media: docs: move uAPI book to userspace-api/media

Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee3862 ("docs: Create a user-space API guide").

As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.

Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/selection-api-intro.rst b/Documentation/userspace-api/media/v4l/selection-api-intro.rst
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index 000000000000..0994ca25be5e
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+++ b/Documentation/userspace-api/media/v4l/selection-api-intro.rst
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+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+************
+Introduction
+************
+
+Some video capture devices can sample a subsection of a picture and
+shrink or enlarge it to an image of arbitrary size. Next, the devices
+can insert the image into larger one. Some video output devices can crop
+part of an input image, scale it up or down and insert it at an
+arbitrary scan line and horizontal offset into a video signal. We call
+these abilities cropping, scaling and composing.
+
+On a video *capture* device the source is a video signal, and the
+cropping target determine the area actually sampled. The sink is an
+image stored in a memory buffer. The composing area specifies which part
+of the buffer is actually written to by the hardware.
+
+On a video *output* device the source is an image in a memory buffer,
+and the cropping target is a part of an image to be shown on a display.
+The sink is the display or the graphics screen. The application may
+select the part of display where the image should be displayed. The size
+and position of such a window is controlled by the compose target.
+
+Rectangles for all cropping and composing targets are defined even if
+the device does supports neither cropping nor composing. Their size and
+position will be fixed in such a case. If the device does not support
+scaling then the cropping and composing rectangles have the same size.