTRA_OUTPUT is not present, then a small sized image is returned as a Bitmap* object in the extra field. This is useful for applications that only need a small image.* If the EXTRA_OUTPUT is present, then the full-sized image will be written to the Uri* value of EXTRA_OUTPUT.* As of {@link android.os.Build.VERSION_CODES#LOLLIPOP}, this uri can also be supplied through* {@link android.content.Intent#setClipData(ClipData)}. If using this approach, you still must* supply the uri through the EXTRA_OUTPUT field for compatibility with old applications.* If you don't set a ClipData, it will be copied there for you when calling* {@link Context#startActivity(Intent)}.** <p>Note: if you app targets {@link android.os.Build.VERSION_CODES#M M} and above* and declares as using the {@link android.Manifest.permission#CAMERA} permission which* is not granted, then attempting to use this action will result in a {@link* java.lang.SecurityException}.**  @see #EXTRA_OUTPUT*/@SdkConstant(SdkConstantType.ACTIVITY_INTENT_ACTION)public final static String ACTION_IMAGE_CAPTURE = "android.media.action.IMAGE_CAPTURE";

android.media.action.VIDEO_CAMERA

 /*** The name of the Intent action used to launch a camera in video mode.*/@SdkConstant(SdkConstantType.ACTIVITY_INTENT_ACTION)public static final String INTENT_ACTION_VIDEO_CAMERA = "android.media.action.VIDEO_CAMERA";

自定义相机开发

详细的流程和模版代码可参看：控制相机文档

这里简要介绍下源码中给出的流程

1. client for camera service 管理Camera硬件资源
2. 包含：a.image capture settingsb.start/stop previewc.snap picturesd.retrieve frames for encoding for video
****************************
/**The Camera class is used to set image capture settings, start/stop preview,
snap pictures, and retrieve frames for encoding for video.  This class is a
client for the Camera service, which manages the actual camera hardware.
**/1. 需要申请权限2. 描述相机使用的features****************************
/*** To access the device camera, you must declare the* {@link android.Manifest.permission#CAMERA} permission in your Android* Manifest. Also be sure to include the manifest element to declare camera features used by *    * your application.* For example, if you use the camera and auto-focus feature, your Manifest* should include the following:</p>* <pre> &lt;uses-permission android:name="android.permission.CAMERA" />* &lt;uses-feature android:name="android.hardware.camera" />* &lt;uses-feature android:name="android.hardware.camera.autofocus" /></pre>**/拍照流程1. open(int)2. getParameters() and modify3. setDisplayOrientation(int)4. setPreviewDisplay(SurfaceHolder)5. startPreview()6. takePicture(Camera.ShutterCallback,* Camera.PictureCallback, Camera.PictureCallback, Camera.PictureCallback)****************************
/*** <p>To take pictures with this class, use the following steps:</p>** <ol>* <li>Obtain an instance of Camera from {@link #open(int)}.** <li>Get existing (default) settings with {@link #getParameters()}.** <li>If necessary, modify the returned {@link Camera.Parameters} object and call* {@link #setParameters(Camera.Parameters)}.** <li>Call {@link #setDisplayOrientation(int)} to ensure correct orientation of preview.** <li><b>Important</b>: Pass a fully initialized {@link SurfaceHolder} to* {@link #setPreviewDisplay(SurfaceHolder)}.  Without a surface, the camera* will be unable to start the preview.** <li><b>Important</b>: Call {@link #startPreview()} to start updating the* preview surface.  Preview must be started before you can take a picture.** <li>When you want, call {@link #takePicture(Camera.ShutterCallback,* Camera.PictureCallback, Camera.PictureCallback, Camera.PictureCallback)} to* capture a photo.  Wait for the callbacks to provide the actual image data.** <li>After taking a picture, preview display will have stopped.  To take more* photos, call {@link #startPreview()} again first.**/销毁1. stopPreview()2. release()****************************/** <li>Call {@link #stopPreview()} to stop updating the preview surface.** <li><b>Important:</b> Call {@link #release()} to release the camera for* use by other applications.  Applications should release the camera* immediately in {@link android.app.Activity#onPause()} (and re-{@link #open()}* it in {@link android.app.Activity#onResume()}).* </ol>**/切换视频模式1. Obtain and initialize a Camera and start preview2. unlock()3. android.media.MediaRecorder#setCamera(Camera)****************************
/** <p>To quickly switch to video recording mode, use these steps:</p>** <ol>* <li>Obtain and initialize a Camera and start preview as described above.** <li>Call {@link #unlock()} to allow the media process to access the camera.** <li>Pass the camera to {@link android.media.MediaRecorder#setCamera(Camera)}.* See {@link android.media.MediaRecorder} information about video recording.** <li>When finished recording, call {@link #reconnect()} to re-acquire* and re-lock the camera.** <li>If desired, restart preview and take more photos or videos.** <li>Call {@link #stopPreview()} and {@link #release()} as described above.* </ol>**/1. 非线程安全，一定要做好线程调度控制****************************/** <p>This class is not thread-safe, and is meant for use from one event thread.* Most long-running operations (preview, focus, photo capture, etc) happen* asynchronously and invoke callbacks as necessary.  Callbacks will be invoked* on the event thread {@link #open(int)} was called from.  This class's methods* must never be called from multiple threads at once.</p>**/1. 注意兼容性****************************/** <p class="caution"><strong>Caution:</strong> Different Android-powered devices* may have different hardware specifications, such as megapixel ratings and* auto-focus capabilities. In order for your application to be compatible with* more devices, you should not make assumptions about the device camera* specifications.</p>** <div class="special reference">* <h3>Developer Guides</h3>* <p>For more information about using cameras, read the* <a href="{@docRoot}guide/topics/media/camera.html">Camera</a> developer guide.</p>* </div>**/1. 高版本Android SDK推荐使用Camera2****************************/** @deprecated We recommend using the new {@link android.hardware.camera2} API for new*             applications.*/

更多细节请参看其他Camera1系列文章～～

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