92 lines
2.4 KiB
ReStructuredText
92 lines
2.4 KiB
ReStructuredText
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.. Permission is granted to copy, distribute and/or modify this
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.. document under the terms of the GNU Free Documentation License,
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.. Version 1.1 or any later version published by the Free Software
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.. Foundation, with no Invariant Sections, no Front-Cover Texts
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.. and no Back-Cover Texts. A copy of the license is included at
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.. Documentation/media/uapi/fdl-appendix.rst.
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..
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.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
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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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