Clay Murphy | b6e5f5b | 2013-10-21 17:01:06 -0700 | [diff] [blame] | 1 | page.title=Camera HAL overview |
Robert Ly | 35f2fda | 2013-01-29 16:27:05 -0800 | [diff] [blame] | 2 | @jd:body |
| 3 | |
| 4 | <!-- |
Clay Murphy | b6e5f5b | 2013-10-21 17:01:06 -0700 | [diff] [blame] | 5 | Copyright 2013 The Android Open Source Project |
Robert Ly | 35f2fda | 2013-01-29 16:27:05 -0800 | [diff] [blame] | 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
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| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
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| 19 | <div id="qv-wrapper"> |
| 20 | <div id="qv"> |
| 21 | <h2>In this document</h2> |
| 22 | <ol id="auto-toc"> |
| 23 | </ol> |
| 24 | </div> |
| 25 | </div> |
| 26 | |
| 27 | <p>Android's camera HAL connects the higher level |
| 28 | camera framework APIs in <a href="http://developer.android.com/reference/android/hardware/package-summary.html">android.hardware</a> to your underlying camera driver and hardware. |
| 29 | The following figure and list describe the components involved and where to find the source for each: |
| 30 | </p> |
| 31 | |
| 32 | <p><img src="images/camera_hal.png"></p> |
| 33 | |
| 34 | <dl> |
| 35 | |
| 36 | <dt>Application framework</dt> |
| 37 | <dd>At the application framework level is the app's code, which utilizes the <a |
| 38 | href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a> |
| 39 | API to interact with the camera hardware. Internally, this code calls a corresponding JNI glue class |
| 40 | to access the native code that interacts with the camera.</dd> |
| 41 | |
| 42 | <dt>JNI</dt> |
| 43 | <dd>The JNI code associated with <a |
| 44 | href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a> is located in |
| 45 | <code>frameworks/base/core/jni/android_hardware_Camera.cpp</code>. This code calls the lower level |
| 46 | native code to obtain access to the physical camera and returns data that is used to create the |
| 47 | <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a> object at the framework level.</dd> |
| 48 | |
| 49 | <dt>Native framework<dt> |
| 50 | <dd>The native framework defined in <code>frameworks/av/camera/Camera.cpp</code> provides a native equivalent |
| 51 | to the <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a> class. |
| 52 | This class calls the IPC binder proxies to obtain access to the camera service.</dd> |
| 53 | |
| 54 | <dt>Binder IPC proxies</dt> |
| 55 | <dd>The IPC binder proxies facilitate communication over process boundaries. There are three camera binder |
| 56 | classes that are located in the <code>frameworks/av/camera</code> directory that calls into |
| 57 | camera service. ICameraService is the interface to the camera service, ICamera is the interface |
| 58 | to a specific opened camera device, and ICameraClient is the device's interface back to the application framework.</dd> |
| 59 | |
| 60 | <dt>Camera service</dt> |
| 61 | <dd>The camera service, located in <code>frameworks/av/services/camera/libcameraservice/CameraService.cpp</code>, is the actual code that interacts with the HAL.</p> |
| 62 | |
| 63 | <dt>HAL</dt> |
| 64 | <dd>The hardware abstraction layer defines the standard interface that the camera service calls into and that |
| 65 | you must implement to have your camera hardware function correctly. |
| 66 | </dd> |
| 67 | |
| 68 | <dt>Kernel driver</dt> |
| 69 | <dd>The camera's driver interacts with the actual camera hardware and your implementation of the HAL. The |
| 70 | camera and driver must support YV12 and NV21 image formats to provide support for |
| 71 | previewing the camera image on the display and video recording.</dd> |
| 72 | </dl> |
| 73 | |
| 74 | |
| 75 | <h2 id="implementing">Implementing the HAL</h2> |
| 76 | <p>The HAL sits between the camera driver and the higher level Android framework |
| 77 | and defines an interface that you must implement so that apps can |
| 78 | correctly operate the camera hardware. The HAL interface is defined in the |
| 79 | <code>hardware/libhardware/include/hardware/camera.h</code> and |
| 80 | <code>hardware/libhardware/include/hardware/camera_common.h</code> header files. |
| 81 | </p> |
| 82 | |
| 83 | <p> |
| 84 | <code>camera_common.h</code> defines an important struct, <code>camera_module</code>, which defines a standard |
| 85 | structure to obtain general information about the camera, such as its ID and properties |
| 86 | that are common to all cameras such as whether or not it is a front or back-facing camera. |
| 87 | </p> |
| 88 | |
| 89 | <p> |
| 90 | <code>camera.h</code> contains the code that corresponds mainly with |
| 91 | <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>. This header file declares a <code>camera_device</code> |
| 92 | struct that contains a <code>camera_device_ops</code> struct with function pointers |
| 93 | that point to functions that implement the HAL interface. For documentation on the |
| 94 | different types of camera parameters that a developer can set, |
| 95 | see the <code>frameworks/av/include/camera/CameraParameters.h</code> file. |
| 96 | These parameters are set with the function pointed to by |
| 97 | <code>int (*set_parameters)(struct camera_device *, const char *parms)</code> in the HAL. |
| 98 | </p> |
| 99 | |
| 100 | <p>For an example of a HAL implementation, see the implementation for the Galaxy Nexus HAL in |
| 101 | <code>hardware/ti/omap4xxx/camera</code>.</p> |
| 102 | |
| 103 | |
| 104 | <h2 id="configuring">Configuring the Shared Library</h2> |
| 105 | <p>You need to set up the Android build system to |
| 106 | correctly package the HAL implementation into a shared library and copy it to the |
| 107 | appropriate location by creating an <code>Android.mk</code> file: |
| 108 | |
| 109 | <ol> |
| 110 | <li>Create a <code>device/<company_name>/<device_name>/camera</code> directory to contain your |
| 111 | library's source files.</li> |
| 112 | <li>Create an <code>Android.mk</code> file to build the shared library. Ensure that the Makefile contains the following lines: |
| 113 | <pre> |
| 114 | LOCAL_MODULE := camera.<device_name> |
Colin Cross | 4ec43f0 | 2014-01-24 21:00:32 -0800 | [diff] [blame] | 115 | LOCAL_MODULE_RELATIVE_PATH := hw |
Robert Ly | 35f2fda | 2013-01-29 16:27:05 -0800 | [diff] [blame] | 116 | </pre> |
| 117 | <p>Notice that your library must be named <code>camera.<device_name></code> (<code>.so</code> is appended automatically), |
| 118 | so that Android can correctly load the library. For an example, see the Makefile |
| 119 | for the Galaxy Nexus camera located in <code>hardware/ti/omap4xxx/Android.mk</code>.</p> |
| 120 | |
| 121 | </li> |
| 122 | <li>Specify that your device has camera features by copying the necessary feature XML files in the |
| 123 | <code>frameworks/native/data/etc</code> directory with your |
| 124 | device's Makefile. For example, to specify that your device has a camera flash and can autofocus, |
| 125 | add the following lines in your device's |
| 126 | <code><device>/<company_name>/<device_name>/device.mk</code> Makefile: |
| 127 | |
| 128 | <pre class="no-pretty-print"> |
| 129 | PRODUCT_COPY_FILES := \ ... |
| 130 | |
| 131 | PRODUCT_COPY_FILES += \ |
| 132 | frameworks/native/data/etc/android.hardware.camera.flash-autofocus.xml:system/etc/permissions/android.hardware.camera.flash-autofocus.xml \ |
| 133 | </pre> |
| 134 | |
| 135 | <p>For an example of a device Makefile, see <code>device/samsung/tuna/device.mk</code>.</p> |
| 136 | </li> |
| 137 | |
| 138 | <li>Declare your camera’s media codec, format, and resolution capabilities in |
| 139 | <code>device/<company_name>/<device_name>/media_profiles.xml</code> and |
| 140 | <code>device/<company_name>/<device_name>/media_codecs.xml</code> XML files. |
Clay Murphy | b6e5f5b | 2013-10-21 17:01:06 -0700 | [diff] [blame] | 141 | For more information, see <a href="{@docRoot}devices/media.html#expose"> Exposing |
Robert Ly | 35f2fda | 2013-01-29 16:27:05 -0800 | [diff] [blame] | 142 | Codecs and Profiles to the Framework</a> for information on how to do this. |
| 143 | </p></code> |
| 144 | |
| 145 | </li> |
| 146 | |
| 147 | <li>Add the following lines in your device's |
| 148 | <code>device/<company_name>/<device_name>/device.mk</code> |
| 149 | Makefile to copy the <code>media_profiles.xml</code> |
| 150 | and <code>media_codecs.xml</code> files to the appropriate location: |
| 151 | <pre> |
| 152 | # media config xml file |
| 153 | PRODUCT_COPY_FILES += \ |
| 154 | <device>/<company_name>/<device_name>/media_profiles.xml:system/etc/media_profiles.xml |
| 155 | |
| 156 | # media codec config xml file |
| 157 | PRODUCT_COPY_FILES += \ |
| 158 | <device>/<company_name>/<device_name>/media_codecs.xml:system/etc/media_codecs.xml |
| 159 | </pre> |
| 160 | </li> |
| 161 | |
| 162 | <li> |
| 163 | <p>Declare that you want to include the Camera app in your device's system image by |
| 164 | specifying it in the <code>PRODUCT_PACKAGES</code> variable in your device's |
| 165 | <code>device/<company_name>/<device_name>/device.mk</code> |
| 166 | Makefile:</p> |
| 167 | <pre> |
| 168 | PRODUCT_PACKAGES := \ |
| 169 | Gallery2 \ |
| 170 | ... |
| 171 | </pre> |
| 172 | </li> |
| 173 | |
Clay Murphy | 72bdea0 | 2013-06-18 16:44:01 -0700 | [diff] [blame] | 174 | </ol> |