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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2 3********4Examples5********6 7(A video capture device is assumed; change8``V4L2_BUF_TYPE_VIDEO_CAPTURE`` for other devices; change target to9``V4L2_SEL_TGT_COMPOSE_*`` family to configure composing area)10 11Example: Resetting the cropping parameters12==========================================13 14.. code-block:: c15 16 struct v4l2_selection sel = {17 .type = V4L2_BUF_TYPE_VIDEO_CAPTURE,18 .target = V4L2_SEL_TGT_CROP_DEFAULT,19 };20 ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);21 if (ret)22 exit(-1);23 sel.target = V4L2_SEL_TGT_CROP;24 ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);25 if (ret)26 exit(-1);27 28Setting a composing area on output of size of *at most* half of limit29placed at a center of a display.30 31Example: Simple downscaling32===========================33 34.. code-block:: c35 36 struct v4l2_selection sel = {37 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT,38 .target = V4L2_SEL_TGT_COMPOSE_BOUNDS,39 };40 struct v4l2_rect r;41 42 ret = ioctl(fd, VIDIOC_G_SELECTION, &sel);43 if (ret)44 exit(-1);45 /* setting smaller compose rectangle */46 r.width = sel.r.width / 2;47 r.height = sel.r.height / 2;48 r.left = sel.r.width / 4;49 r.top = sel.r.height / 4;50 sel.r = r;51 sel.target = V4L2_SEL_TGT_COMPOSE;52 sel.flags = V4L2_SEL_FLAG_LE;53 ret = ioctl(fd, VIDIOC_S_SELECTION, &sel);54 if (ret)55 exit(-1);56 57A video output device is assumed; change ``V4L2_BUF_TYPE_VIDEO_OUTPUT``58for other devices59 60Example: Querying for scaling factors61=====================================62 63.. code-block:: c64 65 struct v4l2_selection compose = {66 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT,67 .target = V4L2_SEL_TGT_COMPOSE,68 };69 struct v4l2_selection crop = {70 .type = V4L2_BUF_TYPE_VIDEO_OUTPUT,71 .target = V4L2_SEL_TGT_CROP,72 };73 double hscale, vscale;74 75 ret = ioctl(fd, VIDIOC_G_SELECTION, &compose);76 if (ret)77 exit(-1);78 ret = ioctl(fd, VIDIOC_G_SELECTION, &crop);79 if (ret)80 exit(-1);81 82 /* computing scaling factors */83 hscale = (double)compose.r.width / crop.r.width;84 vscale = (double)compose.r.height / crop.r.height;85