VIDIOC_G_CROP, VIDIOC_S_CROP — Get or set the current cropping rectangle
int ioctl( | int fd, |
| int request, | |
struct v4l2_crop *argp); |
int ioctl( | int fd, |
| int request, | |
const struct v4l2_crop *argp); |
To query the cropping rectangle size and position
applications set the type field of a
v4l2_crop structure to the respective buffer
(stream) type and call the VIDIOC_G_CROP ioctl
with a pointer to this structure. The driver fills the rest of the
structure or returns the EINVAL error code if cropping is not supported.
To change the cropping rectangle applications initialize the
type and struct v4l2_rect substructure named
c of a v4l2_crop structure and call the
VIDIOC_S_CROP ioctl with a pointer to this
structure.
Do not use the multiplanar buffer types. Use V4L2_BUF_TYPE_VIDEO_CAPTURE
instead of V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
and use V4L2_BUF_TYPE_VIDEO_OUTPUT instead of
V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE.
The driver first adjusts the requested dimensions against hardware limits, i. e. the bounds given by the capture/output window, and it rounds to the closest possible values of horizontal and vertical offset, width and height. In particular the driver must round the vertical offset of the cropping rectangle to frame lines modulo two, such that the field order cannot be confused.
Second the driver adjusts the image size (the opposite rectangle of the scaling process, source or target depending on the data direction) to the closest size possible while maintaining the current horizontal and vertical scaling factor.
Finally the driver programs the hardware with the actual
cropping and image parameters. VIDIOC_S_CROP is a
write-only ioctl, it does not return the actual parameters. To query
them applications must call VIDIOC_G_CROP and
VIDIOC_G_FMT. When the parameters are unsuitable the application may
modify the cropping or image parameters and repeat the cycle until
satisfactory parameters have been negotiated.
When cropping is not supported then no parameters are
changed and VIDIOC_S_CROP returns the
EINVAL error code.
Table A.55. struct v4l2_crop
| __u32 | type | Type of the data stream, set by the application.
Only these types are valid here: V4L2_BUF_TYPE_VIDEO_CAPTURE,
V4L2_BUF_TYPE_VIDEO_OUTPUT and
V4L2_BUF_TYPE_VIDEO_OVERLAY. See Table 3.3, “enum v4l2_buf_type”. |
| struct v4l2_rect | c | Cropping rectangle. The same co-ordinate system as
for struct v4l2_cropcap bounds is used. |
On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.