ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION

&manvol;

VIDIOC_G_SELECTION

VIDIOC_S_SELECTION

Get or set one of the selection rectangles

    	int ioctl
    	int fd
    	int request
    	struct v4l2_selection *argp

## Arguments

`fd`

- &fd;

`request`

- VIDIOC_G_SELECTION, VIDIOC_S_SELECTION

`argp`

## Description

### Experimental

This is an experimental interface and may change in the future.

The ioctls are used to query and configure selection rectangles.

To query the cropping (composing) rectangle set &v4l2-selection; type field to the respective buffer type. Do not use multiplanar buffers. Use `V4L2_BUF_TYPE_VIDEO_CAPTURE` instead of `V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`. Use `V4L2_BUF_TYPE_VIDEO_OUTPUT` instead of `V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`. The next step is setting the value of &v4l2-selection; target field to `V4L2_SEL_TGT_CROP` (`V4L2_SEL_TGT_COMPOSE`). Please refer to table v4l2-selections-common or selection-api for additional targets. The flags and reserved fields of &v4l2-selection; are ignored and they must be filled with zeros. The driver fills the rest of the structure or returns &EINVAL; if incorrect buffer type or target was used. If cropping (composing) is not supported then the active rectangle is not mutable and it is always equal to the bounds rectangle. Finally, the &v4l2-rect; r rectangle is filled with the current cropping (composing) coordinates. The coordinates are expressed in driver-dependent units. The only exception are rectangles for images in raw formats, whose coordinates are always expressed in pixels.

To change the cropping (composing) rectangle set the &v4l2-selection; type field to the respective buffer type. Do not use multiplanar buffers. Use `V4L2_BUF_TYPE_VIDEO_CAPTURE` instead of `V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`. Use `V4L2_BUF_TYPE_VIDEO_OUTPUT` instead of `V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`. The next step is setting the value of &v4l2-selection; target to `V4L2_SEL_TGT_CROP` (`V4L2_SEL_TGT_COMPOSE`). Please refer to table v4l2-selections-common or selection-api for additional targets. The &v4l2-rect; r rectangle need to be set to the desired active area. Field &v4l2-selection; reserved is ignored and must be filled with zeros. The driver may adjust coordinates of the requested rectangle. An application may introduce constraints to control rounding behaviour. The &v4l2-selection; flags field must be set to one of the following:

- `0` - The driver can adjust the rectangle size freely and shall choose a crop/compose rectangle as close as possible to the requested one.

- `V4L2_SEL_FLAG_GE` - The driver is not allowed to shrink the rectangle. The original rectangle must lay inside the adjusted one.

- `V4L2_SEL_FLAG_LE` - The driver is not allowed to enlarge the rectangle. The adjusted rectangle must lay inside the original one.

- `V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE` - The driver must choose the size exactly the same as in the requested rectangle.

Please refer to sel-const-adjust.

The driver may have to adjusts the requested dimensions against hardware limits and other parts as the pipeline, i.e. the bounds given by the capture/output window or TV display. The closest possible values of horizontal and vertical offset and sizes are chosen according to following priority:

1. Satisfy constraints from &v4l2-selection; flags.

2. Adjust width, height, left, and top to hardware limits and alignments.

3. Keep center of adjusted rectangle as close as possible to the original one.

4. Keep width and height as close as possible to original ones.

5. Keep horizontal and vertical offset as close as possible to original ones.

On success the &v4l2-rect; r field contains the adjusted rectangle. When the parameters are unsuitable the application may modify the cropping (composing) or image parameters and repeat the cycle until satisfactory parameters have been negotiated. If constraints flags have to be violated at then ERANGE is returned. The error indicates that there exist no rectangle that satisfies the constraints.

Selection targets and flags are documented in v4l2-selections-common.

### Size adjustments with constraint flags.

Behaviour of rectangle adjustment for different constraint flags.

## struct v4l2_selection

&cs-str;
__u32 | type | Type of the buffer (from &v4l2-buf-type;).
__u32 | target | Used to select between cropping and composing rectangles.
__u32 | flags | Flags controlling the selection rectangle adjustments, refer to selection flags.
&v4l2-rect; | r | The selection rectangle.
__u32 | reserved[9] | Reserved fields for future use.

&return-value;

EINVAL

- Given buffer type type or the selection target target is not supported, or the flags argument is not valid.

ERANGE

- It is not possible to adjust &v4l2-rect; r rectangle to satisfy all contraints given in the flags argument.

EBUSY

- It is not possible to apply change of the selection rectangle at the moment. Usually because streaming is in progress.