src/devices/camera/camera.jd

page.title=Camera HAL overview
@jd:body

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<p>Android's camera HAL connects the higher level
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.
The following figure and list describe the components involved and where to find the source for each:
</p>

<p><img src="images/camera_hal.png"></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 the <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.</p>

  <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>


<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 that you must implement so that 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 an important struct, <code>camera_module</code>, which defines a standard
structure to obtain general information about the camera, such as its ID and properties
that are common to all cameras such as whether or not it is a front or back-facing camera.
</p>

<p>
<code>camera.h</code> contains the code that corresponds mainly with
<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 contains a <code>camera_device_ops</code> struct with function pointers
that point to functions that implement the HAL interface. For documentation on the
different types of camera parameters that a developer can set, 
see the <code>frameworks/av/include/camera/CameraParameters.h</code> file.
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, see the implementation for the Galaxy Nexus HAL in
<code>hardware/ti/omap4xxx/camera</code>.</p>


<h2 id="configuring">Configuring the Shared Library</h2>
<p>You need to 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:

<ol>
  <li>Create a <code>device/&lt;company_name&gt;/&lt;device_name&gt;/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 that the Makefile contains the following lines:
<pre>
LOCAL_MODULE := camera.&lt;device_name&gt;
LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw
</pre>
<p>Notice that your library must be named <code>camera.&lt;device_name&gt;</code> (<code>.so</code> is appended automatically),
so that 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 that 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 that your device has a camera flash and can autofocus,
add the following lines in your device's
<code>&lt;device&gt;/&lt;company_name&gt;/&lt;device_name&gt;/device.mk</code> Makefile:

<pre class="no-pretty-print">
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/&lt;company_name&gt;/&lt;device_name&gt;/media_profiles.xml</code> and
<code>device/&lt;company_name&gt;/&lt;device_name&gt;/media_codecs.xml</code> XML files.
 For more information, see <a href="{@docRoot}devices/media.html#expose"> Exposing
 Codecs and Profiles to the Framework</a> for information on how to do this.
</p></code>

</li>

<li>Add the following lines in your device's
   <code>device/&lt;company_name&gt;/&lt;device_name&gt;/device.mk</code> 
  Makefile to copy the <code>media_profiles.xml</code>
and <code>media_codecs.xml</code> files to the appropriate location:
<pre>
# media config xml file
PRODUCT_COPY_FILES += \
    &lt;device&gt;/&lt;company_name&gt;/&lt;device_name&gt;/media_profiles.xml:system/etc/media_profiles.xml

# media codec config xml file
PRODUCT_COPY_FILES += \
    &lt;device&gt;/&lt;company_name&gt;/&lt;device_name&gt;/media_codecs.xml:system/etc/media_codecs.xml
</pre>
</li>

<li>
<p>Declare that you want to include the Camera app in your device's system image by
specifying it in the <code>PRODUCT_PACKAGES</code> variable in your device's
   <code>device/&lt;company_name&gt;/&lt;device_name&gt;/device.mk</code> 
  Makefile:</p>
<pre>
PRODUCT_PACKAGES := \
Gallery2 \
...
</pre>
</li>

</ol>