ref-manual: Updated image_types.bbclass description.

The "image_types" class is now inherited mandatorily in
image.bbclass through the variable IMGCLASSES.  Users do not
have to inherit it in their customized image type bbclass.
They also do not have to put it in IMAGE_CLASSES.

(From yocto-docs rev: 9d71cd281864478c76e40fa6e0b9cd0055f131c0)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-classes.xml

@@ -1314,28 +1314,35 @@
     <title><filename>image_types.bbclass</filename></title>
 
     <para>
-        The <filename>image_types</filename> class defines all of
-        the standard image output types that you can enable through the
+        The <filename>image_types</filename> class defines all of the
+        standard image output types that you can enable through the
         <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link>
         variable.
-        You can use this class as a reference on how to add support for custom
-        image output types.
+        You can use this class as a reference on how to add support for
+        custom image output types.
     </para>
 
     <para>
-        By default, this class is enabled through the
-        <link linkend='var-IMAGE_CLASSES'><filename>IMAGE_CLASSES</filename></link>
-        variable in
-        <link linkend='ref-classes-image'><filename>image.bbclass</filename></link>.
-        If you define your own image types using a custom BitBake class and
-        then use <filename>IMAGE_CLASSES</filename> to enable it, the custom
-        class must either inherit <filename>image_types</filename> or
-        <filename>image_types</filename> must also appear in
-        <filename>IMAGE_CLASSES</filename>.
+        By default, the
+        <link linkend='ref-classes-image'><filename>image</filename></link>
+        class automatically enables the <filename>image_types</filename> class.
+        The <filename>image</filename> class uses the
+        <filename>IMGCLASSES</filename> variable as follows:
+        <literallayout class='monospaced'>
+     IMGCLASSES = "rootfs_${IMAGE_PKGTYPE} image_types ${IMAGE_CLASSES}"
+     IMGCLASSES += "${@['populate_sdk_base', 'populate_sdk_ext']['linux' in d.getVar("SDK_OS")]}"
+     IMGCLASSES += "${@bb.utils.contains_any('IMAGE_FSTYPES', 'live iso hddimg', 'image-live', '', d)}"
+     IMGCLASSES += "${@bb.utils.contains('IMAGE_FSTYPES', 'container', 'image-container', '', d)}"
+     IMGCLASSES += "image_types_wic"
+     IMGCLASSES += "rootfs-postcommands"
+     IMGCLASSES += "image-postinst-intercepts"
+     inherit ${IMGCLASSES}
+        </literallayout>
     </para>
 
     <para>
-        This class also handles conversion and compression of images.
+        The <filename>image_types</filename> class also handles conversion and
+        compression of images.
         <note>
             To build a VMware VMDK image, you need to add "wic.vmdk" to
             <filename>IMAGE_FSTYPES</filename>.