@@ -6,31 +6,34 @@
Comparison with old cropping API
********************************
-The selection API was introduced to cope with deficiencies of previous
-:ref:`API <crop>`, that was designed to control simple capture
-devices. Later the cropping API was adopted by video output drivers. The
-ioctls are used to select a part of the display were the video signal is
-inserted. It should be considered as an API abuse because the described
-operation is actually the composing. The selection API makes a clear
-distinction between composing and cropping operations by setting the
-appropriate targets. The V4L2 API lacks any support for composing to and
-cropping from an image inside a memory buffer. The application could
-configure a capture device to fill only a part of an image by abusing
-V4L2 API. Cropping a smaller image from a larger one is achieved by
-setting the field ``bytesperline`` at struct
-:c:type:`v4l2_pix_format`.
-Introducing an image offsets could be done by modifying field ``m_userptr``
-at struct
-:c:type:`v4l2_buffer` before calling
-:ref:`VIDIOC_QBUF`. Those operations should be avoided because they are not
-portable (endianness), and do not work for macroblock and Bayer formats
-and mmap buffers. The selection API deals with configuration of buffer
+The selection API was introduced to cope with deficiencies of the
+older :ref:`CROP API <crop>`, that was designed to control simple
+capture devices. Later the cropping API was adopted by video output
+drivers. The ioctls are used to select a part of the display were the
+video signal is inserted. It should be considered as an API abuse
+because the described operation is actually the composing. The
+selection API makes a clear distinction between composing and cropping
+operations by setting the appropriate targets.
+
+The V4L2 API lacks any support for composing to and cropping from an
+image inside a memory buffer. The application could configure a
+capture device to fill only a part of an image by abusing V4L2
+API. Cropping a smaller image from a larger one is achieved by setting
+the field ``bytesperline`` at struct :c:type:`v4l2_pix_format`.
+Introducing an image offsets could be done by modifying field
+``m_userptr`` at struct :c:type:`v4l2_buffer` before calling
+:ref:`VIDIOC_QBUF <VIDIOC_QBUF>`. Those operations should be avoided
+because they are not portable (endianness), and do not work for
+macroblock and Bayer formats and mmap buffers.
+
+The selection API deals with configuration of buffer
cropping/composing in a clear, intuitive and portable way. Next, with
the selection API the concepts of the padded target and constraints
-flags are introduced. Finally, struct :c:type:`v4l2_crop`
-and struct :c:type:`v4l2_cropcap` have no reserved
-fields. Therefore there is no way to extend their functionality. The new
-struct :c:type:`v4l2_selection` provides a lot of place
-for future extensions. Driver developers are encouraged to implement
-only selection API. The former cropping API would be simulated using the
-new one.
+flags are introduced. Finally, struct :c:type:`v4l2_crop` and struct
+:c:type:`v4l2_cropcap` have no reserved fields. Therefore there is no
+way to extend their functionality. The new struct
+:c:type:`v4l2_selection` provides a lot of place for future
+extensions.
+
+Driver developers are encouraged to implement only selection API. The
+former cropping API would be simulated using the new one.
Split section "Comparison with old cropping API" in paragraphs for easier reading and improve visible links text. Cc: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net> --- Changed v1 -> v2: nothing. --- .../media/uapi/v4l/selection-api-vs-crop-api.rst | 55 ++++++++++++---------- 1 file changed, 29 insertions(+), 26 deletions(-)