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author | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2020-03-04 10:21:39 +0100 |
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committer | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2020-04-14 10:31:49 +0200 |
commit | 54f38fcae536ea202ce7d6a359521492fba30c1f (patch) | |
tree | dd1a2b36d8de0b13702f2716526ad3b91650e090 /Documentation/userspace-api/media/v4l/selection-api-examples.rst | |
parent | 5dfb8db56b273740a76e8687ee7efb4b2c0ec83b (diff) | |
download | linux-stable-54f38fcae536ea202ce7d6a359521492fba30c1f.tar.gz linux-stable-54f38fcae536ea202ce7d6a359521492fba30c1f.tar.bz2 linux-stable-54f38fcae536ea202ce7d6a359521492fba30c1f.zip |
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>
Diffstat (limited to 'Documentation/userspace-api/media/v4l/selection-api-examples.rst')
-rw-r--r-- | Documentation/userspace-api/media/v4l/selection-api-examples.rst | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/selection-api-examples.rst b/Documentation/userspace-api/media/v4l/selection-api-examples.rst new file mode 100644 index 000000000000..2f4027211129 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/selection-api-examples.rst @@ -0,0 +1,91 @@ +.. 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 + +******** +Examples +******** + +(A video capture device is assumed; change +``V4L2_BUF_TYPE_VIDEO_CAPTURE`` for other devices; change target to +``V4L2_SEL_TGT_COMPOSE_*`` family to configure composing area) + +Example: Resetting the cropping parameters +========================================== + +.. code-block:: c + + struct v4l2_selection sel = { + .type = V4L2_BUF_TYPE_VIDEO_CAPTURE, + .target = V4L2_SEL_TGT_CROP_DEFAULT, + }; + ret = ioctl(fd, VIDIOC_G_SELECTION, &sel); + if (ret) + exit(-1); + sel.target = V4L2_SEL_TGT_CROP; + ret = ioctl(fd, VIDIOC_S_SELECTION, &sel); + if (ret) + exit(-1); + +Setting a composing area on output of size of *at most* half of limit +placed at a center of a display. + +Example: Simple downscaling +=========================== + +.. code-block:: c + + struct v4l2_selection sel = { + .type = V4L2_BUF_TYPE_VIDEO_OUTPUT, + .target = V4L2_SEL_TGT_COMPOSE_BOUNDS, + }; + struct v4l2_rect r; + + ret = ioctl(fd, VIDIOC_G_SELECTION, &sel); + if (ret) + exit(-1); + /* setting smaller compose rectangle */ + r.width = sel.r.width / 2; + r.height = sel.r.height / 2; + r.left = sel.r.width / 4; + r.top = sel.r.height / 4; + sel.r = r; + sel.target = V4L2_SEL_TGT_COMPOSE; + sel.flags = V4L2_SEL_FLAG_LE; + ret = ioctl(fd, VIDIOC_S_SELECTION, &sel); + if (ret) + exit(-1); + +A video output device is assumed; change ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` +for other devices + +Example: Querying for scaling factors +===================================== + +.. code-block:: c + + struct v4l2_selection compose = { + .type = V4L2_BUF_TYPE_VIDEO_OUTPUT, + .target = V4L2_SEL_TGT_COMPOSE, + }; + struct v4l2_selection crop = { + .type = V4L2_BUF_TYPE_VIDEO_OUTPUT, + .target = V4L2_SEL_TGT_CROP, + }; + double hscale, vscale; + + ret = ioctl(fd, VIDIOC_G_SELECTION, &compose); + if (ret) + exit(-1); + ret = ioctl(fd, VIDIOC_G_SELECTION, &crop); + if (ret) + exit(-1); + + /* computing scaling factors */ + hscale = (double)compose.r.width / crop.r.width; + vscale = (double)compose.r.height / crop.r.height; |