Hans Verkuil wrote:
On Tuesday, March 29, 2011 11:22:17 Tomasz Stanislawski wrote:
Hans Verkuil wrote:
On Monday, March 28, 2011 17:19:54 Tomasz Stanislawski wrote:
Hello everyone,
This patch-set introduces new ioctls to V4L2 API. The new method for
configuration of cropping and composition is presented.
There is some confusion in understanding of a cropping in current version
of
V4L2. For CAPTURE devices cropping refers to choosing only a part of
input
data stream and processing it and storing it in a memory buffer. The
buffer is
fully filled by data. It is not possible to choose only a part of a
buffer for
being updated by hardware.
In case of OUTPUT devices, the whole content of a buffer is passed by
hardware
to output display. Cropping means selecting only a part of an output
display/signal. It is not possible to choose only a part for a memory
buffer
to be processed.
The overmentioned flaws in cropping API were discussed in post:
http://article.gmane.org/gmane.linux.drivers.video-input-
infrastructure/28945
A solution was proposed during brainstorming session in Warsaw.
Hello. Thank you for a quick comment.
I don't have time right now to review this RFC in-depth, but one thing
that
needs more attention is the relationship between these new ioctls and
CROPCAP.
And also how this relates to analog inputs (I don't think analog outputs
make
any sense). And would a COMPOSECAP ioctl make sense?
Maybe two new ioctl COMPOSECAP and EXTCROPCAP should be added.
For input CROPCAP maps to EXTCROPCAP, for output it maps to COMPOSECAP.
The output EXTCROPCAP would return dimentions of a buffer.
But in my opinion field v4l2_selection::bounds should be added to
structure below. In such a case G_EXTCROP could be used to obtain
cropping bounds.
There is more in CROPCAP than just the bounds. I'd have to think about this
myself.
1. Data structures.
The structure v4l2_crop used by current API lacks any place for further
extensions. Therefore new structure is proposed.
struct v4l2_selection {
u32 type;
struct v4l2_rect r;
u32 flags;
u32 reserved[10];
};
Where,
type - type of buffer queue: V4L2_BUF_TYPE_VIDEO_CAPTURE,
V4L2_BUF_TYPE_VIDEO_OUTPUT, etc.
r - selection rectangle
flags - control over coordinates adjustments
reserved - place for further extensions, adjust struct size to 64 bytes
At first, the distinction between cropping and composing was stated. The
cropping operation means choosing only part of input data bounding it by
a
cropping rectangle. All other data must be discarded. On the other
hand,
composing means pasting processed data into rectangular part of data
sink. The
sink may be output device, user buffer, etc.
2. Crop/Compose ioctl.
Four new ioctls would be added to V4L2.
Name
VIDIOC_S_EXTCROP - set cropping rectangle on an input of a device
Synopsis
int ioctl(fd, VIDIOC_S_EXTCROP, struct v4l2_selection *s)
Description:
The ioctl is used to configure:
- for input devices, a part of input data that is processed in
hardware
- for output devices, a part of a data buffer to be passed to
hardware
Drivers may adjust a cropping area. The adjustment can be
controlled
by v4l2_selection::flags. Please refer to Hints section.
- an adjusted crop rectangle is returned in v4l2_selection::r
Return value
On success 0 is returned, on error -1 and the errno variable is set
appropriately:
ERANGE - failed to find a rectangle that satisfy all constraints
EINVAL - incorrect buffer type, cropping not supported
-----------------------------------------------------------------
Name
VIDIOC_G_EXTCROP - get cropping rectangle on an input of a device
Synopsis
int ioctl(fd, VIDIOC_G_EXTCROP, struct v4l2_selection *s)
Description:
The ioctl is used to query:
- for input devices, a part of input data that is processed in
hardware
- for output devices, a part of data buffer to be passed to hardware
Return value
On success 0 is returned, on error -1 and the errno variable is set
appropriately:
EINVAL - incorrect buffer type, cropping not supported
-----------------------------------------------------------------
Name
VIDIOC_S_COMPOSE - set destination rectangle on an output of a device
Synopsis
int ioctl(fd, VIDIOC_S_COMPOSE, struct v4l2_selection *s)
Description:
The ioctl is used to configure:
- for input devices, a part of a data buffer that is filled by
hardware
- for output devices, a area on output device where image is inserted
Drivers may adjust a composing area. The adjustment can be controlled
by v4l2_selection::flags. Please refer to Hints section.
- an adjusted composing rectangle is returned in v4l2_selection::r
Return value
On success 0 is returned, on error -1 and the errno variable is set
appropriately:
ERANGE - failed to find a rectangle that satisfy all constraints
EINVAL - incorrect buffer type, composing not supported
-----------------------------------------------------------------
Name
VIDIOC_G_COMPOSE - get destination rectangle on an output of a device
Synopsis
int ioctl(fd, VIDIOC_G_COMPOSE, struct v4l2_selection *s)
Description:
The ioctl is used to query:
- for input devices, a part of a data buffer that is filled by
hardware
- for output devices, a area on output device where image is inserted
Return value
On success 0 is returned, on error -1 and the errno variable is set
appropriately:
EINVAL - incorrect buffer type, composing not supported
3. Hints
The v4l2_selection::flags field is used to give a driver a hint about
coordinate adjustments. Below one can find the proposition of adjustment
flags. The syntax is V4L2_SEL_{name}_{LE/GE}, where {name} refer to a
field in
struct v4l2_rect. The LE is abbreviation from "lesser or equal". It
prevents
the driver form increasing a parameter. In similar fashion GE means
"greater or
equal" and it disallows decreasing. Combining LE and GE flags prevents
the
driver from any adjustments of parameters. In such a manner, setting
flags
field to zero would give a driver a free hand in coordinate adjustment.
#define V4L2_SEL_WIDTH_GE 0x00000001
#define V4L2_SEL_WIDTH_LE 0x00000002
#define V4L2_SEL_HEIGHT_GE 0x00000004
#define V4L2_SEL_HEIGHT_LE 0x00000008
#define V4L2_SEL_LEFT_GE 0x00000010
#define V4L2_SEL_LEFT_LE 0x00000020
#define V4L2_SEL_TOP_GE 0x00000040
#define V4L2_SEL_TOP_LE 0x00000080
Wouldn't you also need similar flags for RIGHT and BOTTOM?
Regards,
Hans
Proposed flags refer to fields in v4l2_rect structure. These are left,
top, width and height. Fields bottom and right and not present in
v4l2_rect structure.
But what if I want to keep the bottom right corner fixed, and allow other
parameters to change? I don't think you can do that with the current set of
flags.
Regards,
Hans
You are right. New flags should be added:
#define V4L2_SEL_RIGHT_GE 0x00000100
#define V4L2_SEL_RIGHT_LE 0x00000200
#define V4L2_SEL_BOTTOM_GE 0x00000400
#define V4L2_SEL_BOTTOM_LE 0x00000800
They would be used to inform a driver about adjusting a bottom-right
corner. Right and bottom would be defined as:
right = v4l2_rect::left + v4l2_rect::width
bottom = v4l2_rect::top + v4l2_rect::height
Best regards,
Tomasz Stanislawski
Best regards,
Tomasz Stanislawski
#define V4L2_SEL_WIDTH_FIXED 0x00000003
#define V4L2_SEL_HEIGHT_FIXED 0x0000000c
#define V4L2_SEL_LEFT_FIXED 0x00000030
#define V4L2_SEL_TOP_FIXED 0x000000c0
#define V4L2_SEL_FIXED 0x000000ff
The hint flags may be useful in a following scenario. There is a sensor
with a
face detection functionality. An application receives information about a
position of a face on sensor array. Assume that the camera pipeline is
capable
of an image scaling. The application is capable of obtaining a location
of a
face using V4L2 controls. The task it to grab only part of image that
contains
a face, and store it to a framebuffer at a fixed window. Therefore
following
constrains have to be satisfied:
- the rectangle that contains a face must lay inside cropping area
- hardware is allowed only to access area inside window on the
framebuffer
Both constraints could be satisfied with two ioctl calls.
- VIDIOC_EXTCROP with flags field equal to
V4L2_SEL_TOP_FIXED | V4L2_SEL_LEFT_FIXED |
V4L2_SEL_WIDTH_GE | V4L2_SEL_HEIGHT_GE.
- VIDIOC_COMPOSE with flags field equal to
V4L2_SEL_TOP_FIXED | V4L2_SEL_LEFT_FIXED |
V4L2_SEL_WIDTH_LE | V4L2_SEL_HEIGHT_LE
Feel free to add a new flag if necessary.
4. Possible improvements and extensions.
- combine composing and cropping ioctl into a single ioctl
- add subpixel resolution
* hardware is often capable of subpixel processing. The ioctl triple
S_EXTCROP, S_SCALE, S_COMPOSE can be converted to S_EXTCROP and
S_COMPOSE
pair if a subpixel resolution is supported
What it your opinion about proposed solutions?
Looking for a reply,
Best regards,
Tomasz Stanislawski
Tomasz Stanislawski (2):
v4l: add support for extended crop/compose API
v4l: simulate old crop API using extcrop/compose
drivers/media/video/v4l2-compat-ioctl32.c | 4 +
drivers/media/video/v4l2-ioctl.c | 102
+++++++++++++++++++++++++++--
include/linux/videodev2.h | 30 +++++++++
include/media/v4l2-ioctl.h | 8 ++
4 files changed, 137 insertions(+), 7 deletions(-)
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