Greg Kroah-Hartman
598cf27219
Link: https://lore.kernel.org/r/20260217200002.683975158@linuxfoundation.org Tested-by: Florian Fainelli <florian.fainelli@broadcom.com> Tested-by: Takeshi Ogasawara <takeshi.ogasawara@futuring-girl.com> Tested-by: Peter Schneider <pschneider1968@googlemail.com> Tested-by: Jon Hunter <jonathanh@nvidia.com> Tested-by: Salvatore Bonaccorso <carnil@debian.org> Tested-by: Brett A C Sheffield <bacs@librecast.net> Tested-by: Mark Brown <broonie@kernel.org> Tested-by: Luna Jernberg <droidbittin@gmail.com> Tested-by: Ronald Warsow <rwarsow@gmx.de> Tested-by: Justin M. Forbes <jforbes@fedoraproject.org> Tested-by: Ron Economos <re@w6rz.net> Tested-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
86 lines
2.0 KiB
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86 lines
2.0 KiB
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. c:namespace:: V4L
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********
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Examples
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********
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(A video capture device is assumed; change
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``V4L2_BUF_TYPE_VIDEO_CAPTURE`` for other devices; change target to
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``V4L2_SEL_TGT_COMPOSE_*`` family to configure composing area)
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Example: Resetting the cropping parameters
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==========================================
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.. code-block:: c
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struct v4l2_selection sel = {
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.type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
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.target = V4L2_SEL_TGT_CROP_DEFAULT,
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};
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ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);
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if (ret)
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exit(-1);
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sel.target = V4L2_SEL_TGT_CROP;
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ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);
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if (ret)
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exit(-1);
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Setting a composing area on output of size of *at most* half of limit
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placed at a center of a display.
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Example: Simple downscaling
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===========================
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.. code-block:: c
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struct v4l2_selection sel = {
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.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
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.target = V4L2_SEL_TGT_COMPOSE_BOUNDS,
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};
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struct v4l2_rect r;
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ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);
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if (ret)
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exit(-1);
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/* setting smaller compose rectangle */
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r.width = sel.r.width / 2;
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r.height = sel.r.height / 2;
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r.left = sel.r.width / 4;
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r.top = sel.r.height / 4;
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sel.r = r;
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sel.target = V4L2_SEL_TGT_COMPOSE;
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sel.flags = V4L2_SEL_FLAG_LE;
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ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);
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if (ret)
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exit(-1);
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A video output device is assumed; change ``V4L2_BUF_TYPE_VIDEO_OUTPUT``
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for other devices
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Example: Querying for scaling factors
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=====================================
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.. code-block:: c
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struct v4l2_selection compose = {
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.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
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.target = V4L2_SEL_TGT_COMPOSE,
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};
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struct v4l2_selection crop = {
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.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
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.target = V4L2_SEL_TGT_CROP,
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};
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double hscale, vscale;
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ret = ioctl(fd, VIDIOC_G_SELECTION, &compose);
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if (ret)
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exit(-1);
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ret = ioctl(fd, VIDIOC_G_SELECTION, &crop);
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if (ret)
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exit(-1);
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/* computing scaling factors */
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hscale = (double)compose.r.width / crop.r.width;
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vscale = (double)compose.r.height / crop.r.height;
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