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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/v4l/selection-api-examples.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/userspace-api/media/v4l/selection-api-examples.rst | 84 |
1 files changed, 84 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 000000000..5f8e8a1f5 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/selection-api-examples.rst @@ -0,0 +1,84 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +******** +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; |