7.24. ioctl VIDIOC_G_CROP, VIDIOC_S_CROP¶
VIDIOC_G_CROP - VIDIOC_S_CROP - Get or set the current cropping rectangle
int ioctl(int fd, VIDIOC_G_CROP, struct v4l2_crop *argp)
int ioctl(int fd, VIDIOC_S_CROP, const struct v4l2_crop *argp)
To query the cropping rectangle size and position applications set the
type field of a struct
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.
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 ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_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.
Type of the data stream, set by the application. Only these types
are valid here:
Cropping rectangle. The same co-ordinate system as for struct
Unfortunately in the case of multiplanar buffer types
this API was messed up with regards to how the
should be filled in. Some drivers only accepted the
_MPLANE buffer type while
other drivers only accepted a non-multiplanar buffer type (i.e. without the
_MPLANE at the end).
Starting with kernel 4.13 both variations are allowed.