Video for Linux Two API Specification: Revision 0.24
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ioctl VIDIOC_G_CROP, VIDIOC_S_CROP

Name

VIDIOC_G_CROP, VIDIOC_S_CROP -- Get or set the current cropping rectangle

Synopsis

int ioctl(int fd, int request, struct v4l2_crop *argp);

int ioctl(int fd, int request, const struct v4l2_crop *argp);

Arguments

fd

File descriptor returned by open().

request

VIDIOC_G_CROP, VIDIOC_S_CROP

argp

Description

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.

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 1. struct v4l2_crop

enum v4l2_buf_typetypeType of the data stream, set by the application. Only these types are valid here: V4L2_BUF_TYPE_VIDEO_CAPTURE, V4L2_BUF_TYPE_VIDEO_OUTPUT, V4L2_BUF_TYPE_VIDEO_OVERLAY, and custom (driver defined) types with code V4L2_BUF_TYPE_PRIVATE and higher.
struct v4l2_rectcCropping rectangle. The same co-ordinate system as for struct v4l2_cropcap bounds is used.

Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately:

EINVAL

Cropping is not supported.

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