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<html devsite>
<head>
<title>Camera</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
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<img style="float: right; margin: 0px 15px 15px 15px;" src="images/ape_fwk_hal_camera.png" alt="Android Camera HAL icon"/>
<p>Android's camera Hardware Abstraction Layer (HAL) connects the higher level
camera framework APIs in
<a href="http://developer.android.com/reference/android/hardware/package-summary.html">Camera 2</a>
to your underlying camera driver and hardware. The camera subsystem includes
implementations for camera pipeline components while the camera HAL provides
interfaces for use in implementing your version of these components.</p>
<aside class="note"><strong>Note:</strong> If you are implementing the Camera
HAL on Android 8.0 and higher, you must use the HIDL interface. For
information on the legacy components, see
<a href="#architecture-legacy">Legacy HAL components</a>.</aside>
<h2 id="architecture">Architecture</h2>
<p>The following figure and list describe the HAL components:</p>
<img src="images/ape_fwk_camera2.png" alt="Android camera architecture" id="figure1" />
<p class="img-caption"><strong>Figure 1.</strong> Camera architecture</p>
<dl>
<dt>Application framework</dt>
<dd>At the application framework level is the app's code, which uses the
<a href="https://developer.android.com/reference/android/hardware/camera2/package-summary">
Camera 2</a>
API to interact with the camera hardware. Internally, this code calls
corresponding <a href="https://developer.android.com/reference/android/os/Binder.html">Binder</a>
interfaces to access the native code that interacts with the camera.</dd>
<dt>AIDL</dt>
<dd>The binder interface associated with CameraService can be found at
<a href="https://android.googlesource.com/platform/frameworks/av/+/master/camera/aidl/android/hardware/ICameraService.aidl">frameworks/av/camera/aidl/android/hardware</a>.
The generated code calls the lower level native code to obtain access to the
physical camera and returns data that is used to create the
<a href="https://developer.android.com/reference/android/hardware/camera2/CameraDevice">
CameraDevice</a> and eventually
<a href="https://developer.android.com/reference/android/hardware/camera2/CameraCaptureSession.html">CameraCaptureSession</a>
objects at the framework level.</dd>
<dt>Native framework<dt>
<dd>This framework residing in <code>frameworks/av/</code> provides a
native equivalent to the
<a href="https://developer.android.com/reference/android/hardware/camera2/CameraDevice">CameraDevice</a>
and
<a href="https://developer.android.com/reference/android/hardware/camera2/CameraCaptureSession">CameraCaptureSession</a>
classes. See also, <a href="https://developer.android.com/ndk/reference/group/camera">
NDK camera2 reference</a>.</dd>
<dt>Binder IPC interface</dt>
<dd>The IPC binder interface facilitates communication over process boundaries.
There are several camera binder classes located in the
<code>frameworks/av/camera/camera/aidl/android/hardware</code> directory that
call into camera service.
<a href="https://android.googlesource.com/platform/frameworks/av/+/master/camera/aidl/android/hardware/ICameraService.aidl">ICameraService</a>
is the interface to the camera service;
<a href="https://android.googlesource.com/platform/frameworks/av/+/master/camera/aidl/android/hardware/camera2/ICameraDeviceUser.aidl">ICameraDeviceUser</a>
is the interface to a specific opened camera device; and
<a href="https://android.googlesource.com/platform/frameworks/av/+/master/camera/aidl/android/hardware/ICameraServiceListener.aidl">ICameraServiceListener</a>
and
<a href="https://android.googlesource.com/platform/frameworks/av/+/master/camera/aidl/android/hardware/camera2/ICameraDeviceCallbacks.aidl">ICameraDeviceCallbacks</a>
are the respective CameraService and CameraDevice callbacks to the application
framework.</dd>
<dt>Camera service</dt>
<dd>The camera service, located in
<code>frameworks/av/services/camera/libcameraservice/CameraService.cpp</code>,
is the actual code that interacts with the HAL.</dd>
<dt>HAL</dt>
<dd>The hardware abstraction layer defines the standard interface that the
camera service calls into and that you must implement to have your camera
hardware function correctly.</dd>
</dl>
<h2 id="implementing">Implementing the HAL</h2>
<p>The HAL sits between the camera driver and the higher level Android framework
and defines an interface you must implement so apps can correctly operate the
camera hardware. From Android 8.0, the Camera HAL interface is part of Project
<a href="/devices/architecture/treble">Treble</a> and the corresponding
<a href="/devices/architecture/hidl/">HIDL</a> interfaces are defined in
<a href="https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/">hardware/interfaces/camera</a>.</p>
<p>A typical binderized HAL must implement the following HIDL interfaces:</p>
<ul>
<li><a href="/reference/hidl/android/hardware/camera/provider/2.4/ICameraProvider">ICameraProvider</a>:
For enumerating individual devices and managing their status.</li>
<li><a href="/reference/hidl/android/hardware/camera/device/3.2/ICameraDevice">ICameraDevice</a>:
The camera device interface.</li>
<li><a href="/reference/hidl/android/hardware/camera/device/3.2/ICameraDeviceSession">ICameraDeviceSession</a>:
The active camera device session interface.</li>
</ul>
<p>Reference HIDL implementations are available for
<a href="https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/provider/2.4/default/CameraProvider.cpp">CameraProvider.cpp</a>,
<a href="https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/device/3.2/default/CameraDevice.cpp">CameraDevice.cpp</a>
and
<a href="https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/device/3.2/default/CameraDeviceSession.cpp">CameraDeviceSession.cpp</a>.
The implementation wraps old HALs that still use the
<a href="https://android.googlesource.com/platform/hardware/libhardware/+/master/include/hardware/camera3.h">legacy API</a>.
Starting with Android 8.0, Camera HAL implementations must use the HIDL API; use
of the legacy interface is not supported.</p>
<p>For more information on Treble and HAL development, see
<a href="https://source.android.com/devices/architecture/treble#treble-resources">Treble Resources</a>.</p>
<h2 id="legacy-hal">Legacy HAL components</h2>
<p>This section describes the architecture of the legacy HAL components and how to
implement the HAL. Camera HAL implementations on Android 8.0 and higher must use
the HIDL API instead, described above.</p>
<h3 id="architecture-legacy">Architecture (legacy)</h3>
<p>The following figure and list describe the legacy camera HAL components:</p>
<img src="images/ape_fwk_camera.png" alt="Android camera architecture" id="figure1" />
<p class="img-caption"><strong>Figure 1.</strong> Camera architecture</p>
<dl>
<dt>Application framework</dt>
<dd>At the application framework level is the app's code, which utilizes the
<a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
API to interact with the camera hardware. Internally, this code calls a
corresponding JNI glue class to access the native code that interacts with the
camera.</dd>
<dt>JNI</dt>
<dd>The JNI code associated with <a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
is located in
<code>frameworks/base/core/jni/android_hardware_Camera.cpp</code>. This code
calls the lower level native code to obtain access to the physical camera
and returns data that is used to create the
<a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
object at the framework level.</dd>
<dt>Native framework<dt>
<dd>The native framework defined in <code>frameworks/av/camera/Camera.cpp</code>
provides a native equivalent to the
<a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>
class. This class calls the IPC binder proxies to obtain access to the camera
service.</dd>
<dt>Binder IPC proxies</dt>
<dd>The IPC binder proxies facilitate communication over process boundaries.
There are three camera binder classes that are located in
<code>frameworks/av/camera</code> directory that calls into camera service.
ICameraService is the interface to the camera service, ICamera is the
interface to a specific opened camera device, and ICameraClient is the
device's interface back to the application framework.</dd>
<dt>Camera service</dt>
<dd>The camera service, located in
<code>frameworks/av/services/camera/libcameraservice/CameraService.cpp</code>,
is the actual code that interacts with the HAL.</dd>
<dt>HAL</dt>
<dd>The hardware abstraction layer defines the standard interface that the
camera service calls into and that you must implement to have your camera
hardware function correctly.</dd>
<dt>Kernel driver</dt>
<dd>The camera's driver interacts with the actual camera hardware and your
implementation of the HAL. The camera and driver must support YV12 and NV21
image formats to provide support for previewing the camera image on the
display and video recording.</dd>
</dl>
<h3 id="implementing-legacy">Implementing the HAL (legacy)</h3>
<p>The HAL sits between the camera driver and the higher level Android framework
and defines an interface you must implement so apps can correctly operate the
camera hardware. The HAL interface is defined in the
<code>hardware/libhardware/include/hardware/camera.h</code> and
<code>hardware/libhardware/include/hardware/camera_common.h</code> header files.
</p>
<p><code>camera_common.h</code> defines <code>camera_module</code>, a standard
structure to obtain general information about the camera, such as the camera ID
and properties common to all cameras (i.e., whether it is a front- or
back-facing camera).</p>
<p>
<code>camera.h</code> contains code that corresponds to
<a href="http://developer.android.com/reference/android/hardware/Camera.html">android.hardware.Camera</a>. This header file declares a
<code>camera_device</code> struct that in turn contains a
<code>camera_device_ops</code> struct with pointers to functions that implement
the HAL interface. For documentation on the camera parameters developers can
set, refer to <code>frameworks/av/include/camera/CameraParameters.h</code>.
These parameters are set with the function pointed to by <code>int
(*set_parameters)(struct camera_device *, const char *parms)</code> in the HAL.
</p>
<p>For an example of a HAL implementation, refer to the implementation for the
Galaxy Nexus HAL in <code>hardware/ti/omap4xxx/camera</code>.</p>
<h3 id="configuring">Configuring the shared library</h3>
<p>Set up the Android build system to correctly package the HAL implementation
into a shared library and copy it to the appropriate location by creating an
<code>Android.mk</code> file:</p>
<ol>
<li>Create a <code>device/<company_name>/<device_name>/camera</code>
directory to contain your library's source files.</li>
<li>Create an <code>Android.mk</code> file to build the shared library. Ensure
the Makefile contains the following lines:
<pre class="devsite-click-to-copy">
LOCAL_MODULE := camera.<device_name>
LOCAL_MODULE_RELATIVE_PATH := hw
</pre>
<p>Your library must be named <code>camera.<device_name></code>
(<code>.so</code> is appended automatically), so Android can correctly load the
library. For an example, see the Makefile for the Galaxy Nexus camera located in
<code>hardware/ti/omap4xxx/Android.mk</code>.</p></li>
<li>Specify your device has camera features by copying the necessary feature XML
files in the <code>frameworks/native/data/etc</code> directory with your
device's Makefile. For example, to specify your device has a camera flash and
can autofocus, add the following lines in your device's
<code><device>/<company_name>/<device_name>/device.mk</code>
Makefile:
<pre class="devsite-click-to-copy">
PRODUCT_COPY_FILES := \ ...
PRODUCT_COPY_FILES += \
frameworks/native/data/etc/android.hardware.camera.flash-autofocus.xml:system/etc/permissions/android.hardware.camera.flash-autofocus.xml \
</pre>
<p>For an example of a device Makefile, see
<code>device/samsung/tuna/device.mk</code>.</p></li>
<li>Declare your camera’s media codec, format, and resolution capabilities in
<code>device/<company_name>/<device_name>/media_profiles.xml</code>
and <code>device/<company_name>/<device_name>/media_codecs.xml</code>
XML files. For details, see
<a href="/devices/media/index.html#expose">Exposing codecs to the
framework</a>.</li>
<li>Add the following lines in your device's
<code>device/<company_name>/<device_name>/device.mk</code> Makefile
to copy the <code>media_profiles.xml</code> and <code>media_codecs.xml</code>
files to the appropriate location:
<pre class="devsite-click-to-copy">
# media config xml file
PRODUCT_COPY_FILES += \
<device>/<company>/<device>/media_profiles.xml:system/etc/media_profiles.xml
# media codec config xml file
PRODUCT_COPY_FILES += \
<device>/<company>/<device>/media_codecs.xml:system/etc/media_codecs.xml
</pre></li>
<li>To include the Camera app in your device's system image, specify it in the
<code>PRODUCT_PACKAGES</code> variable in your device's
<code>device/<company>/<device>/device.mk</code>
Makefile:
<pre class="devsite-click-to-copy">
PRODUCT_PACKAGES := \
Gallery2 \
...
</pre></li>
</ol>
</body>
</html>
|
