.. 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;